17th Edition Training Manual

th 17

Edition

Training Manual  Up to date to Amendment 3  Fully illustrated  Prepare for 2382-15

* not endorsed by City & Guilds

17th Edition Training Manual Copyright © 2015 Electacourse, a Clayton Partners Service All rights reserved. No part of this ebook may be reprinted or reproduced or utilised in any form by any electronic, mechanical, or other means now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers. The single exception to this is the right for the purchaser of this ebook to print pages for their personal study. The reproduction of copies of the material from this ebook in a classroom or training environment is expressly prohibited. Any contravention of these rights is liable to criminal prosecution for piracy under the terms of the Digital Economy Act 2010. ebook published by Electacourse in the United Kingdom The White House, Hunston, Chichester, PO19 1UP www.electacourse.com First publication January 2015 Electacourse catalogue reference: elc100-3 ISBN 13: 978-1-910404-05-8 (ebook-PDF) Also available : 17th Edition 2382-15 Exam Simulator for PC and MAC computers The publisher and author disclaim any liability, in whole or in part, arising from information contained in this publication. The reader is urged to consult with an appropriate licensed professional prior to taking any action or making any interpretation that is within the realm of a licensed professional practice. Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Site licenses and multiple copy purchases for FE colleges and training providers: [email protected]

17th Edition Training Manual

CONTENTS CONTENTS ............................................................................................................................................................................................................... 2 MODULE 1: BS7671 – REQUIREMENTS FOR ELECTRICAL INSTALLATIONS ....................................................................................................... 8 Why is the 17th Edition important to electricians? ...................................................................................................................................... 8 About this eBook course .................................................................................................................................................................................. 8 What you will learn in this course .................................................................................................................................................................. 9 How this course is organised ........................................................................................................................................................................ 10 ABOUT THE 17TH EDITION ................................................................................................................................................................................... 11 Introduction to the 17th Edition ..................................................................................................................................................................... 11 17th Edition History ......................................................................................................................................................................................... 13 LAYOUT OF THE REGULATIONS ............................................................................................................................................................................ 18 17th Edition Wiring Regulations - Structure ............................................................................................................................................... 18 ABOUT THE 2382-15 EXAM................................................................................................................................................................................... 21 How is the Exam Structured ......................................................................................................................................................................... 22 NUMBERING OF THE 17TH EDITION WIRING REGULATIONS ............................................................................................................................. 25 Numbering ....................................................................................................................................................................................................... 25 MODULE 2: PART 1 - SCOPE, OBJECTIVE & FUNDAMENTAL PRINCIPLES ....................................................................................................... 28 Ch 11 - Scope of the Regulations ................................................................................................................................................................... 29 Ch12 - Objects and effects .............................................................................................................................................................................. 31 Ch13 - Fundamental Principles ..................................................................................................................................................................... 31 REVIEW QUESTIONS – Scope, Object and Fundamental Principles ..................................................................................................... 34 ANSWERS – Scope, Object and Fundamental Principles ......................................................................................................................... 36

© 2008-2015 Electacourse

Page | 2

17th Edition Training Manual MODULE 3:PART 2 - DEFINITIONS – NEW AND CHANGED .............................................................................................................................. 37 New definitions and changed definitions ................................................................................................................................................... 37 Definitions ........................................................................................................................................................................................................ 38 Significant regulations new to 17th Edition.................................................................................................................................................. 43 Section summary ............................................................................................................................................................................................. 44 PART 2 - DEFINITIONS - TYPES OF SYSTEM & EARTHING ARRANGEMENTS AND VOLTAGE TERMS ................................................................ 45 Section Objectives ........................................................................................................................................................................................... 45 Earthing Systems ............................................................................................................................................................................................. 45 Definitions Relating to Voltage Terms ......................................................................................................................................................... 47 Voltage bands relating to nominal voltage categories ............................................................................................................................... 47 PART 2 - DEFINITIONS - EXTERNAL INFLUENCE AND INTERNATIONAL PROTECTION CODE (IP CODE) ........................................................ 48 Section Objectives ........................................................................................................................................................................................... 48 External Influence ........................................................................................................................................................................................... 48 International Protection Code ....................................................................................................................................................................... 50 Definitions Summary ..................................................................................................................................................................................... 54 REVIEW QUESTIONS – Definitions ............................................................................................................................................................ 55 ANSWERS – Definitions ................................................................................................................................................................................ 57 MODULE 4 - PART 3 — ASSESSMENT OF GENERAL CHARACTERISTICS .......................................................................................................... 58 Section Overview ............................................................................................................................................................................................ 58 Ch31 -Purpose, Supplies & Structure ........................................................................................................................................................... 59 Ch32 - Classification of External Influences ................................................................................................................................................ 60 Ch33 - Compatibility of Characteristics ....................................................................................................................................................... 61 Ch 35 - Safety Services .................................................................................................................................................................................... 61 Ch 36 - Continuity of Service ......................................................................................................................................................................... 62 REVIEW QUESTIONS – Assessment of General Characteristics ............................................................................................................ 63


Page | 3

17th Edition Training Manual ANSWERS – Assessment of General Characteristics................................................................................................................................. 65 MODULE 5 - PART 4 — PROTECTION FOR SAFETY............................................................................................................................................ 66 Overview .......................................................................................................................................................................................................... 66 Ch41 - Protection Against Electric Shock .................................................................................................................................................... 66 Chapter 41 - Protection against electric shock ............................................................................................................................................ 74 BS 7671 Appendix 2 section 14 ...................................................................................................................................................................... 75 Ch42 - Protection Against Thermal Effects ................................................................................................................................................. 81 Protection against overheating...................................................................................................................................................................... 85 Ch43 - Protection Against Overcurrent ....................................................................................................................................................... 86 Ch44 - Protection Against Voltage Disturbances & Electromagnetic Disturbances .............................................................................. 93 REVIEW QUESTIONS – Part 4 Protection for Safety ................................................................................................................................ 97 ANSWERS – Protection for safety ................................................................................................................................................................ 99 PART 5 — SELECTION & ERECTION OF EQUIPMENT ......................................................................................................................................... 100 Ch 51 - Common Rules ................................................................................................................................................................................. 101 Ch52 - Selection & Erection of Wiring Systems ........................................................................................................................................ 104 Ch53 - Protection, Isolation, Switching Control and Monitoring .......................................................................................................... 115 Table 53.4 – Guidance on the selection of protective, isolation and switching devices ...................................................................... 117 Ch54 - Earthing Arrangements & Protective Conductors ....................................................................................................................... 122 Earthing arrangements explained .............................................................................................................................................................. 123 Ch55 - Other Equipment .............................................................................................................................................................................. 142 New Section 557 - Auxiliary Circuits ......................................................................................................................................................... 146 Ch56 - Safety services ................................................................................................................................................................................... 152 REVIEW QUESTIONS – Selection and erection of equipment .............................................................................................................. 156 ANSWERS – Selection and erection of equipment .................................................................................................................................. 158 PART 6 — INSPECTION & TESTING .................................................................................................................................................................... 159


Page | 4

17th Edition Training Manual Overview ........................................................................................................................................................................................................ 159 Ch 61 - Initial Verification ............................................................................................................................................................................ 160 Ch62 - Periodic Inspection & Testing ......................................................................................................................................................... 164 Ch 63 - Certification & Reporting ............................................................................................................................................................... 165 REVIEW QUESTIONS – Inspection and Testing ..................................................................................................................................... 168 ANSWERS – Inspection and Testing.......................................................................................................................................................... 170 MODULE 5 - PART 7 — SPECIAL INSTALLATIONS OR LOCATIONS ................................................................................................................ 171 Overview ........................................................................................................................................................................................................ 171 Section 701 - Locations containing a bath or shower ............................................................................................................................... 172 Section 702 - Swimming Pools & Other Basins ......................................................................................................................................... 178 Section 703 - Rooms & Cabins Containing Sauna Heaters ...................................................................................................................... 182 Section 704 - Construction and Demolition Sites...................................................................................................................................... 184 Section 705 - Agricultural & Horticultural Premises ............................................................................................................................... 187 Section 706 - Conducting Locations with Restricted Movement............................................................................................................ 191 Section 708 - Electrical Installations in Caravan/Camping Parks and Similar Locations ................................................................... 192 Section 709 - Marinas and Similar Locations ............................................................................................................................................ 194 Section 710 - Medical Locations .................................................................................................................................................................. 198 Section 711 - Exhibitions, Shows and Stands ............................................................................................................................................ 203 Section 712 - Solar Photovoltaic (PV) Power Supply Systems ................................................................................................................ 205 Section 714 – Outdoor lighting installations ............................................................................................................................................. 207 Section 715 Extra-low voltage lighting installations ................................................................................................................................ 208 Section 717 - Mobile or Transportable Units ............................................................................................................................................. 210 Section 721 - Electrical Installations in Caravans and Motor Caravans ................................................................................................ 212 Section 722 – Electric Vehicle Charging ..................................................................................................................................................... 216 Section 729 - Operating and Maintenance Gangways ............................................................................................................................. 217


Page | 5

17th Edition Training Manual Section 740 - Temporary Electrical Installations for Structures, Amusement Devices and Booths at Fairgrounds, Amusement Parks and Circuses ........................................................................................................................................................................................ 219 Section 753 - Floor and Ceiling Heating Systems ..................................................................................................................................... 222 REVIEW QUESTIONS – Special Installations or Locations .................................................................................................................... 224 ANSWERS – Special Installations or Locations ........................................................................................................................................ 226 PART 8 – APPENDICES ........................................................................................................................................................................................ 227 AppendicesOverview ................................................................................................................................................................................... 227 Appendix 1:British Standards Referenced by the Regulations............................................................................................................... 228 Appendix 2: Statutory Regulations and Associated Memoranda .......................................................................................................... 228 Appendix 3:Time / Current Characteristics of Overcurrent Protective Devices and Residual Current Devices ............................ 228 Appendix 4: Current-Carrying Capacity and Voltage Drop for Cables and Flexible Cords ............................................................. 228 Appendix 5: Classification of External Influences.................................................................................................................................... 228 Appendix 6:Model Forms for Certification and Reporting..................................................................................................................... 229 Appendix 7:Harmonized Cable Core Colours .......................................................................................................................................... 229 Appendix 8: Current-Carrying Capacity and Voltage-Drop for Busbar Trunking and Powertrack Systems................................. 229 Appendix 9:Definitions — Multiple Source, D.C. and Other Systems.................................................................................................. 230 Appendix 10: Protection of Conductors in Parallel Against Overcurrent ............................................................................................ 230 Appendix 11:Effect of Harmonic Currents on Balanced Three-Phase Systems ................................................................................... 230 Appendix 12: Volts Drop in Consumers Installations ............................................................................................................................. 230 Appendix 13:Methods for Measuring the Insulation Resistance/Impedance of Floors & Walls to Earth or to the Protective Conductor System ......................................................................................................................................................................................... 230 Appendix 14:Measurement of Earth Fault Loop Impedance: Consideration of the Increase of the Resistance of Conductors with Increase of Temperature .............................................................................................................................................................................. 231 Appendix 16: Devices for protection against overvoltage ...................................................................................................................... 231 REVIEW QUESTIONS – Appendices......................................................................................................................................................... 232


Page | 6

17th Edition Training Manual ANSWERS – Appendices ............................................................................................................................................................................. 234 CITY & GUILDS 2382-15 SAMPLE EXAM QUESTIONS ......................................................................................................................................... 235 REVIEW QUESTIONS – City & Guilds 2382-15 ....................................................................................................................................... 236 ANSWERS – City & Guilds 2382-15 ........................................................................................................................................................... 248 2382-15 EXAM SIMULATOR ................................................................................................................................................................................ 250 LIST OF ILLUSTRATIONS ...................................................................................................................................................................................... 255 LIST OF TABLES.................................................................................................................................................................................................... 258 WHAT NEXT? ....................................................................................................................................................................................................... 259


Page | 7


MODULE 1: BS7671 – REQUIREMENTS FOR ELECTRICAL INSTALLATIONS

Known as 17th Edition, the IET Wiring Regulations are the British Standards relating to requirements for electrical installations in the UK.

Why is the 17th Edition important to electricians? The 17th Edition is of critical importance to electricians and to all who work in the electrical industry. All new electrical installations need to conform to the requirements of the British Standard 7671:2008 as detailed in the 17th Edition including Amendments 1, 2 and 3, of the requirements. The 17th Edition is the essential source of reference for low voltage electrical installations in the UK. It is the foundation of knowledge for electrical contractors and installers.


About this eBook course The aim of this course is to prepare candidates for the City & Guilds 2382-15 examination. An electrician passing the 238215 is known as 17th Edition Qualified and is able to demonstrate a good understanding of the British Standards relating to wiring and electrical installations. All electricians practising in the UK need to know and need to be able to reference the wiring regulations in order to undertake their work to a professional standard.

Page | 8

17th Edition Training Manual The 17th Edition Wiring Regulations is not a statutory document. However in the event of a dispute, individuals responsible for faulty installations who are unable to demonstrate understanding of the Regulations, are at risk of assuming legal liability.

2382-15 Examination

City & Guilds

An open book examination is an assessment which allows candidates to have reference material with them in the exam itself. The exam questions are written on the assumption the candidate has the book alongside them as they answer the questions. For the 2382-15, the reference material is a copy of the 17th Edition Wiring Regulations. You are also allowed to take in a calculator.

City & Guilds are the accrediting institution for assessing individuals’ understanding of the 17th Edition Wiring Regulations.

The 2382-15 examination is a so-called open book examination; it takes take place at accredited City & Guilds examination centres. There is no requirement for any practical work.

You are not allowed to mark up the 17th Edition Wiring Regulations with notes.

What you will learn in this course After you have studied this course you will 1. be familiar with all aspects of the 17th Wiring Regulations 2. know how and where to quickly locate critical information in the 17th Wiring Regulations 3. understand the structure of the 2382-15 exam 4. have had the opportunity to practice exam questions Achievement of the 2382-15 qualification ensures individuals are up-to-date with the latest industry regulations on wiring and the safe use and operation of electrical equipment and systems.


You may already have purchased the Electacourse 2382-15 Exam Simulator alongside this course, however if you chose to buy this course alone, you can still buy the simulator separately from electacourse.com.

Page | 9

17th Edition Training Manual Many thousands of candidates have used this and the previous versions of the Electacourse 17th Edition course to prepare themselves for the City & Guilds 2382-15 exam. Feedback indicates that Electacourse candidates tend to pass the 2382-15 exam with higher marks than those who have studied at training centres.

How this course is organised Like many courses and eBooks, the 17th Edition Wiring Regulations course is organised both as a linear course and as a reference where you can dip in and out of modules, chapters or sections. It is not a requirement that you have to complete one module before moving on to the next. If you feel confident about one chapter, then you have the choice to skip it and move on to another. We recommend however, that you do review all chapters. The course is organised into 5 Modules, each module contains a number of chapters or parts. The first module introduces the background to the 17th Edition, the nature of the exam and how the Regulations are organised. The other four modules align closely to the parts which make up the general structure of the 17th Edition Wiring Regulations. Within each part, there are chapters, some of which are split into sections. Each chapter covers a discrete, bite size set of the Regulations. We recommend you study one chapter at a time and once you have completed a chapter, take a break. If you wish you can study more than one chapter a day. Some of the chapters, particularly in Module 1 are quite short. But if you do take more than one chapter at a time,


avoid extending yourself. Too much time spent studying can lead to lack of a concentration and prevents good learning of the information contained in each chapter. Most modules conclude with a small quiz to test your understanding of the material which was covered in the section. At the end of the course is a longer quiz which tests your understanding of the complete 17th Edition Regulations

The Modules are

Module 1 – Introduction Introduces the aims of the course and what you may expect to achieve from studying the course Module 2 – Part 1 – Scope, Objective and Fundamental Principles This short module introduces the scope and aims of the Regulations. Module 3 – Definitions The Regulations contain hundreds of definitions. Knowledge of the definitions assists understanding of the Regulations Module 4 – Parts 3, 4, 5 and 6 These Parts contain the body of the Regulations. It is essential to be able to go quickly to any chapter or section within these Parts. Module 5 – Part 7 and Appendices Part 7 covers special installations or locations

Page | 10


ABOUT THE 17TH EDITION

Introduction to the 17th Edition The 17th Edition Wiring Regulations is a big book: it is over 450 pages long and covers thousands of regulations. Some courses try to teach this material using videos, animations and other multi-media methods. Although such media can help students understand the principles of the wiring regulations, on their own they are not sufficient to get under the skin of the Regulations. There is more information to be understood and learnt than can be taught in a series of slide presentations or video clips. Also, as the exam is open book and is designed to test your understanding of how to find out information about the regulations which cover your day


to day work, no amount of entertaining voice-overs or animations is going to help you get to know your way round the densely packed 17th Edition Wiring Regulations. This course is designed to draw your attention to the critical areas of the Regulations, to indicate what has changed in the 17th Edition and to prepare you for the exam. You will complete the course secure in the knowledge you know how to locate and apply relevant regulations in your daily work. This secure knowledge will give you the best chance of achieving a good pass at the 2382-15 examination. Unlike courses which are undertaken over a few intense days at a training centre, this course gives you the

Page | 11

17th Edition Training Manual opportunity to study at your own pace and in your time to give you the best opportunity of understanding the Regulations and to passing the 2382-15 exam. If you do not already have a copy of the 17th Edition Wiring Regulations Yellow Book, then you need to buy one now. Click here or on the Yellow Book to go to Amazon.co.uk.

Fig. 1 The IET, publisher of the Wiring Regulations

Fig. 2 17th Edition Wiring Regulations, you can purchase the book new or second hand from Amazon. If you buy it second hand, make sure it does not have any pencil or pen markings inside.


Page | 12

17th Edition Training Manual 17th Edition History

Fig. 3 The first electric street lamps in the UK

In 1881 the first public electricity supply in the world was turned on in Godalming in Surrey, where gas street lights were replaced by electrical street lamps based on a system supplied by the German company Siemens. No sooner had the system been activated than the technical press reported issues associated with wiring. The lighting in side streets was dim and of poor quality due to the inadequacy of the cabling. There were also reports of children (and drunks) harming themselves on the exposed wires.


Page | 13

17th Edition Training Manual In the next year, the first edition of the British Wiring regulations was published. It was published by the Society of Telegraph Engineers and of Electricians and contained just four pages under the title Rules and Regulations for the Prevention of Fire Risks Arising from Electric Lighting. The purpose of the Regulations were to ensure that workmanship was of the highest order and that the materials used are of suitable quality to do the work required and that the installations were safe. We think the first regulations are so interesting, we have reproduced them in full at the end of this module. Courtesy of the IET. The wiring regulations remained the responsibility of what became the Institute of Electrical Engineers (and later


became IET) and in 1981 became aligned to IEC (International Electrotechnical Commission) standards. Eleven years later, the regulations became a British Standards document and the harmonisation of wiring regulations became formalised. Further international harmonisation of standards aligns wiring regulations to CENELEC (European Committee for Electrotechnical Standardization) The most recent edition of the wiring regulations is the 17th Edition which was published in June 2008 as BS7671:2008. In July 2011, Amendment 1 to the regulations was published under a green cover and came into force in January 2012. In 2013 a Corrigendum and Amendment 2 covering electric vehicles were published.

Page | 14

17th Edition Training Manual A major amendment, Amendment 3 was published in January 2105. This amendment included many changes

which are applicable from 1st July 2105. This course is up to date to Amendment 3.

Time line of the publication of the 17th Edition of the Wiring Regulations


Page | 15



Page | 16



Page | 17


LAYOUT OF THE REGULATIONS

The 17th Edition Wiring Regulations are organised in to a structure containing 7 Parts and the Appendices

17th Edition Wiring Regulations - Structure



Key fact

Each part contains a chapter, each chapter contains sections, each section contains regulations. The Regulations themselves may contain multiple clauses. The Regulations is a well organised but complex document. The 17th Edition Wiring Regulations contains seven parts


and sixteen appendices. Within this structure there are many thousands of regulations which although you are not expected to know by heart, you are expected to know where to find relevant regulations. The core of the regulations is Part 3 to Part 7. Around these core specialist parts is the introductory Part 1, the Definitions which apply to all parts, Part 2, and the 16 Appendices which contain detailed regulatory information, tables and measurements. The Regulations themselves are contained with Sections and Chapters of the Parts of the 17th Edition

Page | 18

17th Edition Training Manual The 16 Appendices Of The 17th Edition Wiring Regulations • • • • • • • • • Fig. 4 Basic structure of the Regulations

The 7 Parts Of The 17th Edition Wiring Regulations Part 1

Scope, object and fundamental principles

Part 2

Definitions

Part 3

Assessment of general characteristics

Part 4

Protection for safety

Part 5

Selection and erection of equipment

Part 6

Inspection and testing

Part 7

Special installations or locations

• • • •

•

• •


British Standards to which reference is made in the Regulations Statutory regulations and associated memoranda Time/current characteristics of overcurrent protective devices and RCDs" Current-carrying capacity and voltage drop for cables Classification of external influences Model forms for certification and reporting Harmonized cable core colours Current-carrying capacity and voltage drop for busbar trunking and powertrack systems Definitions – multiple source, d.c. and other systems Protection of conductors in parallel against overcurrent Effect of harmonic currents on ... Moved to Appendix 4 sec 5.5 and 5.6 Voltage drop in consumers’ installations…Moved Appendix 4 sec 6.4 Methods for measuring the insulation resistance/impedance of floors and walls to Earth or to the protective conductor system Measurement of earth fault loop impedance: consideration of the increase of the resistance of conductors with increase of temperature Ring and radial final circuit arrangements, Regulation 433.1 Devices for protection against overvoltage

Page | 19

17th Edition Training Manual *Note that following the update BS7671:2008 Amendment 1 in 2011, two of the appendices, 11 and 12, have been moved to Appendix 4. In effect this means there are in fact only fourteen appendices which contain information. Appendices 11 and 12 remain in the 17th Edition Wiring Regulations for information purposes.

Fig. 5 Structure of the 17th Edition Wiring Regulations

Understanding the Structure of the Regulations

Although there are 7 parts and 16 Appendices, the 17th Edition Wiring Regulations can best be understood by considering it as organised into four chunks of information: 1. Part 1- Scope, object and fundamental principles This section outlines general requirements for installations 2. Part 2 – Definitions This section details the 290 definitions which are used in the Regulations 3. Part 3 to Part 7 This is the body of the regulations, each part deals with a critical area of wiring regulations. Parts 3 to 6 describe general regulations in details and the longest part, Part 7 deals with special installations and locations. 4. Appendices The extensive appendices provide detail information related to the Wiring Regulations


Page | 20


ABOUT THE 2382-15 EXAM

Fig. 6The 2382-15 exam is set and administered by City & Guilds.

The 2382-15 is available at exam centres around the UK. City & Guilds assess a requirement that candidates undertake at least 35 study hours prior to sitting the exam. The 2382-15 exam is an ‘open book’ exam. That means candidates can take into the exam room a copy of the 17th Edition Wiring Regulations (the Yellow Book). You can also take in a calculator. You are not allowed to mark up the Green Book with written notes; it needs to be a ‘clean’ copy.


At the examination centre candidates sit the exam at a computer which is connected online with the City & Guilds. In most cases the exam centre will be able to give candidates information about how well they have performed in the exam within 30 minutes of completing the exam. All the exam questions are of the multiple choice type; that is, one



Top tip

Become familiar with the index of the Regulations. In your exam the quickest way to find your way around the Yellow Book is to start with the index. The index is your friend.

Page | 21

17th Edition Training Manual question statement with four possible answers of which one is correct. When studying this course and preparing for the 2382 exam it is important that candidates understand that the exam is not only testing your understanding of the 17th Edition Wiring Regulations, it is testing your knowledge of the

Green Book and your ability to locate in the book answers to the exam questions. So, do not try to remember everything in this course, but do remember how to use this information to find the relevant sections from the 17th Edition Wiring Regulations.

How is the Exam Structured The following gives detailed weighting information for the 17th Edition 2382-15 exam at the time of publication. You do not need to learn the weighting, but it serves as a very good indication as to what information you will need to retrieve from the 17th Edition Wiring Regulations in order to pass your exam.

Fig. 7 The number and percentage of questions for each section of the 2382-15 exam


Page | 22

17th Edition Training Manual Part 1 - Understanding Scope, Object and Fundamental Principles Weighting - 6% Number of questions – 4

For this part of the exam you need to refer to all Parts of the Regulations, but of particular importance are: 1) Identify examples of installations in the Scope of BS 7671:2008 and particular requirement for specific installations and locations. 2) Identify the object of BS 7671: 2008. 3) Identify the fundamental principles of BS7671

Part 2 – Definitions

Weighting - 4% Number of questions – 2 Refer to Part 2 of the 17th Edition Wiring Regulations 1) Interpret the definitions used within BS7671 2) Relate the definitions to the regulations and appendices of BS7671 Although this Part has a small weighting towards the 238215 exam and only two questions, a clear understanding of the Definitions Part of the Regulations will help considerably when working through questions relating to the other Parts of the regulations. You will find that becoming familiar with the ‘System’ definition will specifically help you when sitting the 2382-15 exam.


Part 3 – Understand how to assess the general characteristics of electrical installations Weighting - 10% Number of questions – 6

Please refer to the relevant parts of the regulations and:

1) Interpret the requirements of assessing the general characteristics of electrical installations within the scope of BS7671 2) You should be able to state the need to consider compatibility and maintainability in the selection of equipment and the need to divide an installation into suitable circuit arrangements. 3) Determine the number and types of Live conductors for installation circuits and state the source (e.g. standby, external) and characteristics necessary for a supply.

Part 4 – Understand the requirements for protection for safety for electrical installations Weighting - 25% Number of questions – 15


1) Identify the requirements of protection for safety within the scope of BS7671 2) Identify how this applies to the electrical installations within the scope of BS7671, including: 3) Protection against electric shock 4) Protection against thermal effects 5) Protection against overcurrent 6) Protection against electromagnetic and voltage disturbances 7) Describe how the requirements for shock protection are

Page | 23

17th Edition Training Manual affected by: a) Value of external earth loop Impedance (Ze) b) Compliance with Zs=R1 + R2 + Ze c) Compliance with tables 41.2-6 8) Describe means of protection against fire, burns and harmful thermal effects. 9) Identify the difference between overcurrent and fault current 10) Describe methods of overcurrent and fault current protection and the need for coordination with conductors and equipment. 11) State the requirements for protection against a) Overvoltage b) Undervoltage 12) Identify precautions where particular risk of danger of fire exists.

Part 5 – Understand the requirements for selection and erection of equipment for electrical installations Weighting — 23% Number of questions — 14


1) Identify the requirements for selecting and erecting equipment within the scope of BS7671 2) Interpret how this applies to electrical installations, including: 3) Common rules 4) Selection and erection of wiring systems 5) Protection, isolation, switching, control and


6) 7) 8) 9)

Monitoring Earthing arrangements and protective conductors Other equipment including Auxiliary circuits Safety services

Part 6 – Understand the requirements for inspection and testing of electrical installations Weighting — 7% Number of questions — 4


1) Identify the requirements for inspection and testing of electrical installations. 2) Interpret how this applies to electrical installations.

Part 7 – Understand the requirements of special installations or locations as identified in BS7671 Weighting — 17% Number of questions — 10

Please refer to the relevant parts of the regulations and: 1) Identify the requirements for special installations and locations. 2) Interpret how these affect the general requirements of the regulations.

Appendix – Understand the information contained within the appendices of BS7671 Weighting — 8% Number of questions — 5

1) Identify the information in the appendices of BS7671. 2) Specify how the information contained in the appendices is used to support electrical installation activities.

Page | 24


NUMBERING OF THE 17TH EDITION WIRING REGULATIONS

The aim of this section is to give you an understanding of the numbering system which is used in the 17th Edition Wiring Regulations. Understanding of the numbering system enables you to quickly locate the relevant regulations and gives guidance on how to work your way through the exam and the 17th Edition Wiring Regulations

Numbering The numbering of the 17th Edition Wiring Regulations follows the pattern of the technical intent of Standards developed at the European CENELEC level. The system is based on the harmonisation documents HD60364 series of standards. Or, in language the rest of us understand, the numbering system has designed to be consistent, easy to follow and easy to update. For the old timers amongst us who wired our first socket under the 16th Edition Regulations, the most obvious change is that the 17th Edition Wiring Regulations has dropped the dashes and now uses a point/dot numbering system, based on the IEC numbering system.


Page | 25

17th Edition Training Manual The structure of the numbering is straightforward:

Regulation 524.1 Refers to:

1st digit still signifies a Part (Part 5 of BS 7671 in the

PART 5 - SELECTION AND ERECTION OF EQUIPMENT

example below),

CHAPTER 2 - SELECTION AND ERECTION OF WIRING SYSTEMS

2nd digit is a Chapter (the second chapter of Part 5), 3rd digit is a Section (the fourth section of 52) The subsequent number/s are the Regulation (or group of Regulation) number/s (1 of 524)

SECTION 4 - CROSS-SECTIONAL AREAS OF CONDUCTORS REGULATION 1

Using the example of Regulation 524.1

The cross-sectional area of each conductor in a circuit shall be not less than the values given in Table 52.3, except as provided for extra-low voltage lighting installations according to Regulation 559.11.5.2.

Some regulations are organized into Regulation Groups, by example:Regulation 521.9.3 refers to:

REGULATION- GROUP 9Use of flexible cables

PART 5 - SELECTION AND ERECTION OF EQUIPMENT

Stationary equipment which is moved temporarily for the purposes of connecting, cleaning etc., e.g. cookers or flush mounting units for installations in false floors, shall be connected with flexible cable. If the equipment is not subject to vibration then non-flexible cables may be used.

CHAPTER 2 - SELECTION AND ERECTION OF WIRING SYSTEMS SECTION 1 - TYPES OF WIRING SYSTEM


REGULATION 3

Page | 26

17th Edition Training Manual UK Only Numbering

The 17th edition introduced a new IEC decimal point numbering system to make it easier to embody future changes and additions resulting from ongoing international standards work within IEC and CENELEC. In order to accommodate future IEC changes it was decided to have a 100 numbering system for UK only regulations. For the third amendment, the 100 numbers now represent CENELEC Harmonization Document reference numbers and 200 numbers represent UK-only regulations. Existing regulations have not been "updated" to indicate 100 and 200 numbers; that will only be done when those regulations require a significant rewrite.

Fig. 8 Page of the Regulations showing ‘dot’ numbering


Page | 27


MODULE 2: PART 1 - SCOPE, OBJECTIVE & FUNDAMENTAL PRINCIPLES

The aim of this chapter is to give an understanding of Part 1 of the Regulations, you will learn which are the critical elements of Part 1 Part 1 serves as an introduction to the regulations and outlines very general guidelines for the requirements for installations. This first Part is not as exacting as the rest of the regulations, but it lays a very good foundation for the way that all installers and designers should think.

The chapters included in Part 1 are Ch 11

Scope - Range and exclusions of installation

Ch 12

Objects and effects - Materials, precautions

and effects standards Ch 13

Fundamental principles - Workmanship,

overcurrent, earth leakage, isolation and switching, inspection and testing


Page | 28

17th Edition Training Manual Ch 11 - Scope of the Regulations Within the scope of the Regulations The Scope of the regulations apply to the design, erection and verification of electrical installations, such as those of: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

Residential premises Commercial premises Public premises Industrial premises Agricultural and horticultural premises Prefabricated buildings Caravans, caravan parks, and similar sites Construction sites, exhibitions, shows, fairgrounds and other Installations for temporary purposes Marinas External lighting and similar installations Mobile or transportable units Photovoltaic systems Low Voltage generating sets Highway equipment and street furniture Medical locations Operating and maintenance gangways


110.1.2 Additional requirements are included in the regulations for: 1. Circuits supplied at nominal voltages up to and including 1000 VAC or 1500 VDC; for AC, the preferred frequencies, which are taken into account in this Standard are 50 Hz, 60 Hz and 400 Hz. The use of other frequencies for special purposes is not excluded: 2. Circuits, other than the internal wiring of apparatus, operating at voltages exceeding 1000V and derived from an installation having a voltage not exceeding 1000 VAC. e.g. Discharge lighting. 3. Wiring systems and cables not specifically covered by the standards for appliances 4. All consumer installations external to buildings 5. Fixed wiring for information and communication technology, signalling, control and the like 6. Additions and alterations to installations and parts of the existing installation affected by an addition or alteration.

Page | 29

17th Edition Training Manual Outside the scope of the Regulations

Installations that are excluded from BS 7671: 2008: 1. Distributor ’s equipment as defined in the Electricity Safety, Quality and Continuity Regulations 2002 2. Railway traction equipment, rolling stock and signalling equipment 3. Equipment of motor vehicles, except those to which the requirements of the Regulations concerning caravans or mobile units are applicable 4. Equipment on board ships 5. Equipment of mobile and fixed offshore installations 6. Equipment of aircraft 7. Those aspects of mines and quarries specifically covered by Statutory Regulations 8. Radio interference suppression equipment, except so far as it affects safety of the electrical installation 9. Lightning protection of buildings covered by BS 6651 10. Those aspects of lift installations covered by BS 5655 and BS EN 81-1 11. Electrical equipment of machines 12. Electric fences

Fig. 9 Outside scope of Regulations


Page | 30

17th Edition Training Manual Statutory Control & Installation Requirements

electrician to know and every part, while not specific, should be fully understood; it is the foundation for all other requirements. However, when sitting the 2382-15, do not rely on referencing Chapter 13, in nearly all cases, the questions you will be asked will require you to refer to the regulations in the detailed Parts and Chapters.

Part 1, Chapter 11, Section 115 states that for installations in premises over which a licensing or other authority exercises a statutory control, the requirements of that authority shall be ascertained and complied with in the design and execution of the installation.

Chapter 13 and BS7671 in general, exists to provide for the safety of persons, livestock and property against dangers and damage which may arise in the reasonable use of electrical installations.

Ch12 - Objects and effects

Risk of injury can arise from:

In general, the Regulations are non-statutory; however, they can be used as evidence to claim compliance with a statutory requirement. The statutory requirements that the BS 7671 support are listed in Appendix 2 of the Regulations, according to their application.

This is a short chapter which is unlikely to prompt any questions in 2382-15. This chapter introduces the structure of the rest of the Regulations. It does contain the important note that if the designer deviates from any part of the Regulations, the resulting degree of safety is not less than that obtained by compliance with the Regulations.

Ch13 - Fundamental Principles Although the regulations relating to Protection for Safety are detailed in Part 4, this chapter, Chapter 13 states the fundamental principles relating to protection for safety, design, selection, erection and verification of electrical installations. All the principles covered in this chapter will be repeated at relevant sections later on. This duplication matches the duplication in the Regulations. Chapter 13 is a broad but very crucial chapter to for an


131.1 General - Risk of injury

1. Shock currents A person or livestock can be protected against shock by direct contact, by limiting the current which can pass through a body to a non-hazardous value. Fault protection can also protect against shock by limiting the magnitude of a current to a nonhazardous value, and by limiting the duration of the current to a non-hazardous time period. The method of equipotential bonding is an important principle for protection for safety. Note that the definition for ‘direct contact’ has been deleted by BS7671:2008 and is now covered by the ‘basic protection’ definition. 2. Excessive temperatures likely to cause burns and fires To protect against thermal effects, the installation must be arranged that the risk of ignition of flammable materials is minimized. The factors of

Page | 31


3. 4.

5. 6.

7.

combustion, ignition, or degradation of materials, risk of burns, and impairment of the safe function of installed equipment should be taken into consideration. Ignition of potentially explosive atmosphere Undervoltages, overvoltages and electromagnetic influences likely to cause or result in injury or damage Personnel and livestock should be protected against effects of a fault between live parts of circuits supplied at different voltages and atmospheric events. In addition, protection must be provided for undervoltage and the subsequent recovery. When installed, there should be an adequate level of immunity against electromagnetic disturbances by taking into consideration electromagnetic emissions that the installation will produce. Mechanical movement of electrically actuated equipment therefore causing injury Power supply interruptions of safety services When damage or danger is expected to arise due to an interruption of supply, suitable provisions shall be made in the installation or installed equipment. Arcing, likely to cause blinding effects, excessive pressure, and/or toxic gases

132 Installation Design

The installation should be designed for the protection of persons, livestock and property and for the proper functioning of the installation for intended use.


The following characteristics should be included in the documentation to show conformity with the Regulations. This section has been the source of exam questions. •

Nature of current (AC / DC)

•

Purpose and number of conductors:

•

For AC: Line conductors, neutral conductors, protective conductor, PEN conductors

•

For DC: Conductors equivalent to those listed above (outer/middle/earthed live conductors, protective conductor, PEN conductor)

•

Values and tolerances:

•

Nominal voltage and voltage tolerances

•

Nominal frequency and frequency tolerances

•

Maximum current allowable

•

Earth-fault loop impedance

•

Protective measures inherent in the supply (earthed neutral of mid-wire)

•

Particular requirements of the distributor.

•

The nature of the demand should be determined from knowledge of:

•

Location of points of power demand

•

Loads to be expected on the various circuits

•

Daily and yearly variation of the demand

•

Harmonics and any other special conditions

•

Anticipated future demand

•

Requirements for control, signalling,

Page | 32

17th Edition Training Manual communication and information technology •

If a supply for safety services is specified, the following should be determined:

•

Source of supply

•

Circuits to be supplied by the electrical source for

electrical installation. When the installation is complete, a qualified individual should inspect and verify the installation's completion. They should also make a recommendation for subsequent periodic inspection and testing.

safety services or the standby electrical source Equipment exposed to the environment should be protected to prevent dangerous conditions. The cross-sectional area of conductors, the type of wiring and method of installation, and protective equipment should all be factors in the design with respect to both normal current loads and fault current loads. If a possibility of danger exists that would require immediate interruption of the supply of power, an interrupting device should be installed. Accessibility should be a factor for installation and repair, as well as disconnecting devices. All documentation should be supplied with the electrical device upon installation. A single-pole fuse, switch or circuit breaker shall be inserted in the line conductor only. NEVER should a switch, fuse or circuit breaker be inserted in an earthed neutral conductor. When selecting electrical equipment, compliance with the appropriate British Standard is mandatory. In addition, the voltage, current, frequency and power should all comply with the circuit's needs and capacities. At all times, good workmanship by skilled persons and proper materials should be used in the erection of the


Page | 33

17th Edition Training Manual REVIEW QUESTIONS – Scope, Object and Fundamental Principles

Question 1

Question 3

BS7671 Wiring Regulations do NOT apply to the design, erection and verification of:

BS7671 Wiring Regulations apply to the design, erection and verification of:

A.

public premises

A.

Equipment of mobile and fixed offshore installations

B.

photovoltaic systems

B.

Marinas

C.

equipment on board ships covered by BS 8450

C.

D.

external lighting and similar installations

Railway traction equipment, rolling stock and signalling equipment

D.

Electric fences covered by BS EN 60335-2-76.

Question 2 BS7671 Wiring Regulations do NOT apply to the design, erection and verification of:

Question 4

A.

low voltage generating sets

BS7671 Wiring Regulations may need to be supplemented by the requirements or recommendations of other standards in cases where they are applied to:

B.

public premises

A.

operating and maintenance gangways.

C.

prefabricated buildings

B.

low voltage generating sets

D.

aircraft equipment

C.

mobile or transportable units

D.

electrical installations for open-cast mines and quarries


Page | 34

17th Edition Training Manual Question 5

Question 7

One of the important principles for safety in connection with fault protection is the application of the method of

An interrupting device for emergency control shall be installed

A.

protective insulation

A.

B.

protective equipotential bonding

in such a way that it can be rapidly and effectively operated

C.

protective connection

B.

D.

equipotential insulation

in such a way that it can be easily recognized and effectively and rapidly operated for immediate interruption of the supply

Question 6

C.

closer to the power supply

Which characteristic does not need to be included in the documentation referred to in Regulation 132.13 to show conformity with the Regulations:

D.

in such a way that it can be easily recognized

A.

Particular requirements of the distributor.

B.

Nature of current: a.c. and/or d.c.

When equipment is not covered by a known standard, the designer must confirm the same degree of safety as afforded by

C.

The cost of equipment

A.

European standards

D.

Purpose and number of conductors

B.

British standards

C.

CENELEC standards

D.

IEC standards


Question 8

Page | 35


Question 10

The IET Requirements for Electrical Installations BS7671 applies for

The fundamental principles of BS 7671 covering design, states that every electrical installation shall be provided with

A.

electrical equipment on aircraft

A.

emergency control devices

B.

traction equipment

B.

fuses in the neutral conductor

C.

construction sites

C.

an alternative source of supply

D.

fire alarms fed from a safety source

D.

appropriate documentation

ANSWERS – Scope, Object and Fundamental Principles 1C, Ref: BS7671: 110.1.1, 110.2 2D, Ref: BS7671: 110.1.1, 110.2 3B, Ref: BS7671: 110.1.1, 110.2 4D, Ref: BS7671: 110.1.3 5B, Ref: BS7671: 131.2.2 6C, Ref: BS7671: 132.2 7B, Ref: BS7671: 132.9 8B, Ref: BS7671: 110.1.3 9C, Ref: BS7671: 110.1.1 10D, Ref: BS7671: 132.13


Page | 36


MODULE 3:PART 2 - DEFINITIONS – NEW AND CHANGED

New definitions and changed definitions The aim of this chapter is to draw attention to the many new definitions which are described in the 17th Edition Wiring Regulations. Some existing definitions have new words and descriptions. There are over 300 definitions in the 17th Edition Wiring Regulations, Amendment 3 — there were 170 in the 16th Edition. Some new definitions came in to the Regulations at the time of the first publication of the 17th Edition, others have been introduced more recently with the publication of © 2008-2015 Electacourse

Amendments 2 and 3. As with the previous chapter, this chapter introduces concepts which will be repeated later in the relevant Parts. This duplication is intentional; we aim to illustrate how the Regulations are structured. Itemised below is a complete list of all the Definitions, those that have been introduced in Amendment 3 are highlighted. Extended descriptions of significant new and changed definitions are detailed later in this section.

Page | 37

17th Edition Training Manual Definitions (New or significantly changed in Amendment 3 marked in RED 8/20 Current impulse, {534}.

Building void, non-accessible.

Accessory.

Bunched.

Central power supply system (low power output).

Agricultural and horticultural premises.xx

Busbar trunking system

Circuit. Circuit-breaker.

Ambient temperature

Bypass equipotential bonding conductor, {444}.

Amusement device.

Cable channel.

Circuit protective conductor (cpc).

Appliance.

Cable cleat.

Class I equipment.

Arm’s reach.

Cable coupler.

Class II equipment.

Arrangements for livestock keeping.

Cable ducting.

Class III equipment.

Auxiliary circuit.

Cable ladder.

Cold tail.

Back-up protection.

Cable tray.

Barrier.

Cable trunking.

Basic insulation.

Cable tunnel.

Common equipotential bonding system, common bonding network (CBN), {444}.

Basic protection.

Caravan.

Basin of fountain.

Caravan park / camping park.

Conducting location with restricted movement.

Bonding conductor.

Caravan pitch.

Conduit.

Bonding network (BN), {444}.

Connector.

Bonding ring conductor (BRC), {444}.

Caravan pitch electrical supply equipment.

Booth

Cartridge fuse link.

Building void, accessible.

Central power supply system.


Circuit-breaker, linked.

Complementary floor heating.

Consumer unit (may also be known as a consumer control unit or electricity control unit).

Page | 38

17th Edition Training Manual Continuous operating voltage (Uc),{534}.

Earth electrode resistance.

Controlgear

Earth fault loop impedance.

Conventional impulse withstand voltage.

Earth leakage current

Current-carrying capacity of a conductor.

Earthing.

Earth fault current.

Earthed concentric wiring.

Electrical supply system for safety services. Electrically independent earth electrodes. Electrode boiler (or electrode water heater).

Current-using equipment.

Earthing conductor.

Electronic convertor (static convertor).

d.c. system

Electric shock.

Emergency stopping.

Danger.

Electric vehicle (EV), {722}.

Emergency switching.

Electric vehicle charging point.

Enclosure.

Mode 1 charging.

Equipotential bonding.

Direct heating system.

Mode 2 charging.

Escape route.

Disconnector.

Mode 3 charging.

Exhibition.

Discrimination.

Mode 4 charging.

Exposed-conductive-part.

Distribution board.

Vehicle connector.

External influence.

Distribution circuit.

Vehicle coupler.

Extra-low voltage

Design current (of a circuit). Device for connecting a luminaire (DCL).

Equipment

Distributor.

Electrical circuit for safety services.

Extraneous-conductive-part.

Double insulation.

Electrical equipment (abbr: Equipment).

Fairground.

Earth.

Electrical installation (abbr: Installation).

Fault current.

Earth electrode.

Electrical source for safety services.

Duct, Ducting

Earth electrode network, {444}. © 2008-2015 Electacourse

Fault. Fault protection. Final circuit. Page | 39

17th Edition Training Manual Fixed equipment.

Highway.

Flexible cable.

Highway distribution board.

Low voltage switchgear and controlgear assembly.

Flexible sheet heating element.

Highway distribution circuit.

Luminaire.

Flexible wiring system.

Highway power supply.

Luminaire supporting coupler (LSC).

Follow-current interrupting rating, {534}.

Houseboat

Main earthing terminal.

Impulse current (Iimp), {534}.

Maintenance.

Functional bonding conductor, {444}.

Impulse withstand voltage, {534}.

Marina.

Functional earth.

Inspection.

Mechanical maintenance.

Functional extra-low voltage (FELV).

Installation.

Medical location, {710}.

Functional switching.

Instructed person (electrically).

Applied part.

Fuse.

Insulation.

Group 0.

Fuse carrier.

Insulation co-ordination, {534}.

Group 1.

Fuse element.

Isolation.

Group 2.

Fuse link.

Isolator.

Fused connection unit.

Ladder

Medical electrical equipment (ME equipment).

Gas installation pipe.

Leakage current.

Harmonized Standard.

Medical electrical system (ME system).

Leisure accommodation vehicle.

Hazardous-live-part.

Medical IT system.

Heating cable.

Lightning protection zone (LPZ), {534}.

Patient.

Heating-free area.

Line conductor.

Heating unit.

Live conductor.

Meshed bonding network (MESHBN), {444}.

High-density livestock rearing.

Live part.

Minimum illuminance.

High voltage

Low voltage

Minor works.


Patient environment.

Page | 40

17th Edition Training Manual Mobile and offshore installations.

PEM.

PV array junction box.

Mobile equipment

PEN conductor.

PV cell.

Mobile home.

Person

PV convertor.

Monitoring.

Phase conductor

PV d.c. main cable.

Motor caravan.

Pleasure craft.

PV generator.

Neutral conductor.

Plug.

PV generator junction box.

Nominal discharge current (Inspd), {534}.

Point (in wiring).

PV installation.

Portable equipment

PV module.

Nominal voltage

Powertrack.

PV string.

Non-flame propagating.

Powertrack system (PT system).

PV string cable.

Obstacle.

Prefabricated wiring system.

PV supply cable.

Open-circuit voltage under standard test conditions Uoc STC.

Prospective fault current (Ipf).

Rated current.

Operating and maintenance gangway, {729}.

Protective bonding conductor. Protective conductor (PE).

Rated impulse withstand voltage level (Uw), {534}.

Ordinary person.

Protective conductor current.

Reduced low voltage system.

Origin of an installation.

Protective earthing.

Reinforced insulation.

Origin of a temporary electrical installation.

Protective equipotential bonding.

Reporting.

Protective multiple earthing (PME).

Overcurrent.

Protective separation.

Residences and other locations belonging to agricultural and horticultural premises.

Overcurrent detection.

PV, {712}.

Residential park home.

Overload current.

PV a.c. module.

Residual current.

PEL.

PV array.

Residual current device (RCD).

PELV (protective extra-low voltage).

PV array cable.


Page | 41

17th Edition Training Manual Residual operating current.

Standby electrical source.

Resistance area (for an earth electrode only).

Standby electrical supply system.

Temporary overvoltage (UTOV), {534}.

Static convertor.

Temporary structure.

Response time.

Stationary equipment.

Temporary supply unit.

Restrictive conductive location.

Street furniture.

Testing.

Ring final circuit.

Supplementary insulation.

Thermal storage floor heating system.

Safety service.

Supplier

Triplen harmonics.

Sauna.

Surge current, {534}.

Trunking

SELV (separated extra-low voltage).

Surge protective device (SPD), {534}.

Verification.

Selectivity

Switch.

Voltage, nominal.

Shock

Switch, linked.

Extra-low.

Shock current.

Switch-disconnector.

Low.

Short-circuit current.

Switchboard.

High.

Short-circuit current under standard test conditions Isc STC.

Switchgear.

Voltage, reduced

System.

Voltage band

Show. Simple separation. Simultaneously accessible parts. Skilled person (electrically). Socket-outlet. Spur. Stand. Standard test conditions (STC).


TN system.

Band I

TN-C system.

Band II

TN-S system.

Voltage protection level (Up), {534}.

TN-C-S system.

Wiring system.

TT system. IT system. Multiple source and d.c. systems Temporary electrical installation. Page | 42

17th Edition Training Manual It is well worth taking a good amount of time to read through the Definitions. Don’t attempt to memorize them, but familiarity will help you quickly locate answers to questions on the Definitions section in the exam.

electrical energy other than a neutral conductor, a protective conductor or a PEN conductor. The term also means the equivalent conductor of a d.c. system unless otherwise specified in the Regulations.

Significant regulations new to 17th Edition

Definitions relating to personnel

Definitions relating to current

It is important you fully understand the difference between: Overcurrent A current exceeding the rated value. For conductors the rated value is the current-carrying capacity Overload An overcurrent occurring in a circuit which is electrically sound Fault current A current resulting from a fault Earth fault current A current resulting from a fault of negligible impedance between a line conductor and an exposed-conductive-part or a protective conductor

The definition of Competent person no longer applies. Instead new definitions are introduced which more accurately define the nature of skills and competency. Skilled person (electrically) Person who possesses, as appropriate to the nature of the electrical work to be undertaken, adequate education, training and practical skills, and who is able to perceive risks and avoid hazards which electricity can create. Instructed person (electrically) Person adequately advised or supervised by a skilled person (as defined) to enable that person to perceive risks and to avoid hazards which electricity can create.. Ordinary person Person who is neither a skilled person nor an instructed person.Other significant new definitions

Short-circuit current An overcurrent resulting from a fault of negligible impedance between live conductors having a difference in potential under normal operating conditions

Auxiliary circuit. Circuit for transmission of signals intended for control, detection, supervision or measurement of the functional status of a main circuit.

Line conductor. A conductor of an a.c. system for the transmission of

Low voltage switchgear and controlgear assembly. Combination of one or more low voltage switching devices together with associated control, measuring, signalling,


Page | 43

17th Edition Training Manual protective, regulating equipment, etc., completely assembled under the responsibility of the manufacturer with all the internal electrical and mechanical interconnection and structural parts. The components of the assembly may be electromechanical or electronic. The assembly may be either type-tested or partially type-tested (see BS EN 601439-1).

Extraneous-conductive-part The important definition for an Extraneous-conductive-part remains unchanged:

Electric vehicle (EV) Definitions relating to electric vehicles: charging points, modes of charging and vehicle connectors and couplers

Equipotential The term ‘equipotential’ is still used within BS 7671 and can be seen in ‘equipotential bonding’ and ‘protective equipotential bonding’

Medical Locations Definitions relating to medical locations and equipment

Changed definitions

The definition for an Exposed-conductive-part has changed from: ‘A conductive part of equipment which can be touched and which is not a live part but which may become live under fault conditions’ to: ‘Conductive part of equipment which can be touched and which is not normally live, but which can become

‘A conductive part liable to introduce a potential , generally Earth potential, and not forming part of the electrical installation’

NOTE: The previous (undefined) term of main equipotential bonding conductor is now replaced with the (defined) term: protective bonding conductor

Section summary This chapter has introduced the new definitions included in 17th Edition Wiring Regulations. You have learnt the importance of the definition of Line and the definitions for different currents and personnel. You have also learnt that some definitions have remained but carry revised wording.

live when basic insulation fails’


Page | 44


PART 2 - DEFINITIONS - TYPES OF SYSTEM & EARTHING ARRANGEMENTS AND VOLTAGE TERMS

Section Objectives

Earthing Systems

This short section introduces definitions relating to systems and earthing arrangements and voltage terms. Earthing systems will be discussed and illustrated in full later on in the course.

Five electrical systems are recognized by BS 7671 17th Edition Wiring Regulations. These are:


•

TN-S

•

TN-C

•

TN-C-S

•

TT

•

IT Page | 45

17th Edition Training Manual The SUPPLY system earthing arrangement is indicated by the first letter and signifies one or more points directly connected to Earth. (‘T’ stands for ‘terre’, French for Earthed) The INSTALLATION earthing arrangements are indicated by the second letter T Indicates that the exposed-conductive-parts of the installation are directly connected to Earth. N Indicates that the exposed-conductive-parts of the installation are directly connected to the earthed point of the source of energy. (‘N’ represents ‘neutre’ — neutral) The SYSTEM PROTECTIVE AND NEUTRAL CONDUCTOR arrangements are indicated by the following letters. S Separate neutral and protective conductors are provided. (‘S’ is for‘separee’—separate). C Implies that the Neutral and protective functions are both performed by single conductor, called a combined protective and neutral (PEN) conductor. (‘C’ stands for‘commune’— combined)


TN-S (TerreNeutre-Separee)

For a TN-S system, means shall be provided for the main earthing terminal of the installation to be connected to the earthed point of the source of energy. (Part of the connection may be formed by the distributor’s lines and equipment).

TN-C-S (TerreNeutre-Commune-Separee)

For a TN-C-S system, where protective multiple earthing is provided, means shall be provided for the main earthing terminal of the installation to be connected by the distributor to the neutral of the source of energy.

TT and IT

For a TT or IT system, the main earthing terminal shall be connected via an earthing conductor to an earth electrode complying with Regulation 542-2.

TN-C

The TN-C system is uncommon in the United Kingdom Neutral and protective functions are combined in a single conductor (a PEN conductor) throughout the system (although, the term CNE is sometimes used for such a conductor forming part of the distributor’s lines). The exposed-conductive-parts of the installation are connected to the PEN conductor, and hence to the earthed point of the source of. Regulation 8(4) of the Electricity Safety, Quality and Continuity Regulations 2002 prohibits the use of PEN conductors in consumers’ installations.

Page | 46

17th Edition Training Manual Definitions Relating to Voltage Terms

covered in detail in Sections 411 and 414 of the Regulations

Nominal voltage ranges (rms values for a.c.) are defined as:

Extra-low

Not exceeding 50 V a.c. or 120 V ripple-free d.c., whether between conductors or to Earth

Low

Exceeding extra-low voltage but not exceeding 1000 V a.c. or 1500 V d.c. between conductors or 600 V a.c. or 900 V d.c. between conductors and Earth

High

Normally exceeding low voltage

Voltage bands relating to nominal voltage categories

Fig. 10 Extra low voltage - Band I, telephone wiring (not part of BS7671)

BandI

Installations where protection against electric shock is provided under certain conditions by the value of voltage. Installations where the voltage is limited for operational reasons (e.g. telecommunications, signaling, bell, control and alarm installations). Extra-low voltage (ELV) will normally fall within Band I.

Band II

The voltages for supplies to household, and most commercial and industrial installations. Low voltage (LV) will normally fall within Band II.

Fig. 11 Low voltage - Band II, domestic wiring (BS7671)

SELV, PELV, FELV, and reduced low voltage are terms


Page | 47


PART 2 - DEFINITIONS - EXTERNAL INFLUENCE AND INTERNATIONAL PROTECTION CODE (IP CODE)

Section Objectives The aim of Lesson 7 is to introduce the concepts of alphanumeric codes which are used in the electrotechnical industry. The codes follow logical patterns and are used to identify levels of protection and influence for electrical equipment.

External Influence External Influence is defined as any influence external to an electrical installation which affects the design and safe operation of that installation The main references to external influences in BS 7671:2008 are Regulation Group 512.2, Section 522 and Appendix 5. Appendix 5 gives the classification and codification for external influences. Categories are identified by two letters and then a number (e.g. AD6).


Page | 48

17th Edition Training Manual The first letter signifies the general category of external influence, either:

Category

Code

Description

Environment (A)

AJ

Other mechanical stresses

AK

Flora (plants)

AL

Fauna (animals)

AM

Radiation

AN

Solar (sunlight)

The second ‘A’ relates to Ambient Temperature.

AP

Seismic (earthquakes)

The ‘5’ relates to an ambient temperature in the range of +50 C to + 400 C.

AQ

Lightning

Category

Code

Description

AR

Wind

Environment (A)

AA

Ambient temperature

BA

Capability(such as physical handicap)

AB

Humidity

BB

Resistance

AC

Altitude

BC

Contact with earth

AD

Water

BD

Evacuation (such as difficult)

AE

Foreign bodies

BE

Materials (fire risk)

AF

Corrosion CA

Materials (combustible or nonflammable)

CB

Structure (spread of fire etc.)

A — Environment B — Utilization C — Construction of buildings Taking the code AA5 as an example: The first letter ‘A’ signifies this classification relates to Environment.

AG

Impact

AH

Vibration

Utilisation (B)

Building (C)

Table 1 External influence codes


Page | 49

17th Edition Training Manual International Protection Code

Fig. 12 IP236S - Protection against solid bodies > 12.5mm (ie finger), water sprayed up to 60 Deg from vertical, 20 joule impact and manufacturer specific


Page | 50

17th Edition Training Manual The IP Code, Ingress Protection Rating, sometimes also interpreted as International Protection Rating, classifies and rates the degree of protection provided in mechanical casings and with electrical enclosures against •

the intrusion of solid objects (including body parts like hands and fingers),

•

dust,

•

accidental contact

•

water

There is some correlation between some external influence classifications and IP Codes.

What are IP Codes/Ratings

IEC (International Electro technical Commission) Publication 60529 Classification of Degrees of Protection Provided by Enclosures provides a system for specifying the enclosures of electrical equipment on the basis of the degree of protection provided by the enclosure The European standard is based on IEC529, which in Europe is EN 60529. In the UK this standard is prefixed with BS (British Standard). The Ingress Protection/International Protection Code (IP) ratings are developed by the European Committee for Electro Technical Standardization (CENELEC) and specify the environmental protection an enclosure provides. The IP rating normally has two (or three) numbers: Protection from solid objects or materials

Protection against mechanical impacts (commonly omitted) The rating refers to the equipment's ability to permit solids and liquids to penetrate the equipment enclosure. Electrical equipment’s IP rating is expressed as a two-digit number. The first number designates protection from solids, while the second number designates protection from liquids. It is important that manufacturers have their equipment certified by an outside laboratory to verify the product's IP rating. Epsilon is one such organization, which can verify the equipment’s IP rating; there are other companies that provide this service. The important thing is that the product is certified by an outside organization. If IP ratings are specified on a product's data sheet, then an approval certification number should also be included. An "X" is used for one of the digits if there is only one class of protection; i.e. IPX4 which addresses liquids only.

First Figure

The first digit of the IP code indicates the degree that persons are protected against contact with moving parts (other than smooth rotating shafts, etc.) and the degree that equipment is protected against solid foreign bodies (dusts) intruding into equipment.

Second Digit

The second digit indicates the degree of protection of the equipment inside the enclosure against the harmful entry of water or moisture (e.g. dripping, spraying, submersion, etc.).

Protection from liquids


Page | 51

17th Edition Training Manual 1stFigure - Protection against Solids IP

Test

Comment

0

No protection

1

Protected against solid bodies greater than 50mm diameter. (e.g. accidental contact with the hand)

2

Protected against solid bodies greater than 12.5mm diameter. (e.g. finger)

3

Protected against solid bodies greater than 2.5mm diameter (e.g. tools, wires)

IP

4

Test

Comment

Protected against solid bodies greater than 1.0mm diameter (e.g. thin tools and fine wire).

5

Protected against dust (no harmful deposit)

6

Completely protected against dusts

Dust Proof

Dust Tight

Table 2 IP Code - Protection against solids


Page | 52

17th Edition Training Manual 2nd Figure - Protection against Moisture IP

Test

Comment

IP

Test

Comment

0

No protection

1

Protected against vertically falling drops of water (condensation)

5

Protected against jets of water from all directions

2

Protected against drops of water falling up to 15° from the vertical

6

Protected against powerful jets of water from all directions

3

Protected against water sprayed up to 60° from the vertical

7

Protected against the effects of temporary immersion in water

8

Protected against the continuous effects of immersion in water having regard to specific conditions

4

Protected against splashing water from all directions

Table 3 IP Code Protection against moisture


Page | 53

17th Edition Training Manual The next table shows the particle size used in the first digit of the IP code. Although this table is not an accurate scale representation it gives an indication of the relative sizes of the solids. IP1X= 50mm

IP2X= 12.5mm

IP3X= 2.5mm

IP4X= 1mm

.

IP5= Dust

.

Table 4 Representation of sizes of solids of IP Code, first figure

Definitions Summary In these three sections we reviewed some of the more important definitions contained in Part 2, Definitions. Although Definitions covers just 4% of the 2382-15 Exam, it is a critical area of electrical knowledge. You should have read and understood every definition listed in the Regulations. It is vitally important to understand each definition as outlined in the 17th Wiring Regulations themselves.


Page | 54

17th Edition Training Manual REVIEW QUESTIONS – Definitions

Question 1

Question 3

A device other than current-using equipment, associated with such equipment or with the wiring of an installation is called

Path to follow for access to a safe area in the event of emergency is called A.

escape route

A.

not current-using equipment

B.

escape path

B.

accessory

C.

emergency route

C.

supplementary

D.

emergency path

D.

additional equipment

Question 2 The interface between the fixed installation and a heating unit is called

Question 4 External influence is any influence external to an electrical installation which A.

causes the installation to stop working

B.

affects the design and safe operation of that installation

thermal isolation

C.

affects working parameters of that installation

cold tail

D.

must be taken into account by the installation designers

A.

heat protection

B.

heating connection

C. D.


Page | 55


Question 8

The maximum current rating of a power track system is

A fault is defined as

A.

50 A

B.

63 A

A. a circuit condition in which current flows through an abnormal or unintended path

C.

78 A

B.

electric shock under overload conditions

D.

110 A

C.

electric shock under fault free conditions

D.

electric shock under overcurrent conditions

Question 6 Maximum demand and diversity should be determined before an installation is to begin A. to enable the REC to prepare the correctly rated supply

Question 9 Protection against electric shock under fault free conditions is known as A.

fault protection

B.

the customer needs the correct information

B.

indirect contact

C.

as it is a requirement of the REC

C.

basic protection

D.

for economic and reliable design

D.

direct contact

Question 7

Question 10

SELV denotes an extra low voltage system that is

Low voltage is defined as having a value which does not exceed

A.

centre tapped to the general mass of the earth

B. electrically separated from the general mass of the earth C. connected to the earth on the secondary of the transformer

A.

50v a.c.

B.

230v a.c.

C.

240v a.c.

D.

1000v a.c.

D. designed so as to avoid an electric shock between live conductors


Page | 56


ANSWERS – Definitions 1B, 2D, 3A, 4B, 5B, 6D, 7B, 8A, 9C, 10D,


Page | 57


MODULE 4 - PART 3 — ASSESSMENT OF GENERAL CHARACTERISTICS

Section Overview This is a short section which contains the guidance required for the assessment of general characteristics of each installation. By the end of the module you should be able to state the maintainability and compatibility requirements and how each characteristic of each installation should be designed to meet the compatibility and maintainability requirements.


Pay particular attention to: •

Determination of supply characteristics

•

Division of installation into circuits

You should also be able to identify and classify the external influences that dictate the selection and installation of equipment and be able to identify the characteristics of the source of power to each installation and how they are integrated into each installation.

Page | 58

17th Edition Training Manual The following characteristics of an installation should be assessed: •

The purpose for which the installation is intended to be used, its general structure and it supplies

•

The external influences to which it is to be exposed

•

The compatibility of its equipment

•

Its maintainability

•

Recognized safety services

Assessment for continuity of service

Ch31 -Purpose, Supplies & Structure 311 Maximum demand and diversity Regulation 311.1 has been reworded to:For economic and reliable design of an installation within thermal limits and admissible voltage drop, the maximum demand shall be determined. In determining the maximum demand of an installation or part thereof, diversity may be taken into account. 312 Conductor arrangement and system earthing Understand codes earthing systems codes: First letter identifies relationship of the power system to Earth: T - direct connection of one point to Earth; I - all live parts isolated from Earth, or one point connected to Earth through a high impedance. Second letter identifies relationship of the exposedconductive-parts of the installation to Earth: © 2008-2015 Electacourse

T - direct electrical connection of exposed-conductive-parts to Earth, independently of the earthing of any point ofthe power system; N - direct electrical connection of the exposed-conductiveparts to the earthed point of the power system (in a.c. systems, the earthed point of the power system is normally the neutral point or, if a neutral point is not available, a line conductor). Subsequent letter(s) (if any) – Arrangement of neutral and protective conductors: S– Protectivefunctionprovidedbyaconductorseparatefromthene utralconductororfromtheearthedline(or,in a.c. systems, earthed phase) conductor. C– neutralandprotectivefunctionscombinedinasingleconductor( PENconductor) 313 Supplies 313.1 The following characteristics of the supply or supplies, from whatever source, and the normal range of those characteristics where appropriate, shall be determined by calculation, measurement, enquiry or inspection: •

The nominal voltage(s)

•

The nature of the current and frequency

•

The prospective short-circuit current at the origin of the installation

•

The earth fault loop impedance of that part of the

Page | 59

17th Edition Training Manual •

system external to the installation

from the failure of a single circuit such as a lighting

The suitability for the requirements of the

circuit.

installation, including the maximum demand •

residual current devices (RCDs) due to excessive

device(s) acting at the origin of the installation.

protective conductor currents produced by

•

Supply

•

Number and type of live conductors

•

Earthing arrangement

313.2 Supplies for safety services and standby systems. Where the provision of safety services is required, their supplies should be separately assessed. Typical systems are: •

Emergency lighting systems,

•

Sprinkler systems,

•

Generators,

•

Smoke extract system etc.

314 Division of installation Every installation shall be divided into circuits, as necessary, to: Avoid danger and minimize inconvenience in the event of a fault. • •

Reduce the possibility of unwanted tripping of

The type and rating of the overcurrent protective

The characteristics of the following also need to be ascertained:

•

•

equipment in normal operation. •

Mitigate the effects of EMI (electromagnetic disturbances)

•

Prevent the indirect energizing of a circuit intended to be isolated.

Separate circuits shall be provided for parts of the installation, which need to be separately controlled, in such a way that those circuits are not affected by the failure of other circuits. The number of final circuits, with each final circuit connected a separate way in a distribution board, should comply with the standards for overcurrent protection (BS7671 Chapter 43), isolation and switching (Section 537), and current carrying capacities of conductors.

Ch32 - Classification of External Influences The external influences that determine the selection of equipment and installation methods/techniques are defined in Appendix 5 and are classified as follows:

(see also Section 537).

Each condition of external influence is designated by a code comprising a group of two capital letters and a number.

Take account of danger or hazards that may arise

The first letter relates to the general category of external

Facilitate safe inspection, testing and maintenance


Page | 60

17th Edition Training Manual influence: A – Environment

•

Earth leakage current

•

Excessive protective conductor currents not due to a fault.

B – Utilization C – Construction of buildings The second letter relates to the nature of the external influence: A, B, C, D…..S The number relates to the class within each external influence: 1, 2, 3, 4 For example, the code AA4 signifies: A

= Environment

AA

= Environment – Ambient temperature

AA4 = Environment – Ambient temperature in the range of -5° C to + 40° C See table in previous module

Ch33 - Compatibility of Characteristics An assessment shall be made of all characteristics of equipment that are likely to have harmful effects upon other electrical equipment or other services or likely to impair the supply. Those characteristics include:

•

d.c. feedback

•

High-frequency oscillations

•

Necessity for additional connections to earth

•

Power factor

332.1 Electromagnetic Compatibility

332.1 has been modified; it no longer refers to installations but only to equipment.All electrical equipment forming part of an electrical installation shall meet the appropriate electromagnetic compatibility(EMC) requirements and shall be in accordance with the relevant EMC standard.

Ch 35 - Safety Services Chapter 35 adds requirements for safety services, which recognizes the need for safety services as they are frequently regulated by statutory authorities whose requirements have to be observed. e.g. emergency escape lighting, fire alarm systems, installations for fire pumps, fire brigade lifts and smoke and heat extraction equipment.Sources for safety services should be separately assessed.The following sources are recognized:

•

Transient overvoltages

•

Undervoltage

•

Storage batteries

•

Unbalanced loads

•

Primary cells

•

Rapidly fluctuating loads

•

Independent generator sets

•

Starting currents

•

Separate feeders

•

Harmonic currents


Page | 61

17th Edition Training Manual Ch 36 - Continuity of Service Chapter 36, Continuity of Service, requires that an assessment shall be made for each circuit of any need for continuity of service considered necessary during the intended life of the installation. These characteristics shall be ascertained for an external supply and shall be determined for a private source. These requirements are equally applicable to main supplies and to safety services and standby supplies. If the provision of safety services is required, and/or standby supplies is required by the person specifying the installation, the characteristics of the source or sources of supply for safety and/or standby systems shall be separately assessed. Such supplies shall have adequate capacity, reliability and rating and appropriate change over time for the operation specified. Further details are contained in Chapter 56.


Page | 62

17th Edition Training Manual REVIEW QUESTIONS – Assessment of General Characteristics

Question 1

Question 3

Which of the following should be taken into account in the choice of methods of protection for safety and the selection and erection of equipment?

A system which has only one point directly earthed at the source, the exposed-conductive-parts of the installation(s) being connected to earth electrodes electrically independent of the earth electrode of the supply system (the source earth) is

A.

It's maximum power

B.

Its maintainability

C.

It's suitability for public service

D.

The country of origin

Question 2 Which of the following are NOT referred to in the regulations as current-carrying conductors in a.c. circuit under normal operating conditions

A.

TT system

B.

NN system

C.

NT system

D.

TN system

Question 4

A.

Two-phase 3-wire

The second letter of the code for system earthing type has a meaning of

B.

Three-phase 3-wire

A.

Relationship of the power system to Earth

C.

Three-phase 4-wire

B.

Arrangement of neutral and protective conductors

D.

Two-phase 4-wire

C.

Relationship of the exposed-conductive-parts of the installation to Earth

D.

Relationship of the exposed-conductive-parts of the installation to the power system


Page | 63


Question 5

Question 7

The third letter of the code for system earthing type has a meaning of

Electrical installations shall be divided into circuits to A.

allow for more socket outlets

A. Relationship of the exposed-conductive-parts of the installation to Earth

B.

reduce power usage

B. Relationship of the exposed-conductive-parts of the installation to the power system C.

Relationship of the power system to Earth

D.

Arrangement of neutral and protective conductors

Question 6

C. allow for expansion without changing the maximum demand D. minimise inconvenience in the event of a fault condition

Question 8

Electrical installations shall be divided into circuits to

Identify which of the following forms part of the assessment of general characteristics

A.

allow easier access to the installation

A.

distribution circuits

B.

allow more even distribution of power

B.

switchgear requirements

C.

allow for expansion without changing the maximum demand

C.

diversity

D.

recognised safety services

D.

reduce electromagnetic interference


Page | 64


Question 10

Electrical installations should be divided into circuits where necessary in order to

A two story house should have at least two lighting circuits in order to

A.

prevent the indirect energizing of a circuit intended to be isolated

A.

reduce the load on a consumer circuit

B.

allow for fluorescent luminaires

B.

prevent harmonic currents

C.

C.

ensure at least one socket outlet is available in the event of a fault

be split across the RCD protected part of the consumer unit

D.

minimise danger in the event of a fault

D.

avoid unbalanced loads

ANSWERS – Assessment of General Characteristics 1B, Ref: BS7671: 301.1 2D, Ref: BS7671: 312.1.1 3A, Ref: BS7671: 312.2.2.1 4C, Ref: BS7671: 312.2 5D, Ref: BS7671: 312.2 6D, Ref: BS7671: 314.1 7D, Ref: BS7671: 314.1 8D, Ref: BS7671: 301.1 9A, Ref: BS7671: 314.1 10D, Ref: BS7671: 314.1


Page | 65


MODULE 5 - PART 4 — PROTECTION FOR SAFETY

Overview

Ch41 - Protection Against Electric Shock

Part 4 contains four Chapters, which are:

410 — Protection against electric shock

Chapter 41:

Protection against electric shock

Chapter 42:

Protection against thermal effects

Chapter 43:

Protection against overcurrent

Chapter 44: Protection against voltage disturbances & electromagnetic disturbances


This chapter deals with protection against shock applied in electrical installations. It is based on BS EN 61140, which applies to the protection of persons and livestock, has a fundamental rule that hazardous-live-parts shall not be accessible and conductive live parts shall not be hazard-live, either in use without a fault or in single-fault conditions.

Page | 66

17th Edition Training Manual Protection is required against two types of hazard: •

Protection in use without a fault (now designated as basic protection), known previously as

Additional protection can be provided by: Residual current devices (RCDs), and/or Supplementary bonding

protection against direct contact in the 16th Edition (BS 7671:2001). •

Protection under fault conditions (now designated as fault protection), known previously as protection against indirect direct contact in the 16th Edition (BS 7671:2001).

Basic protection–is protection against something that is intentionally meant not to be LIVE. Fault protection–is protection against something that is LIVE through a fault. e.g. water pipe, metal casing. Basic protection relates to protection under fault free conditions. Basic protection is covered in Section 416 of BS 7671.

Fig. 13 RCD with test button

A person (or livestock) can receive a shock in one of two ways: •

Contact with a live part whilst in contact with Earth

•

Contact with live parts at different potentials

410.3.2 — In addition to basic and fault protection, ‘additional protection’ is required under specified conditions of external influence and in certain special locations covered in Part 7 of BS7671:2008


Fig. 14 Supplementary bonding across the stop-cock

Page | 67

17th Edition Training Manual 410.3.3 — There are four main protective measures in Chapter 41: •

Automatic disconnection of supply (Section 411)

•

Double or reinforced insulation (Section 412)

•

Electrical separation for the supply to one item of current-using equipment (Section 413)

•

Extra-low voltage provided by SELV or PELV(Section 414)

Each protective measure has to consist of: An appropriate combination of a provision for basic protection and an independent provision for fault

Shall be only installed in installations where it is under the supervision of a skilled or instructed person so that unauthorized changes cannot be made

411 — Protective measure Automatic Disconnection of Supply Automatic disconnection of supply (‘ADS’ for short) is the most commonly used protective measure. This measure of protection is used in virtually every electrical installation. Basic protection for ADS can be provided by either: •

Basic insulation

•

Barriers or Enclosures

protection, OR An enhanced protective provision whichprovides both basic protection and fault protection. 410.3.4 — For special installations or locations, additional protectivemeasures specified in Part 7 shall be used. 410.3.5 — The protective measure of placing out of reach, as specified in 417 shall only be used in installations where access is restricted to Skilled, orInstructed persons under the supervision of skilled persons 410.3.6 — The protective measures in 418 i.e. •

Non conducting location

•

Earth-free local equipotential bonding

•

Electrical separation


Fig. 15 Electrical cabinet providing basic protection

Page | 68

17th Edition Training Manual Fault protection is provided by the combination of: •

Protective earthing of installation exposedconductive-parts

•

Protective equipotential bonding of extraneousconductive-parts

•

Automatic disconnection of supply by a protective device(e.g. fuse, circuit-breaker or RCD)

ADS earthing and bonding requirements for TN systems (411.4), TT systems (411.5), IT systems (411.6), Functional extra-low voltage (FELV) (411.7), Reduced low voltage systems (411.8) and Earthing systems were covered previously in Part 2 refer back for revision if necessary. The requirements of Chapter 54 Earthing arrangements and protective conductors may also need to be consulted. Structural parts which may provide earthing could include: •

Water installation pipes

•

Gas installation pipes

•

Other installation pipes and ducting (such as incoming pipe-work from an oil tank)

•

Central heating and air conditioning systems

•

Exposed metallic parts of the building structure

•

Lightning protective systems (in accordance with BS EN 62305)Explanation of ADS – Basic circuit concept Earth loop path:Basic circuit concept (earth fault loop path) Fig. 16 Examples of earthing to structural parts


Page | 69

17th Edition Training Manual The current path

Line conductor from transformer winding to point of use. Returned back to the Neutral conductor Then to the Neutral point at the transformer winding. Via the supply meter, distribution board and local switching.

Fig. 17 Current path TN-S System


Page | 70

17th Edition Training Manual The fault current path

Line conductor from transformer winding to point of use / fault From the earth casing of the appliance to the Cpc of circuit Earthing terminal of Distribution board Steel armouring of SWA cable Earthing terminal of Supply Isolator Main Earthing Conductor Main Earthing Terminal Supply Company’s Earth (Sheath of Cable) Earthed – Neutral point at the transformer Transformer winding Or unfortunately Through the body of the user to the point of contact with the Earth

Fig. 18 Fault current path - TN-S System


Page | 71

17th Edition Training Manual Maximum disconnection times

411.3.2 — Automatic disconnection in case of a fault. 50 V < UO ≤ 120 V 120 V < UO≤ 230 V

System

230 V < UO ≤ 400 V

UO> 400 V

A.C.

D.C.

A.C.

D.C.

A.C.

D.C.

A.C.

D.C.

TN

0.8

Note

0.4

5

0.2

0.4

0.1

0.1

TT

0.3

Note

0.2

0.4

0.07

0.2

0.04

0.1

Table 5 BS7671 Table 41.1 (page 53)

411.3.2.2 — Maximum disconnection time limited to: 0.4 second for TN system final circuits NOT exceeding 32 A and 0.2 second for TT systems.

labelled socket-outlet, or where a documented risk assessment determines that RCD protection is not necessary.

411.3.2.3 — In a TN system, a disconnection time not exceeding 5 seconds is permitted for distribution circuits and for circuits ≥32 A.

In a.c. systems, additional protection by means of an RCD in accordance with Regulation

411.3.2.4 — In a TT system, a disconnection time not exceeding 1 second is permitted for distribution circuits and for circuits ≥32 A.

411.3.3 — Additional protection

Reference to ordinary persons in Regulation 411.3.3 has been deleted. The regulation now requires RCD protection in accordance with Regulation 415.1 for socket-outlets up to 20 A (and for mobile equipment up to 32 A for use outdoors) for all installations. However, there is an exception for RCD protection (for socket-outlets up to 20 A) for a specific


411.3.3 Additional protection

415.1 shall be provided for: i)

socket-outlets with a rated current not exceeding 20 A, and

ii) mobile equipment with a current rating not exceeding 32 A for use outdoors. An exception to (i) is permitted: a) where, other than for an installation in a dwelling, a documented risk assessment determines that the RCD protection is not necessary, or b) for a specific labelled or otherwise suitably identified

Page | 72

17th Edition Training Manual socket-outlet provided for connection of a particular item of equipment.

apply to FELV systems according to Regulation 411.7 or reduced low voltage systems according to Regulation 411.8. NOTE 3: See Appendix 2, item 10 in respect of risk assessment

NOTE 1: See also Regulations 314.1(iv) and 531.2.4 concerning the avoidance of unwanted tripping. NOTE 2: The requirements of Regulation 411.3.3 do not

Example

411.3.3 (b) can apply for installations other than dwellings A risk assessment must be attached to the electrical installation certificate or minor electrical installation works certificate Table 6 Requirements for documented risk assessment

RCD not exceeding 30 mA

Documented risk assessment

Specifically labelled socket outlet

Domestic

YES

NO

YES

Commercial/Industrial

YES

YES

YES

Type of property

The HSE risk assessment follows a 5-step method Step 1

Identify the hazard

Step 2

Identify who is at risk

Step 3

Evaluate the risk

Step 4

Report your findings

Step 5

State when the assessment is to be reviewed


Page | 73

17th Edition Training Manual Table 7 Risk assessment template

Hazard

Who’s at risk

Likelihood of injury

Severity of injury

Risk Level

Existing control measures

New control measures

Review date

Electric shock

Ordinary persons

1

7

Low

Insulation, Barriers & Enclosures

Signs & Labels

Quarterly

Formula for calculating Risk Level

Risk Level = (Likelihood or injury + Severity of injury) / 2 [(1 + 7) / 2 = 4] 4 = Low risk level Example of code for Likelihood or injury + Severity of injury Low 1 – 4 | Medium 5 – 8 | High 9 – 10

Chapter 41 - Protection against electric shock Regulations 411.4.5, 411.5.4 and 411.6.4 now include a Cmin factor. Maximum earth fault loop impedances given in Tables 41.2,


41.3, 41.4 and 41.6 have been revised to take account of the Cmin factor given in CLC/TR 50480:2011. Cmin is the minimum voltage factor to take account of voltage variations

Page | 74

17th Edition Training Manual depending on time and place, changing of transformer taps and other considerations. Also, the notes to the Tables have been changed in connection with maximum permitted operating temperature.

been reduced by 0.05% to take into account’ voltage variations depending on time and place, changing of transformer taps and other considerations’.

Maximum earth fault loop impendence values (Zs) have

BS 7671 Appendix 2 section 14 Effective dates

Nominal voltage

Permitted tolerance

Permitted voltage range

Pre-1995

240 V

+6 % / −6 %

225.6 – 254.4 V

1 Jan. 1995

230 V

+10 % / −6 %

216.2 – 253.0 V

Table 8 Voltage variation

How to use Cmin

Uo = Nominal a.c. rms line voltage to earth Zs = Earth fault loop impedance

Example

(using BS EN 60898 Type B circuit breaker values) Ia = 160 A (Appendix 3 Fig. 3A4)

Ia = Current causing automatic operation of protective device with the stated time

Uo = 230 V Zs = 1.44 Ω (Table 41.3)

Cmin = 0.95 Cmin = minimum voltage factor to take account of voltage variations depending on time and place, changing of transformer taps and other considerations.

Zs = Uo / Ia

Formula in BS 7671

1.44 Ω = 230 V / 160 A

Transposed

Zs × Ia ≤ Uo × Cmin Zs ≤ (Uo x Cmin ) / Ia

Cmin = 0.95

Zs x Cmin = New tabulated Zs values contained in BS 7671 Amendment 3 1.44 = 0.95 = 1.37 Ω


Page | 75

17th Edition Training Manual 411.3.2.3.Where an RCD is used this current is the rated residual operating current providing disconnection in the time specified in Table 41.1 or Regulation 411.3.2.3.

where: Zs is the impedance in ohms (Ω) of the fault loop comprising:

Uo is the nominal a.c. rms or d.c. line voltage to Earth in volts (V).

 the source  the line conductor up to the point of the fault, and

Cmin is the minimum voltage factor to take account of voltage variations depending on time and place, changing of transformer taps and other considerations.

 the protective conductor between the point of the fault and the source. Ia is the current in amperes (A) causing operation of the protective device within the time specified in Table 41.1 of Regulation 411.3.2.2 or, as appropriate, Regulation Table 41.3

Maximum earth fault loop impedance (Zs) for circuit-breakers with Uo of 230 V, for operation giving compliance with the 0.4 s disconnection time of Regulation 411.3.2.2 and 5 s disconnection time of Regulation 411.3.2.3 (for RCBOs see also Regulation 411.4.9) (a) Type B circuit-breakers to BS EN 60898 and the overcurrent characteristics of RCBOs to BS EN 61009-1 Rating (amperes)

3

Zs (ohms)

6

10

7.28 14.57

16

20

2.73 4.37

25

32

1.75 2.19

40

50

1.09 1.37

63

80

0.69 0.87

100

125

0.44 0.55

0.35

Table 9 Zs values for circuits breakers

The IET On-site Guide and IET Guidance Note 3 will apply ‘rule of thumb’ to the New Tabulated Zs figures contained in BS 7671 BS 7671 states a maximum Zs figure of 1.37 Ω for a 32 A type B circuit breaker. The figure quoted in both the OSG and GN3 will be 1.37 x 0.8 = 1.10 Ω


Page | 76

17th Edition Training Manual 411.7 — Functional Extra Low Voltage FELV Where an extra-low voltage system does not meet all the requirements of a SELV or PELV system, supplementary provisions are required. Such an arrangement is known as FELV with protective requirements being generally the same as for low-voltage (e.g. 230/400 V) circuits.

voltage could appear in the event of a failure in the basic insulation of a live part.The measure generally applies to individual items of equipment, such as: •

Hand-held luminaires

•

Handheld portable appliances

•

Casing assemblies of switchgear and controlgear

411.8 — Reduced Low Voltage Systems Where for functional reasons the use of extra-low voltage is impracticable, a reduced low voltage system may be used.These systems are often used on construction and demolition sites, together with providing supplies to equipment in industrial installations: •

Nominal voltage between line and neutral, and between phases, is 110 V A.C. rms

•

Nominal voltages:

•

55 V to Earth for a single-phase system

•

63.5 V to Earth for a three-phase system

•

Maximum disconnection time of 5 seconds at all points of utilization

412 — Protective measure Double or reinforced insulation

The protective measure double or reinforced insulation relies on the use of equipment, meeting certain requirements and having no exposed metal parts on which a dangerous


Fig. 19 Example of a hand held portable appliance indicating live and protected parts

Where it is intended to use double or reinforced insulation as the sole protective measure in an installation it must be under effective supervision in normal use so that no change is made that would impair the effectiveness of the protective

Page | 77

17th Edition Training Manual measure. This protective measure provides: basic protection by the use of basic insulation and fault protection by the use of supplementary insulation.Or both basic and fault protection can be provided by reinforced insulation (between live parts and accessible parts).

Electrical equipment

Refer to Regulations 412.2.1.2 and 412.2.1.3, where electrical equipment has basic insulation only or uninsulated live parts.

Fig. 20 Do not connect to earth symbol

Following the application of supplementary or reinforced insulation applied in the process of erection the symbol ‘do not connect to earth’ should be fixed in a visible position on the exterior and interior of the enclosure.

•

The supply is electrically separate from all other systems and from Earth.

•

Shaver supply units complying with BS EN 615582-5 are one example of such a system.

Basic protection is provided by basic insulation of live parts, or barriers and enclosures, or double or reinforced insulation.Fault protection is provided by: Ensuring the separated circuit is supplied by a source with at least simple separation. Fig. 21 A transformer

Limiting the voltage of the separated circuit to not greater than 500 V.

Precautions being present to prevent live parts of the separated circuit from being in contact with any other circuit or Earth or to a protective conductor

413 — Protective measure Electrical separation

Electrical separation is commonly referred to as compartment trunking, this is mostly a misconception as electrical separation is where there are two supplies that are separate within the same enclosure e.g. a transformer.


Page | 78

17th Edition Training Manual 414 — ELV provided by SELV or PELV SELV — Separated extra-low voltage PELV — Protective extra-low voltage

single fault cannot give rise to the risk of an electric shock’ Requirements for both ‘basic’ and ‘fault’ protection are: •

Safety is achieved by:

Nominal voltage limits of 50 V A.C. and 120 V ripple-free D.C.

•

Limiting system voltage

•

Supply sources listed in 414.3.

•

Deriving supply from a specified source of energy

•

Requirement for compliance with Regulation

•

Specifying strict conditions relating to their installation and use.

Specified safety measures enable the systems to be suitable for use in most situations.

Group 414.4 is fulfilled NOTE: Additional ‘basic’ protection is required where the nominal voltage exceeds 25 V a.c. or 60 V d.c.

Note however some special installations or locations may require the maximum voltage to be limited and in some cases additional basic protection to be provided. Separation of circuits: •

Required between SELV and PELV circuits from all other circuits (other than other SELV and PELV circuits).

•

Requirement for basic insulation between SELV and PELV systems and all other SELV and PELV systems.

•

For SELV systems only, basic insulation is required between the SELV system and Earth

SELV is defined as: ‘An extra-low voltage system which is electrically separated from Earth and from other systems in such a way that a


Fig. 22 SELV protects the user from electric shock in the case of a fault

Page | 79

17th Edition Training Manual 415 — Additional Protection

In addition to basic protection and fault protection, ‘additional protection’ is required under certain conditions of external influence and in certain of the special locations covered in Part 7

417 — Obstacles and placing out of reach The protection by placing out of reach is intended to prevent unintentional contact with live parts.

Additional protection can be provided by: RCDs (specific requirement in some parts), or Supplementary bonding. 415.1 — Additional protection by RCD The use of RCDs with a rated residual operating current (I∆n) not exceeding 30 mA and an operating time not exceeding 40 ms at a residual current of 5 I∆n is recognized in a.c. systems as additional protection in the event of: ‘Failure’ of the provision for basic protection and/or the provision of fault protection, or Carelessness by users (e.g. penetrating a cable concealed in a wall or partition with a nail or screw, or cutting through a lead connected to a outdoor appliance. 415.2 — Supplementary bonding This is an additional protective provision used to enhance the standard fault protection system, as outlined in Chapter 41. It may be required where disconnection times cannot be met, or where required due to the special nature of the installation

Fig. 23 A common but not mandatory symbol for placing out of reach

Overhead lines are the most common to be within this criteria and are dealt with more by the Electricity Safety, Quality and Continuity Regulations 2002.

417.3.1 — A bare live part of an overhead line shall not be within arm’s reach or within 2.5m of: An exposed-conductive part An extraneous-conductive part A bare live part of any other circuit 418 — Protective measures for application only where the installation is controlled or under the supervision of skilled or instructed persons. The following fault protective provisions have limited use: •

Non-conducting location

•

Protection by earth-free local equipotential bonding


Page | 80


Electrical separation for the supply to more than one item of current-using equipment

•

Please refer to Section 418 of BS 7671:2008 for a more comprehensive description.

Ch42 - Protection Against Thermal Effects The existing regulations have been modified slightly and a new Section 424. Protection against overheating, has been added. A new Regulation 421.1.200 has also been included. Regulation 421.1.200 requires switchgear assemblies including consumer units to have their enclosure manufactured from non-combustible or not readily combustible material or be enclosed in a cabinet or enclosure constructed of non-combustible or not readily combustible material.

420 — Scope

To prevent people, livestock and property from the effects of arcing, sparking, overcurrents and many other risks of fire!

Fig. 24 The consequence of arcing can be serious

Detrimental thermal effects result from badly designed or incorrectly installed electrical equipment including: •

Harmful effects of heat or thermal radiation developed by electrical equipment.

•

Ignition, combustion or degradation of materials.

•

Flames and smoke (where a fire hazard could be propagated from an electrical installation to other nearby fire compartments.

•

Safety services being cut off by the failure of electrical equipment.


Page | 81

17th Edition Training Manual 421 — Protection against fire caused by electrical equipment 421.1.201

Within domestic (household) premises, consumer units and similar switchgear assemblies shall comply with BS EN 61439-3 and shall: i)

have their enclosure manufactured from noncombustible material, or

ii) be enclosed in a cabinet or enclosure constructed of non-combustible material and complying with Regulation 132.12. NOTE 1: Ferrous metal, e.g. steel, is deemed to be an example of a non-combustible material.

View You Tube interview with London Fire Brigade indicating reasons for changes to BS 7671 in 2015

https://www.youtube.com/watch?v=-AaKOx5q1j4 The draft of Amendment 3 proposes changes to the fire protection regulations in BS 7671 Wiring Regulations. If approved, these changes will be incorporated in the 17th Edition of the Wiring Regulations, due to be published in January 2015. Chief engineer Geoff Cronshaw interviews London Fire Brigade

Devastating effects of a consumer unit fire

NOTE 2: The implementation date for this regulation is the 1st January 2016, but does not preclude compliance with the regulation prior to that date.

What is driving this change to non-combustible consumer units?

Investigation into several fires involving plastic consumer units, by the London Fire Brigade, has concluded that a key cause of the fires was substandard cable connections made by the Electrician. These resulted in overheating, which eventually ignited the plastic enclosure. London Fire brigade report that there are on average 2 domestic fires per week due to consumer units. Loose and poor connection cause high resistance which in turn increases heat above manufacture recommendations.


The reason for the change is to contain a fire within the consumer unit and/or enclosure.

Page | 82

17th Edition Training Manual What impact will this regulation have?

Eventually all new consumer units installed in UK homes, i.e. within domestic (household) premises must have their enclosures manufactured from a non-combustible material, or be enclosed in a cabinet or enclosure constructed from a non-combustible material. This is likely to result in an increased use of metal enclosures.

What is meant by ‘within domestic (household) premises’?

It is understood that Regulation 421.1.200 applies to consumer units and similar switchgear assemblies to BS EN 61439-3 inside all domestic (household) premises including their integral/attached garages and outbuildings or those in close proximity.

Fig. 25 Consumer unit - all cables are to pass through the same entry/exit hole

When will Regulation 421.1.200 come into effect? Amendment 3 is intended to come into effect on 1st July 2015. Installations designed after 30th June 2015 are to comply with BS 7671:2008 incorporating Amendment 3, 2015.

However, Regulation 421.1.200 does not come into effect until the 1st January 2016 to allow manufacturers time to change their product ranges to comply.

Other consideration when using metal consumer units

As electromagnetic effects from incorrectly installed cables of alternating current (a.c.) circuits can cause heat, all cables are to pass through the same entry/exit hole


Fig. 26 A non-ferromagnetic metal or non-metallic entry plate is to be used

Page | 83


Fire propagating structures are used

•

Locations are of national, commercial, industrial or public significance

422.2 — Conditions for evacuation in an emergency BD2 — Low density occupation, difficult to evacuate (e.g. high-rise buildings) BD3 — High-density occupation, easy to evacuate (e.g. theatres, cinemas, etc) BD4 — High-density occupation, difficult to evacuate Fig. 27 Ferro-magnetic fixing plate may be used provided slots are cut in plate between conductors

(e.g. buildings open to the public, hospitals, hotels residential homes etc.) 422.3 — Locations with risks of fire

421.4 — Precautions must be taken against fire caused by electrical equipment located where heat may be focused onto a concentrated surface.

Risk of fire is increased due to the manufacture, processing or storage of flammable materials (BE2) Additional requirements also relate to:

Heat sources must be a suitable distance from adjacent materials or building elements.

422.4 — Building that are mainly constructed of combustible material, such as wood (CA2)

422 — Precautions where particular risks of fire exists

422.5.1 — Fire propagating structures

Section 422 contains additional requirements where particular risks of fire exist due to:

Where a building has a shape and dimension that facilitates the spread of fire (CB2); high-rise buildings (e.g. chimney or up draft effect):

Difficult conditions for evacuation and/or high

422.6 — Installations in locations of national,

density occupation

commercial, industrial or public significance.

•

The nature of processed or stored materials

Special measures and the installation of particular

•

Combustible construction materials used

cables in such locations may have to be considered.

•


Page | 84

17th Edition Training Manual These are locations, which are of national monuments, museums and other significant public buildings, i.e. railway stations, airports and visitor attractions fall within this criteria. Additional requirements where particular risks of fire exists and depending upon the particular risk (BD2, BD3, BD4, BE2, CA2 or CB2), consideration should be given to: •

Distances between electrical equipment and

A part intended to Metallic be touched but not Non-metallic hand-held

70*

A part which need Metallic not be touched for normal operation Non-metallic

80*

80*

90*

Table 10 BS7671 Table 42.1 - Temperature limit under normal load conditions for an accessible part of equipment within arm’s reach.

combustible materials

Protection against overheating

•

Maximum temperatures of electrical enclosures

•

The location of switchgear, and choice of wiring

•

Equipment such as motors, motor controls,

424 Protection Against Overheating is a new Section concerning the overheating of heating appliances. It stresses the importance of using British Standard equipment installed to the manufactures instructions.

luminaires, heating appliances etc. •

Overload and fault protective devices, & use of RCDs

423 — Protection against burns

Except where a Harmonized Standard specifies otherwise, electrical equipment within arm’s reach should not attain a temperature in excess of the appropriate limit.

Accessible part A hand-held part

Material of Maximum accessible surfaces temperature (0C) Metallic

55*

Non-metallic

65*


424.1 Forced air heating systems

Forced air heating systems shall be such that their heating elements, other than those of central storage heaters, cannot be activated until the prescribed air flow has been established and are deactivated when the air flow is less than the prescribed value. In addition, they shall have two temperature limiting devices independent of each other which prevent permissible temperatures from being exceeded in air ducts. Supporting parts, frames and enclosures of heating elements shall be of non-combustible material.

Page | 85

17th Edition Training Manual 424.2 Appliances producing hot water or steam

All appliances producing hot water or steam shall be protected by design or erection against overheating in all service conditions. Unless the appliances comply as a whole with the appropriate British Standards, the protection shall be by means of an appropriate non-self-resetting device, functioning independently of the thermostat. If an appliance has no free outlet, it shall also be provided with a device which limits the internal water pressure.

The side walls of radiant heaters which are not touched by the heat radiation should have a sufficient distance from flammable parts. In case of a reduction of the distance by an inflammable partition, this partition should have a distance of at least 1 cm to the enclosure of the radiant heater and to flammable parts. Radiant heaters shall be mounted so that in the direction of radiation a safety distance of at least 2 m from flammable parts is ensured unless otherwise declared by the manufacturer

Ch43 - Protection Against Overcurrent Chapter 43 describes how live conductors are to be protected by one or more devices for the automatic disconnection of the supply in the event of: Overload (Section 433) Fault current (Section 434) Protection against both of the above should be coordinated (Section 435) Fig. 28 Quooker, boiling water tap. An example of a new type of hot water producing appliance

424.3 Space heating appliances

The frame and enclosure of space heating appliances shall be of non-combustible material. NOTE: In operating areas with a fire risk, space heating appliances may not be operated if the air from these areas is guided through the appliance.


Section 436 covers situations where overcurrent is limited by the characteristics of the supply.Let us review the following definitions: •

Overcurrent, overload current and fault current

•

Short-circuit current

•

Earth fault current

….and because it is important, we refresh our understanding of currents:

Page | 86

17th Edition Training Manual What is the difference between an overload current and a fault current? What is the difference between a short-circuit current and earth fault current?

Overcurrent and fault current

An overcurrent situation, is one that a current exists that is larger (slightly) than the design operating current.

Overload current

An overload occurs when a current flows that is somewhat too high (usually 50% to 100% too high) for the system. Overloads don't normally cause immediate damage. Instead, the likelihood of damage increases gradually as the duration of the overload increases. If the fault is not resolved, cables will overheat and melt, exposing bare conductors. The heat generated may be sufficient to cause a fire. In a domestic setting, overloads usually result from using too many appliances at the same time, or plugging a heavyduty appliance into a supply that isn't strong enough for it.

Short-circuit current

A short-circuit current is a overcurrent, resulting from a fault of negligible impedance between Live conductors. A short-circuit is a connection between live and neutral, or between live and earth, that bypasses an appliance. The connection will probably have a low resistance, and the current that can flow may be hundreds or thousands of times too high for the system. This current is usually called the fault current or short-circuit current. A short-circuit will


by produced if, for example, the wires in a mains plug become loose and touch one another.

Earth fault current

An earth-fault current is an overcurrent resulting from a fault of negligible impedance between a Line conductor and exposed-conductive-part or a protective conductor What is the difference betweenan overload current and a fault current? What is the difference betweena short-circuit current and earth fault current? These questions are best answered by the following: Overcurrent - Is the name giving to all of the following conditions and could be classed as an integument Overload current - As previously described, the situation in which the current is larger than the designed operating current i.e. too many 3Kw loads inserted into a ring circuit at the same time resulting in the device to rupture or trip after a period of time Fault current - Is usually described as a short, large intake of current usually due to a fault Short-circuit current - Is caused when there is a fault between Live conductors with little or no resistance e.g. the Line and Neutral conductors touching together Earth fault current - Occurs when there is a connection with negligible resistance between Line or Neutral (Live) conductors and any connection to Earth

Page | 87

17th Edition Training Manual A nail inserted in a PVC sheathed cable accidentally could be either a Short-Circuit or a Earth fault current, as is water penetrating into a exterior luminaire. A common short-circuit is when trying to insert a light-bulb into a flex drop, the lamp-holder turns and, due to the conductors becoming bare both wires twist together. Unfortunately this fault is still very common: the consumer trying to retrieve the toast with a knife touching the casing of the toaster and the element.

Fig. 29 Overcurrent

431 — Protection of line conductors

432.4 — Characteristics of protective devices 433.1 — Coordination between conductor and overload protective devices

Except in two cases (431.1.2), detection of overcurrent is required for all line conductors and should cause disconnection of the conductor in which the overcurrent is detected.

Every circuit is to be designed so that a small overload of long duration is unlikely to occur.

Disconnection of other line conductors is not necessary, unless the loss of one phase could cause danger or damage (e.g. in a 3-phase motor)

When an overload occurs, the protective device should automatically disconnect the circuit (e.g. by tripping the MCB or rupturing / blowing a fuse).


Page | 88

17th Edition Training Manual Where no overload protection is provided, the temperature of the circuit conductors may rise excessively, possibly damaging the insulation, joints and terminations of the

Coordination will be met and comply with Regulation 433.1.1 if: Ib ≤ In ≤ Iz Where: IbIs the design current of circuit (i.e. the load) InIs the rated current or current setting of the protective device IzIs the current-carrying capacity of the conductor (i.e. a cable, busbar or powertrack) What this means is that the cable must have a current carrying capacity greater than that of the protective device, which must be able to manage the load required.


conductors and/or their surroundings. 433.1.1 — Coordination between conductor and overload protective device

Where the current (I2) causing effective operation of the protective device does not exceed 1.45 times the lowest of the current-carrying capacities(Iz) of any cable of the circuit, represented as: I2 ≤ 1.45 x Iz Which is:2 x In ≤ 1.45 x Iz In ≤ 1.45 / 2 x Iz ≤ 0.725 x Iz

433 — Rewireable fuses and buried cables

433.1.101 — Semi enclosed fuses (BS 3036), also comply if its rated current (In) does not exceed 0.725 times the currentcarrying capacity (Iz) of the lowest rated conductor in the circuit protected.

Page | 89

17th Edition Training Manual 433.1.102 — For buried cables and those buried in ducts etc, Regulation 433.1.4 requires a factor of 0.9 to be applied to the current-carrying capacity (Iz) of the lowest rated conductor in the circuit protected: In ≤ 0.9 Iz 433.2 — Position of devices for protection against overload Except where not required, a device for protection against overload is to be installed at the point where a reduction occurs in the value of current-carrying capacity of conductors:

433.3.1 — Omission of devices for protection against overload Where: •

A conductor is effectively protected against overload by a protective device placed on the supply side of that point

•

the characteristics of the load or the supply, is not likely to carry overload current (e.g. resistive load)

•

The Distributor agrees that their overload device(s) provide overload protection between the origin and the main distribution point of the installation

Fig. 30 Distributor's overload device

433.3.3 — Omission of devices for protection against overload for safety reasons To avoid unexpected disconnection of a circuit (causing danger or damage) the following, as examples, do not require overload protection: •

Exciter circuits of rotating machines

•

The supply circuit of lifting magnet

•

The secondary circuit of a current transformer

•

A circuit supplying a fire extinguisher device

•

A circuit supplying a safety service

434 — Protection against fault current

The prospective fault current at every relevant point of the


Page | 90

17th Edition Training Manual installation is to be determined. In a single-phase circuit, this would be the higher value of either line to earth, or line to neutral. In a three-phase circuit, this would be the highest value between all live conductors.The highest value measured is usually at the origin. Prospective fault current can be determined by calculation, measurement or enquiry. 434.2 — Position of devices for protection against fault current Like overload protection, a device providing protection against fault current is usually installed at the point where a reduction occurs in the cross-sectional area…… causing a reduction in the current-carrying capacity of conductors

have worked. This will be shown later on in the calculations section. Some installations, like the following, do not require protection against fault current: •

A conductor connecting a generator, transformer.

•

A circuit where disconnection could cause danger such as those quoted in omission of overload.

•

Certain measuring circuits.

•

The origin of an installation provided the distributor install one or more devices to provide affordable protection.

434.2.1 — Position of devices for protection against fault current Except where not required, no device for fault current protection is required provided the conductor: •

Does not exceed 3 m in length.

•

Is installed in such a manner as to reduce the risk of fault to a minimum.

•

Is installed in a manner to reduce to a minimum the risk of fire or danger to persons.

The reasoning behind this is that it is deemed that any cable above 4mm2has within 3m enough resistance to withstand 33kA at which point the previous protective device should


Page | 91

17th Edition Training Manual Calculation of maximum permissible fault clearance time:

TIs the duration of the fault, in seconds. S Is the conductor cross-sectional area in mm2. I Is the effective fault current, in amperes, expressed for A.C. as the rms value, due account being taken of the current limiting effect of the circuit impedances. K

Is a factor taking account of resistivity,

temperature coefficient and heat capacity of the Fig. 31 Protection device not required

Typical example of where a device for protection against fault current is not required. Conductors having a reduction in current-carrying capacity between the busbars and the switchboard


conductor material, and the initial and final conductor temperatures. For common materials, the values of k are in Table 43.1

Page | 92

17th Edition Training Manual Ch44 - Protection Against Voltage Disturbances & Electromagnetic Disturbances 442 — Protection of low voltage installations against temporary overvoltages due to earth faults in the high voltage system and due to faults in the low voltage system

The following four situations can have an effect on the safety of an LV installation by creating temporary overvoltages: •

A fault between the HV system and Earth in the transformer. (Regulation Group 442.2).

•

Loss of the supply neutral in the LV installation (Regulation 442.3).

•

Short-circuit between a line conductor and neutral in the LV installation (Regulation 442).

•

Accidental earthing of a line conductor of an LV IT system (Regulation 442.4).

443 — Protection against overvoltages of atmospheric origin or due to switching

As the UK has ≤ 25 thunderstorm days per year (AQ1). NO additional protection is required against overvoltages of atmospheric origin where installations are supplied by LV overhead lines. Refer to Table 44.4 for examples of various impulse categories of equipment.Switching overvoltages may be generated within an installation as the result of switching of: •

High current loads,


•

Inductive loads, such as motors, transformers or arc welding equipment, or

•

Capacitive loads, such as power factor correction equipment.

444 — Measures against electromagnetic influences added in AM1 Section 444 has been added in Amendment 1 of the IET Wiring Regulations to provide basic requirements and recommendations to enable the avoidance and reduction of electromagnetic disturbances.

Electromagnetic compatibility, better known as EMC, is the prerequisite for the correct design and functioning of electrical equipment in an installation to prevent electromagnetic radiation from some equipment does not influence the operation of other equipment within the installation or vicinity to operate. This section is important when designing an electrical installation as consideration will need to be taken into account to reduce electromagnetic disturbances on electrical equipment. IT equipment and equipment with electronic components or circuits can be particularly prone to damage or disturbances which can be caused by lightning, switching operations, short-circuits or other electromagnetic phenomena. These effects can be potentially more severe: •

where large metal loops exist

•

where different electrical wiring systems are

Page | 93

17th Edition Training Manual installed in common routes. e.g. data communication cables connecting IT equipment within a building. An important consideration is with regards to medical equipment which which can be affected by electromagnetic disturbances associated with electrical installations. 444.4.1 Sources of electromagnetic disturbances Consideration shall be given to the location of the sources of electromagnetic disturbances relative to the positioning of other equipment. Typical sources of electromagnetic disturbances: •

switching devices for inductive loads

•

electric motors

•

fluorescent lighting

•

welding machines

•

rectifiers

•

choppers

•

frequency convertors/regulators including Variable Speed Drives

•

lifts

•

transformers

•

switchgear

•

power distribution busbars

Further information can be found by referring to the BS EN 50174 standards series.


444.4.2 Measures to reduce EMI Regulation 444.4.2.1 identifies measures to be considered, where appropriate, in order to reduce the effects of electromagnetic interference. This covers screened signal or data cables, the use of surge protective devices, the installation of power cables, the separation of power and signal cables and the installation of an equipotential bonding network with reference to Regulation 444.5.3 444.4.3 TN system This deals with requirements to minimize electromagnetic disturbances in a TN system. 444.4.3.1 A PEN conductor shall not be used downstream of the original installation. Note that Regulation 8(4) of the Electricity Safety, Quality and Continuity Regulations 2002 prohibits the use of PEN conductors in consumers’ installations in the UK. 444.4.3.2 The installation shall have separate neutral and protective conductors downstream of the origin of the installation. 444.4.4 TT system Consideration shall be given to overvoltages which might exist between live parts and extraneous-conductive-parts where the extraneous-conductive-parts of different buildings are connected to different earth electrodes. The use of an isolating transformer to provide a TN-S system shall be considered.

Page | 94

17th Edition Training Manual 444.4.6 Multiple source TN or TT power supplies For TN or TT multiple source power supplies to an installation, the system shall be earthed at one point only. 444.4.7 Transfer of supply In an installation forming part of a TN system, the transfer of supply to an alternative supply shall be by means of a multipole switching device which switches the line conductors and the neutral conductor, if any. (This method prevents electromagnetic fields due to stray currents in the main supply system of an installation) Note the sections and regulations concerning separate buildings, inside buildings, within a single building and between buildings. Note that these refer to other regulations and British Standards. 444.5.2 Equipotential bonding networks The structure for bonding conductors shall be appropriate for the installation. 444.5.3 Sizing and installation of copper bonding ring network conductors Equipotential bonding designed as a bonding ring network shall have the following minimum nominal dimensions: •

Flat cross-section: 25 mm x 3 mm

•

Round diameter: 8 mm

Bare conductors shall be protected against corrosion at their supports and on their passage through walls. 444.5.3.1 Parts to be connected to the equipotential bonding network © 2008-2015 Electacourse

Note the parts required by the regulation to be connected to the equipotential bonding network: •

Metallic containment, conductive screens, conductive sheaths or armouring of data transmission cables or of IT equipment.

•

Functional earthing conductors of antenna systems

•

Conductors of the earthed pole of a d.c. supply for IT equipment.

•

Functional earthing conductors.

•

Protective conductors.

444.5.7.1 Earthing arrangements and equipotential bonding of IT installations for functional purposes 444.5.7.1 Earthing busbar Where an earthing busbar is required for functional purposes, consideration shall be given to extending the main earthing terminal of the building by using one or more earthing busbars. The purpose of this is to enable information technology (IT) installations to be connected to the main earthing terminal by the shortest practicable route from any point in the building. A new regulation governs the cross-sectional area of the busbar: 444.5.7.2 Cross-sectional area of the earthing busbar For installations connected to a supply having a capacity of 200 A per phase or more - minimum cross sectional area

Page | 95

17th Edition Training Manual 50mm2 copper and shall be selected in accordance with Regulation 444.5.2(iii) For supplies having a capacity of less than 200 A per phase, then the earthing busbar shall be selected in accordance with Table 54.8 which can be found on page 167 of BS7671:2008 Amendment 1. Where the earthing busbar is used as part of a d.c. return current path, its cross sectional area shall be selected according to the expected d.c. return currents. 444.6 Segregation of circuits Low voltage and extra low voltage cables sharing the same cable management system or route shall be installed according to Regulations 528.1 and 528.2

automatically or unexpectedly on the restoration of the power. In BS7671: 2008 there is a requirement that suitable precaution to be taken where this danger may occur. Regulation 445.1.1 refers to regulation 522.1.3, which states that every motor to be fitted with means to prevent automatic restarting after a stoppage due to a drop in voltage or failure of supply. Where unexpected restarting of the motor might cause danger, one way of addressing the problem is to install starters incorporating undervoltage relays with manual restart facilities.

444.6.2 Equipment Note that the minimum distance between IT cables and high intensity discharge lamps shall be 130 mm. Section 444 was ‘reserved for future use’ in the 17th Edition:2008 (red cover) publication. Section 444 has now been added to Amendment 1 (green cover) and no doubt questions on this new section will arise in the 2382 Requirements for Electrical Installations exam. Section 444 is not a large section, but it contains some important regulations and clear illustrations. It’s worth taking a little time to read through section 444 and familiarise yourself with its content at this point in the course.445 — Protection against undervoltage Where a reduction or a loss in voltage happens, there is a potential danger that any equipment may restart © 2008-2015 Electacourse

Page | 96

17th Edition Training Manual REVIEW QUESTIONS – Part 4 Protection for Safety

Question 1

Question 3

Which one is the most commonly used protective measure against electric shock?

A circuit protective conductor shall be run to and terminated at each point in wiring and at each accessory except

A.

Automatic disconnection of supply

A.

a connection point

B.

Double or reinforced insulation

B.

an earthing point

C.

a voltage source

D.

a lamp holder having no exposed-conductive-parts and suspended from such a point.

C. Electrical separation for the supply to one item of current-using equipment D.

Extra-low voltage (SELV and PELV)

Question 2 The provision for fault protection against electric shock may be omitted for A. Metal supports of overhead line insulators which are attached to the building and are placed out of arm's reach

Question 4 In each installation main protective bonding conductors shall connect to the main earthing terminal extraneousconductive-parts including: A.


B.

Switchers and connectors

B.

metal pieces of furniture

C.

Unearthed lines

C.

power supply

D.

Low voltage supply lines

D.

multimedia network system cables


Page | 97


Question 7

In case of a fault, the maximum disconnection time for a d.c. circuit with line voltage to Earth in the range 120 V-230 V in a TN system (for final circuits not exceeding 32 A) is A.

0.5 sec

Which type of circuit does BS7671 not refer to when considering the ommission of a device for protection against overload, eventhough unexpected disconnection may cause danger or damage

B.

0.2 sec

A.

a circuit supplying luminaires

C.

0.4 sec

B.

a circuit supplying a fire extinguishing device

D.

0.1 sec

C.

the exciter circuit of a rotating machine

D.

a circuit supplying a safety service, such as a fire alarm or a gas alarm

Question 6 Where disconnection of the neutral conductor in IT system is required, disconnection and reconnection shall be such that A.

the neutral conductor shall be disconnected before the line conductors and shall be reconnected at the same time as or before the line conductors.

B.

the neutral conductor shall not be disconnected before the line conductors and shall be reconnected at the same time as or before the line conductors.

C.

D.

the neutral conductor shall not be disconnected at the same time as or before the line conductors and shall be reconnected after the line conductors.

Question 8 For an installation with nominal voltage 400/690 V the required minimum impulse withstand voltage of category I overvoltage protective device (equipment with reduced impulse voltage) is A.

2.5 kV

B.

4 kV

C.

5 kV

D.

6 kV

the neutral conductor shall be disconnected before the line conductors and shall be reconnected at the same time as or after the line conductors.


Page | 98


Question 10

When tested at 5 times the rated operating current, an RCD used for additional protection should operate within

Under what circumstances is additional protection not required by means of an RCD in <20A circuit

A.

400ms

A.

when applied to mobile equipment outdoors

B.

40ms

B.

it is always required

C.

0.2s

C.

D.

0.5s

when in a dwelling a documented risk assessment determines RCD protection is not necessary

D.

it is never required in any circumstance

ANSWERS – Protection for safety 1A, Ref: BS7671: 410.3.3 2A, Ref: BS7671: 410.3.9 3D, Ref: BS7671: 411.3.1.1 4A, Ref: BS7671: 411.3.1.2 5A, Ref: BS7671: 411.3.2.2 6B, Ref: BS7671: 431.3 7A, Ref: BS7671: 433.3.3 8A, Ref: BS7671: 443.2.6 9B, Ref: BS7671: 415.1.1 10C, Ref: BS7671: 411.3.3


Page | 99


PART 5 — SELECTION & ERECTION OF EQUIPMENT

We’ll now work through Part 5. Many of the important regulations have been highlighted in this part and relevant regulations and definitions are expanded upon and illustrated where necessary. Chapter 51: Common rules (Compliance with Standards, external influences, identification (circuit and wiring systems) notices, etc. Chapter 52:Selection and erection of wiring systems (types of wiring system, mechanical protection including cables in walls etc.), requirements for the

monitoring. Chapter 54: Earthing arrangements and protective conductors (sizing of CPCs, earthing conductors and main bonding conductors). Chapter 55:Other equipment (generators, transformers etc and Section 559 Luminaires and lighting installations). Chapter 56:Safety services (Sources, circuits and wiring systems).

methods of support of wiring systems in escape routes. Chapter 53: Protection, isolation, switching control and


Page | 100

17th Edition Training Manual Part 5 deals with the selection of equipment and its erection. It provides some common rules for the compliance with the measures of protection for safety, and requirements for proper functioning of the intended use of the installation and any external influences that may affect that installation.

Ch 51 - Common Rules 511 — Compliance with Standards

Every item of equipment will comply with: •

The relevant requirements of an applicable current British Standard (BS) or Harmonized European standard, or

•

Any foreign national standard based on an IEC standard provided the designer or specifier of the installation verifies that any differences between these Standards will not result in a lesser degree of safety than the relevant British Standard.

512.1 — Operational conditions:

512.1.4 — Power 512.1.5 — Compatibility 512.1.6 — Voltage impulse 512.2 — External influences: Electrical equipment to be designed appropriate to the situation in which it is to be used or its mode of installation should take account of the conditions likely to be encountered. (Refer to Appendix 5 of BS 7671:2008 for more specific information.)

513 — Accessibility

Equipment, especially joints in cables, to be installed so that it can be easily operated, inspected and maintained and provide ease of access to any connections.

514 – Identification and notices

This section covers the requirements for a label or other suitable means of identification to avoid any possibility of confusion and to indicate the purpose of each item of switchgear:

Equipment to be suitable for its intended operational conditions.

•

Identification

•

Diagrams and

512.1.1 — Voltage

•

Warning notices including colour identification of

512.1.2 — Current

cables and wiring systems.

512.1.3 — Frequency


Page | 101

17th Edition Training Manual 514.3 — Identification of conductors Every core of a cable should be identified at its terminations and preferably throughout its length.Except where identification is not required, cores of cables should be identified by colour, letters or numbers. Table 51 of BS 7671 provides the details in relation to identification of conductors.

Fig. 32 Harmonized wiring colours


Page | 102

17th Edition Training Manual 514.8 — Identification of protective devices Circuit protective devices are required to be arranged and identified so that the circuit protected may be easily recognized.

A permanent label to BS951 with the words “Safety Electrical Connection — Do Not Remove” shall be permanently fixed in a visual position near: •

an earth electrode.

514.9 — Diagrams and documentation A legible diagram, chart or table (or equivalent form of information) must be provided indicating information on that particular installation, this is more detailed in BS7671:2008 [Amendment 1 - p 117]. For simple installations the information may be given in a schedule, a durable copy of which — relating to the distribution board — should be provided within or adjacent to each distribution board.

The connection between an earthing conductor and

•

The connection between every bonding conductor and an extraneous-conductive-part.

•

The main earth terminal.

514.14 — Warning notice: non-standard colours If alterations are made to an existing installation and there are two versions of wiring colours then a warning notice to indicate this must be displayed.

514.10 — Warning notice: voltage A warning notice is required where a voltage in excess of 230 V exists,and where this voltage would not normally be expected. This notice must be clearly visual before any access is gained to this dangerous live part. 514.11 — Warning notice: isolation A durable notice shall be fixed to indicate live parts that are not able to be isolated by a single device. 514.12.2 — RCD notice (label A notice shall be placed in a prominent position where a installation incorporates a RCD. 514.13 — Warning notices: earthing and bonding connections


Fig. 33 Old and new wiring warning notice

Page | 103

17th Edition Training Manual 514.15 — Warning notice: alternative supplies (previously dual supplies)

carrying capacity of a cable or flexible cord from Tables 4D1A to 4J4A.

Where an installation includes alternative or additional sources of supply, warning notices should be affixed at the following locations in the installation. •

At the origin

•

At the meter position (if remote from origin)

•

At the consumer unit

•

At all points of isolation of both sources of supplies

515 — Prevention of mutual detrimental influence Electrical equipment shall be selected and erected to prevent any harmful influences between the electrical installation and any non-electrical installation envisaged. The equipment shall also be selected and erected to prevent any electromagnetic influences that may occur.

Ch52 - Selection & Erection of Wiring Systems 521 — Types of wiring system

Table 4A2 of Appendix 4 states which installation methods are appropriate for commonly installed conductors and cables. 521.3 — Types of wiring system Examples of wiring systems are shown in Table 4A2. This table should be used first to find the ‘installation method’ and then the reference method relating to it. The reference method is required to determine the current-


Fig. 34 Complex wiring installation

Page | 104

17th Edition Training Manual 521.4 — Busbar trunking systems Commonly used in buildings in a variety of ways to distribute electricity. Must comply with the requirements of BS EN 60439-2 / BS EN 61534, also addressed in the Appendix. Such trunking is used for both distribution and final circuitry by means of interconnecting busbar trunking of different ratings. Advantage of this type of system of overhead busbar trunking •

Is to supply machinery, providing flexibility.

•

Available in a wide range of current ratings (up to several thousand amperes).

•

Designed to be installed in installations where there may be high fault levels.

Another variation of this type of system is the ‘Rising main’ busbar. This trunking system is often used to provide supplies in multi-story commercial or domestic properties, as its capability to distribute the supply to individual floors within buildings. 521.4 — Powertrack systemsare commonly used for underfloor distribution systems feeding socket-outlets or office furniture, or above ceilings to provide supplies and final connection points to luminaires. They generally have a maximum


rating of 63 A and must comply with requirements of BS EN 61534 series. 521.5 — Electromagnetic effects Electromagnetic effects from incorrectly installed cables of alternating current (a.c.) circuits can cause heat. To prevent such heat, which may damage cables and other materials, single-core cables armoured with steel wire or steel tape must not be used for a.c. circuits. 521.6 — Conduit, ducting, trunking and ladder systems Two or more circuits are allowed in the same conduit, ducting or trunking system provided the requirements of Section 528 are met. Regulations 521-6 to 521-10 provide some general requirements for these wiring systems including: •

Multiple circuits are permitted within the same wiring system or multi-core cable (See Section 528 though).

•

Separation of conductors from different final circuits (See also Section 314).

•

Use of flexible cables or cords (See also Section 522).

•

Non-sheathed cables of fixed wiring to be enclosed (See also Section 522).

521.10 — Installation of cables 521.10.1 Non-sheathed cables for fixed wiring shall be enclosed in conduit, ducting or trunking. This requirement

Page | 105

17th Edition Training Manual does not apply to a protective conductor complying with Section 543.

There is still an exception for cables forming part of a SELV or PELV circuit.

Non-sheathed cables are permitted if the cable trunking system provides at least the degree of protection IPXXD or IP4X, and if the cover can only be removed by means of a tool or a deliberate action.

521.11.201 Wiring systems in escape routes shall be supported such that they will not be liable to premature collapse in the event of fire. The requirements of Regulation 422.2.1 shall also apply, irrespective of the classification of the conditions for evacuation in an emergency.

NOTE : For a cable trunking system to meet IP4X requirements, IP4X trunking and related system components would need to be installed. If a system includes sitefabricated joints the installer must confirm the completed item meets at least the degree of protection IPXXD. 521.10.201 A bare live conductor shall be installed on insulators.

NOTE 1: Non-metallic cable trunking or other non-metallic means of support can fail when subject to either direct flame or hot products of combustion. This may lead to wiring systems hanging across access or egress routes such that they hinder evacuation and firefighting activities.

Wiring in escape routes

NOTE 2: This precludes the use of non-metallic cable clips, cable ties or cable trunking as the sole means of support. For example, where non-metallic cable trunking is used, a suitable fire-resistant means of support/retention must be provided to prevent cables falling out in the event of fire.

The regulations concerning selection and erection of wiring systems (impact) have been redrafted. Reference to “under the supervision of a skilled or instructed person” has been removed.

In 2012at Shirley Towers, Southampton, two members of the Hampshire Fire Brigade lost their lives. The investigation found that becoming entangled in cables fallen from the roof was a contributory factor in the deaths of Jim Shears and Alan Bannon.

A new Regulation (521.11.201) is included, giving requirements for the methods of support of wiring systems in escape routes.

It is now required to protect cables concealed in a wall or partition (at a depth of less than 50 mm) by a 30 mA RCD for all installations if other methods of protection including use of cables with an earthed metallic covering or mechanical protection are not employed. This applies to a cable in a partition where the construction includes metallic parts other than fixings, irrespective of the depth of the cable.


Investigation into a previous fire in Stevenage in 2005 came to a similar conclusion. Regulation 521.11.201 will help prevent significant loss of life and serious injury due to cables and non-metallic containment obstructing escape routes during fires due to the melting of fixings and accessories.

Page | 106

17th Edition Training Manual An external influence is defined as ‘Any influence external to an electrical installation which affects the design and safe operation of that installation.’

External influences to be considered.

Section 522 outlines the external influences, categorized in Appendix 5 and provides further information relating to electrical installations.

Fig. 35 Aftermath of fire at Shirley Towers in Southampton

522 — Selection & Erection of Wiring Systems in relation to External Influences

All electrical installations shall be selected so that it has the correct protection against any of the expected external influences. This will also be taken into consideration especially when it enters equipment.


522.1 — Ambient temperature (AA) Highest and lowest temperatures to be considered. When erecting systems and installing cables, the ambient temperature must also be considered. 522.2 — External heat sources Heat from an external source can be detrimental to wiring systems. Cables and flexible cords that are installed inside accessories, appliances or luminaires must be suitable for temperatures likely to be encountered or additional insulation, suitable for those temperatures, should be provided. Methods allowed:

Page | 107


Shielding

•

Placing sufficiently far from the heat source.

•

Selecting a system with due regard for the additional temperature rise that may occur.

•

Local reinforcement or substitution of insulation material.

522.3 — Presence of water (AD) or high humidity (AB) A wiring system shall be selected and erected so that no damage is caused by the ingress of water or condensation.

Fig. 36 We may not see sandstorms like this in the UK, but dust and particles can cause significant damage

522.5 — Presence of corrosive or polluting substance (AF) Where there is the presence of a corrosive or polluting substance, including where water is likely to cause corrosion or deterioration, the vulnerable parts of the system shall be suitably protected of manufactured from a material resistant to such substances. 522.4 — Presence of solid foreign bodies (AE) A wiring system shall be selected and erected so that no damage is caused by the ingress of solid foreign bodies.


Consideration must be taken where two dissimilar metals may cause electrolytic action.

Page | 108

17th Edition Training Manual An assessment must be made of the likely impact on wiring systems.Risk of impact is categorized as:

50 mm from a surface of the wall or partition shall: i)

low (AG1),

wall or partition or within 150 mm of an angle formed

medium (AG2), and

by two adjoining walls or partitions. Where the cable is

high severity (AG3)

connected to a point, accessory or switchgear on any surface of the wall or partition, the cable may be

522.6 — Impact (AG Wiring systems are required to be protected from damage arising from mechanical stress.The following need to be considered during installation, use or maintenance:

installed in a zone either horizontally or vertically, to the point, accessory or switchgear. Where the location of the accessory, point or switchgear can be determined

•

Impact

from the reverse side, a zone formed on one side of a

•

abrasion

wall of 100 mm thickness or less or partition of 100 mm

•

penetration

thickness or less extends to the reverse side, or

•

tension or compression

522.6.201 A cable installed under a floor or above a ceiling shall be run in such a position that it is not liable to be damaged by contact with the floor or ceiling or their fixings. A cable passing through a joist within a floor or ceiling construction or through a ceiling support (e.g. under floorboards), shall: i)

be installed in a zone within 150 mm from the top of the

be installed at least 50 mm measured vertically from the top, or bottom as appropriate, of the joist or batten, or

ii) comply with Regulation 522.6.204. 522.6.202 A cable installed in a wall or partition at a depth of less than


ii) comply with Regulation 522.6.204. Where indent (i) but not indent (ii) applies, the cable shall be provided with additional protection by means of an RCD having the characteristics specified in Regulation 415.1.1. 522.6.203 Irrespective of its buried depth, a cable concealed in a wall or partition, the internal construction of which includes metallic parts, other than metallic fixings such as nails, screws and the like, shall: i)

be provided with additional protection by means of an RCD having the characteristics specified in Regulation 415.1.1, or

ii) comply with Regulation 522.6.204.

Page | 109

17th Edition Training Manual For a cable installed at a depth of less than 50 mm from the surface of a wall or partition the requirements of Regulation 522.6.202 shall also apply. 522.6.204 For the purposes of Regulation 522.6.201(ii), Regulation 522.6.202(ii) and Regulation 522.6.203(ii), a cable shall: i)

incorporate an earthed metallic covering which complies with the requirements of these Regulations for a protective conductor of the circuit concerned, the cable complying with BS 5467, BS 6724, BS 7846, BS

particularly where cables and cable connections are concerned. 522.8 — Other mechanical stresses (AJ) A wiring system should be selected and erected to avoid during installation, use or maintenance, damage to the sheath or insulation of cables and their terminations. The radius of every bend in a wiring system should be such that no damage occurs and terminals are not stressed. Cables need to be supported continuously so as not to suffer damage or strain from their own weight.

8436 or BS EN 60702-1, or ii) be installed in earthed conduit complying with BS EN 61386-21 and satisfying the requirements of these Regulations for a protective conductor, or iii) be enclosed in earthed trunking or ducting complying with BS EN 50085-2-1 and satisfying the requirements of these Regulations for a protective conductor, or iv) be provided with mechanical protection against damage sufficient to prevent penetration of the cable by nails, screws and the like, or v) form part of a SELV or PELV circuit meeting the requirements of Regulation 414.4. 522.7 — Vibration (AH) A wiring system supported by or fixed to a structure or equipment subject to vibration of either medium (AH2) or high severity (AH3) must be suitable for such conditions,


Fig. 37 Wiring supported by cable tray (in this example this is likely to be network cabling and not an electrical installation)

Except where installed within a conduit or duct that provides adequate mechanical protection, cables buried in the ground must incorporate an earthed amour or metal sheath or both, suitable for use as a protective conductor. The location of buried cables should be marked by cable

Page | 110

17th Edition Training Manual covers or suitable marking tape, and should be buried at a sufficient depth to avoid damage. 522.8.14 — Penetration of an element of building construction Wiring systems should not penetrate an element of building construction intended to be load bearing unless the integrity of the load-bearing element can be assured after such penetration. The other regulations in 522.x cover Presence of Flora and /or mould growth (AK), Presence of Fauna (AL), Solar and Ultraviolet radiation (AN), Seismic effects (AP), Movement of air (AS) (previously ‘wind’), Nature of processed or stored materials (BE), Building design (CB) The above regulations are defined more in Appendix 5.

523 — Current-Carrying Capacities of Cables

The requirement of this regulation is considered satisfied if the current for non-sheathed and sheathed cables does not exceed the appropriate values selected from the tables of current carrying capacity given in Appendix 4 523.5 — Groups containing more than one circuit For groups of cables there is a grouping factor which can be found in Tables 4C1 to 4C6 of Appendix 4. 523.8 — Variation of Installation conditions along a route Where the heat differs in one part of a route to another, the current-carrying capacity shall be appropriate for that part of the route having the most adverse conditions.

523.9 — Cables in Thermal Insulation A cable should preferably not be installed in a location where it is liable to be covered by thermal insulation. Where a cable is to be run in a space to which thermal insulation is likely to be applied, the cable shall wherever practicable be fixed in a position such that it will not be covered by the thermal insulation. Where fixing in such a position is impractical the cross-sectional area of the cable shall be selected to meet the requirements of Chapter 43. For a cable installed in a thermally insulated wall or above a thermally insulated ceiling, the cable being in contact with a thermally conductive surface on one side, current-carrying capacities are tabulated in Appendix 4. For a single cable likely to be totally surrounded by thermally insulating material over a length of more than 0.5 m, the current-carrying capacity shall be taken, in the absence of more precise information, as 0.5 times the current-carrying capacity for that cable clipped direct to a surface and open (Reference Method C). Table 52.2 Cable surrounded by thermal insulation Length in insulation (mm)

Derating factor

50

0.88

100

0.78

200

0.63

400

0.51

Table 11 Derating factors for insulated cable - Table 52.2 of BS7671


Page | 111

17th Edition Training Manual 524.1 — Cross-sectional areas of conductors of cables The cross-sectional area of each conductor in an A.C. circuit or of a conductor in a D.C. circuit shall be not less than the value given in Table 52.3. For information about minimum csa of conductors for extralow voltage lighting installations, see Regulation 559.11.5.2. 524.2 — Cross-sectional area of neutral conductor A neutral conductor is required to have a cross-sectional area not less than that of the line conductor: • •

in single-phase, two-wire circuits whatever the

protection. The following dangers need to be protected against: •

fire or other harmful thermal effects

•

contact with a live part

•

failure of fault protection measures

526.3 — Accessibility of connections With certain exemptions, electrical connections (including protective conductors) should be accessible for the purposes of:

cross-sectional area.

•

inspection

in polyphase and single-phase three-wire circuits,

•

testing

where the size of the line conductors is less than or

•

maintenance

equal to 16 mm2 for copper, or 25 mm2 for aluminum.

525 — Voltage drop in consumers’ installations

The regulations are deemed to be satisfied if the voltage drop between the origin of the installation (usually the supply terminals) and that of the socket-outlet or the terminals of fixed current-using equipment does not exceed that stated in Appendix 4, Section 6.4. That is 3% for lighting and 5% for other uses from the public electricity supply and 6% and 8% respectively for private electricity supply

526 — Electrical connections

Every connection between conductors or between a conductor and other equipment should provide durable electrical continuity and adequate mechanical strength and


Connections in non-readily accessible locations. Connections made in roof spaces, inter-floor spaces and other non-readily accessible locations should be enclosed, and ‘normally’ fixed. Effects of temperature of connections on insulation. The temperature attained by a connection should not impair the effectiveness of the insulation of the conductors connected to it or any insulating material used to support the connection. A cable that utilizes thermosetting insulation(often called XLPE), has a maximum operating temp for insulation of 90°C.

Page | 112

17th Edition Training Manual 526.5 — Requirements for terminations and joints to be enclosed in: •

A suitable accessory (such as a lighting switch or a socket-outlet).

•

An equipment enclosure (see opposite).

•

An enclosure partially formed or completed with building material, which is non-combustible when tested to BS 476-4.

526.9 — Requirements for sheathed and non-sheathed cable enclosure Cores of sheathed cables from which the sheath has been removed and non-sheathed cables at the termination of conduit etc. should be enclosed.(as required by Regulation 526.5)

527 — Selection and erection of wiring systems to minimize the spread of fire

Section 527 considers two aspects in relation to the risk of spread of fire: •

The precautions within a fire-segregated compartment (527.1) and

•

The sealing of wiring system penetrations (527.2)

The risk of spread of fire should be minimized by the selection of appropriate materials and erection methods. Wiring systems shall be installed so that the general building structural performance and fire safety are not reduced. Cables: Most common cables will comply, without further


precautions, provided they comply with, at least, BS EN 60332-1-2 (which relates to fire tests on cables). Conduit and trunking systems: Should comply with their product standard in which case no further precautions are required.Where a conduit or trunking system passes through elements of building construction, the opening remaining after the passage of the wiring system is required to be sealed according to the degree of fire resistance of the building element prior to penetration. 527.2.3 — Internal sealing of wiring systems Review Regulation 527.2.6 for the requirements relating to the sealing of conduit, trunking or ducting. Internal sealing of wiring systems such as conduit, trunking or ducting is not required where the system is classified as non- flame propagating according to the relevant product standard and has a maximum internal cross-sectional area of 710 mm2 provided that: •

The system provides a degree of protection ≥ IP33, and

•

Any termination of the system in one of the compartments, separated by the building construction being penetrated, provides a degree of protection to IP33.

528 — Proximity of wiring systems to other services,

Section 528 sets out requirements for measures to be taken where electrical equipment, including wiring systems, are in close proximity to other electrical services and to non-

Page | 113

17th Edition Training Manual electrical services. Voltage bands I and II are used in Section 528 for the purposes of defining segregation. Neither a Band I or Band II circuit should be contained in the same wiring system as a circuit of nominal voltage exceeding that of low voltage, and Band I circuits should not be contained in the same wiring system as Band II circuits unless one (or more) of the following methods is adopted: 528.1 (i) — every cable or conductor is insulated for the highest voltage present (i.e. for the highest circuit voltage in excess of low voltage).

of 100 mm is to be maintained between services, or the requirements of Regulation 528.1 (i) or (ii) must be fulfilled. Wiring systems should not be installed in the vicinity of a service, which produces heat, smoke or fumes likely to be detrimental to the wiring, unless the wiring is protected against such harmful effects. Where condensation may occur, precautions have to be taken to prevent deleterious effects. 528.3.5 — Lift shafts The only cables that may be run in the lift or hoist shaft are those that form part of the lift installation as defined.

528.1 (ii) — each core of a multi-core cable is insulated for the highest voltage present in the cable. 528.1 (iii) — the cables are insulated for their system voltage and installed in a separate compartment. 528.1 (iv) — the cables are installed on a cable tray system where physical separation is provided by a partition. 528.1 (v) — a separate conduit, trunking or ducting system is employed. 528.1 (vi) — for a multi-core cable or cord, the cores of the Band I circuit are separated from the cores of Band II circuit by an earthed metallic screen. Proximity of communications cables (underground). Where underground power cables and telecommunications cables cross or are in close proximity a minimum clearance


Page | 114

17th Edition Training Manual 529 — Selection and erection of wiring systems in relation to maintainability, including cleaning

All electrical installations and electrical equipment will deteriorate over time due to accidental or deliberate damage, corrosion, electrical overloading and from environmental factors. Electrical installations may need to be maintained without undue difficulty and kept in a safe condition throughout its life in BS EN 81-1 series.

Ch53 - Protection, Isolation, Switching Control and Monitoring Section 530 deals with the common requirements for protection, isolation, switching control and monitoring. And in section 530.4 references the fixing of equipment, most generally according to manufacturer’s instructions.

531 — Fault protection by automatic disconnection of supply Reference is made to Chapter 41 and the nature of the supply system: TN, TT or IT which detail the selection and erection of devices for fault protection. 531.2 RCD Devices Summary of RCD requirements: An RCD should be capable of disconnecting all line conductors at substantially the same time. An RCD cannot be used for fault protection on its own, for example where a circuit does not contain a protective conductor.

Fig. 38 Installation design needs to take account of maintenance

Requirements for future maintenance should be assessed in the early stages of the electrical installation design and taken into account in the design.


Fig. 39 RCD device

Discrimination between devices is achieved the device electrically nearest

Page | 115

17th Edition Training Manual to the fault operates, leaving other upstream protective device(s) still supplying other circuits. Review Sections 531.3, 531.4, 531.5 to understand the regulations relating to RCDs in alternative supply systems.

532 — Devices for protection against the risk of fire Where it is necessary to limit the consequence of fault currents with respect to the risk of fire, an RCD should be installed which: •

Complies with Regulation Group 531.2 for fault protection and

•

Is installed at the origin of the circuit to be protected and

•

Switches all live conductors, and

•

Has a rated residual operating current ≤300 mA.

536 — Coordination of protective devices

Where coordination of series protective devices is necessary to prevent danger and where required for proper functioning of the installation, consideration should be given to selectivity and/or any necessary back-up protection. Where selectivity between overcurrent devices or RCDs is necessary to prevent danger and where required for proper functioning of the installation, the manufacturers’ instructions must be taken into account.

537 — Isolation and switching

The term ‘isolation and switching’, relates to four distinct operating functions which are defined in Part 2 of BS 7671: •

Isolation (537.2)

•

Switching off for mechanical maintenance (537.3)

•

Emergency switching (537.4)

•

Functional switching (537.5

533 — Devices for protection against overcurrent

Firefighter switches (537.6) are also covered in this section.

The relevant symbols are defined as:

Table 53.4 of BS 7671 provides guidance on the selection of protective, isolation and switching devices.

This section provides further information relating to the selection of devices for overload and fault current (to be read in conjunction with Chapter 43) Ib - The current for which the circuit is designed i.e. the current intended to be carried in normal service. Iz - The current-carrying capacity of the cable. In - The rated current of the protective device. I2 - The current giving effective operation of the overload protective device.


General requirements

Each installation is to have provision for disconnecting supply. A main linked switch or linked circuit breaker is required as near as practicable to the origin of every installation as a means of switching the supply on load and as a means of isolation. Where an installation is supplied from more than one source, a main switch is required for each source of supply

Page | 116

17th Edition Training Manual or alternatively, a suitable interlock system must be provided. Table 53.4 Guidance to the selection of protective, isolation and switching devices. This table has been introduced to clarify the application and function that the selected device is deemed to carry-out.This table also has the listed BS numbers of the selected device.

Table 53.4 – Guidance on the selection of protective, isolation and switching devices Device

Standard

Isolation

Emergency switching

Functional switching

Circuitbreaker

BS EN 608998

Yes

Yes

Yes

Yes

Yes

Yes

BS EN 60947-2

Yes

Yes

Yes

BS EN 60947-2

Yes

Yes

Yes

Yes

Yes

Yes

BS EN 61008-1

Yes

Yes

Yes

(5) Circuit-breakers and RCDs are primarily circuitprotective devices and, as such, they are not intended for frequent load switching. Infrequent switching of circuitbreakers on-load is admissible for the purposes of isolation or emergency switching. For a more frequent duty, the number of operations and load characteristics according to the manufacturer’s instructions should be taken into account or an alternative device from those listed as suitable for functional switching in Table 53.4 should be employed. 537.1.4 — General requirements A main switch intended for operation by ordinary persons e.g. of a household or similar installation, should interrupt both live conductors of a single-phase supply.

BS EN 61009-1 RCD

BS EN 61009-1 Table 12 Selection of protective, isolation and switching devices

Note added


Page | 117


Fig. 41 A locked RCD with notice Fig. 40 A consumer unit with a clearly identified main switch. From January 2016, such units will be constructed of material according to regulation 421.1.201

537.2 — Isolation Isolation is the function that allows operatives to work safely on electrical equipment, and is defined as:

Items to be considered in relation to isolation devices include: •

Numbers of poles to be isolated.

•

Isolation of groups and inconvenience.

•

Devices designed and/or installed to prevent unintentional or inadvertent closure.

‘A function intended to cut off for reasons of safety the supply from all, or a discrete section, of the installation by separating the installation or section from every source of electrical energy.’


•

Isolation devices to be clearly identified and indicate the installation or circuit it isolates.

Where an isolating device is placed remote from the equipment to be isolated, provision must be made to secure the device in the open position.

Page | 118

17th Edition Training Manual Where there is more than one source of supply a durable warning notice is required. 537.3 — Switching off for mechanical maintenance Switching off for mechanical maintenance is not necessarily intended to provide protection against electric shock. Switching off for mechanical maintenance is to enable nonelectrical maintenance to be performed safely without the risk of burns or injury from mechanical movement. Mechanical maintenance is defined as: •

•

‘The replacement, refurbishment or cleaning of

removal of the hazard by cutting off the appropriate supply. 537.5 — Functional switching Functional switching is provided for the users of electrical installations for normal operating purposes to control items of current-using electrical equipment. The equipment may be controlled either individually or in groups and via a manual or automatic operation.

and machinery.’

‘An operation intended to switch ‘on’ or ‘off’ or vary the supply of electrical energy to all or part of an installation for normal operating purposes.Examples of functional switching devices include:

Switching off for mechanical maintenance.

Emergency switching is defined as: ‘An operation intended to remove, as quickly as possible, danger, which may have occurred unexpectedly.’ The means for emergency switching must consist of either: •

operated by a single action and resulting in the

Functional switching is defined as:

Where, in case of danger, there is necessity for immediate interruption of supply, an interrupting device must be installed in such a way that it can be easily recognized and effectively and rapidly operated.

•

A combination of several items of equipment

lamps and non-electrical parts of equipment, plant

537.4 — Emergency Switching

•

•

A single switching device directly cutting off the

•

A switch in a socket-outlet

•

A contactor switching the supply

•

Push buttons

•

A thermostat

•

A pressure switch

•

A micro switch

537.6 — Firefighter switches A firefighter switch shall be provided in a low voltage system supplying exterior electrical installations and interior discharge lighting installations operating at a voltage exceeding low voltage.

incoming supply, or


Page | 119

17th Edition Training Manual Fig. 42 Sign indicating presence of a fireman's switch

527.6.3 — Every firefighters switch will comply with the following requirements and in conjunction with the local fire authority For an exterior installation, the switch shall be outside the building and adjacent to the equipment, or a notice indicating the position of the switch must be placed next to the equipment and a notice at the switch to indicate its control. In an interior installation, the switch will be located at the main entrance of the building. The switch will be: •

A conspicuous position

•

Accessible to firefighters

•

Not more than 2.75m from the ground

Where more than one switch is installed, each will be clearly marked to indicate the installation which it controls.

Fig. 43 Fireman's switch including extraction control

527.6.4 — Afirefighters switch will be: •

Coloured red and have fixed onto it or placed near it a permanent durable nameplate marked with the words ‘Firefighter’s Switch’. The minimum size of the plate to be 150mm x 100mm and the words legible from a distance but no less than 36 point.

•

It ON and OFF positions clearly marked by lettering and its OFF position at the top.

•

Have a device to prevent it being inadvertently returned to the ON position.

•

Be arranged so that it operation is easily facilitated by a firefighter.


538 — Monitoring

Page | 120

17th Edition Training Manual Section 538 of BS 7671 provides the requirements relating to monitoring. Within Section 538 there are two types of monitoring devices: aninsulation monitoring devices (IMD) (538.1), and Residual current monitor (RCM) (538.4) The IMD is part of an IT system and provides continuous monitoring of insulation resistance throughout the system. An IMD may or may not be connected to insulation fault location equipment.

538.4— Residual current (RCM) monitor An RCM permanently monitors any leakage current in the downstream installation or part of it; such a device is NOT intended to provide protection against electric shock. In supply systems, RCMs may be installed to reduce the risk of operation of the protective device in the event of excessive leakage current of the installation or the connected appliances. Where an RCD is installed upstream of the RCM, it is recommended that the RCM has a rated residual operating current not exceeding a third of that of the RCD.

Fig. 44 RCM Monitor


Page | 121


Ch54 - Earthing Arrangements & Protective Conductors Chapter 54 is concerned with the sizing of CPCs, earthing conductors and main bonding conductors. This is a common source of 2382-15 questions. 541.1 — Every means of earthing and every protective conductor shall be selected and erected so as to satisfy the requirements of the Regulations. 541.2 — The earthing system of the installation may be subdivided, in which case each part thus divided shall comply with the requirements of this Chapter. 541.3 — Where there is also a lightning protection system, reference shall be made to BS EN 62305.

542 — Earthing arrangements

542.1.100 — Main earthing terminal (MET) The main earthing terminal (MET) shall be connected with Earth by one of the methods described in Regulations 542.1.2 to 542.1.3, as appropriate to the type of system of which the installation is part.


Fig. 45 Main earthing terminal

Page | 122

17th Edition Training Manual Earthing arrangements explained It would be advantageous to recap on the different earthing supplies that are used, as previously described in Part 2 Definitions. Of the five mentioned the most commonly installed are TN-S, TNC-S and TT. TheSUPPLY system earthing arrangement is indicated by the first letter: T signifies that one or more points directly connected to Earth (‘T’ stands for ‘terre’, the French for Earthed.) The INSTALLATION earthing arrangements are indicated by the second letter: T Indicates that the exposed-conductive-parts of the installation are directly connected to Earth. N Indicates that the exposed-conductive-parts of the installation are directly connected to the earthed point of the source ofenergy. (‘N’ represents‘neutre’ neutral) The SYSTEM PROTECTIVE AND NEUTRAL CONDUCTOR arrangements are indicated by the following letters: S.Separate neutral and protective conductors are provided. (‘S’ is for‘separee’-separate). C Implies that the Neutral and protective functions are both performed by a single conductor, called a combined protective and neutral (PEN) conductor. (‘C’ stands for ‘commune’ combined)


Page | 123

17th Edition Training Manual 542.1.2.1 — TN-S

Fig. 46For a TN-S system, means shall be provided for the main earthing terminal of the installation to be connected to the earthed point of the source of energy.( Part of the connection may be formed by the distributor’s lines and equipment).


Page | 124

17th Edition Training Manual 542.1.2.2 — TN-C-S

Fig. 47For a TN-C-S system, where protective multiple earthing is provided, means shall be provided for the main earthing terminal of the installation to be connected by the distributor to the neutral of the source of energy


Page | 125

17th Edition Training Manual 542.1.2.3 — TT and IT

Fig. 48For a TT or IT system, the main earthing terminal shall be connected via an earthing conductor to an earth electrode complying with Regulation 542.2.


Page | 126

17th Edition Training Manual 542.1.2.4 — Where the supply to an installation is at high voltage, protection against faults between the high voltage supply and earth shall be provided in accordance with Section 442. 542.1.3.1 — The earthing arrangements shall be such that: 1. The value of impedance from the consumer’s main earthing terminal to the earthed point of the supply for TN systems, or to Earth for TT and IT systems, is in accordance with the protective and functional requirements of the installation, and considered to be continuously effective, and 2. Earth fault currents and protective conductor currents which may occur are carried without danger, particularly from thermal, thermomechanical and electromechanical stresses, and 3. They are adequately robust or have additional mechanical protection appropriate to the assessed conditions of external influence. 542.1.3.2 — Precautions shall be taken against the risk of damage to other metallic parts through electrolysis. 542.1.3.3 — Where a number of installations have separate earthing arrangements, any protective conductors common to any of these installations shall either be capable of carrying the maximum fault current likely to flow through them or be earthed within one installation only and insulated from the earthing arrangements of any other installation. In the latter circumstances, if the protective conductor forms part of a cable, the protective conductor


shall be earthed only in the installation containing the associated protective device. 542.2 — Earth electrodes 542.2.1 — The design used, and the construction of, an earth electrode shall be such as to withstand damage and to take account of possible increase in resistance due to corrosion 542.2.3 — Seven distinct types of earth electrode have been recognized in BS 7671.The following types of earth electrode are recognized for the purposes of the Regulations: 1. 2. 3. 4.

Earth rods or pipes. Earth tapes or wires. Earth plates. Underground structural metalwork embedded in foundations. 5. Welded metal reinforcement of concrete (except prestressed concrete) embedded in the earth. 6. Lead sheaths and other metal coverings of cables, where not precluded by Regulation 542.2.5. 7. Other suitable underground metalwork. (You can also refer to BS 7430 for further specifications) Earth rods and pipes Although suitable for many, if not most, earthing applications, solid rod orpipe earth electrodes are not particularly well suited to situationswhere rock or other hard layer prevent deep driving. Earth plates Earth plates are usually of copper or cast iron, and

Page | 127

17th Edition Training Manual normallynot more than 1.2 meters square. They are designed to belaid into the ground vertically and not horizontally (flat) asin many cases are.If the ground composition prevent this then Earth gridsand Earth tape as shown should be used. 542.2.4 — The type and embedded depth of an earth electrode shall be such that soil drying and freezing will not increase its resistance above the required value. 542.2.5 — The use, as an earth electrode, of the lead sheath or other metal covering of a cable shall be subject to all of the following conditions: •

Adequate precautions to prevent excessive deterioration by corrosion

•

The sheath or covering shall be in effective contact with earth

•

The consent of the owner of the cable shall be obtained

•

Arrangements shall exist for the owner of the electrical installation to be warned of any proposed change to the cable, which might affect its suitability as an earth electrode.

542.2.6 — A metallic pipe for gases or flammable liquids shall not be used for an earth electrode. The metallic pipe of a water utilityshall not be used for an earth electrode. Other metallic water supply pipework shall not be used unless precautions are taken to prevent its removal.

Four common earthing methods 1. 2. 3. 4.


Structural metalwork Earth plate Earth tape Earth rod

Page | 128

17th Edition Training Manual 542.3 — Earthing conductor The earthing conductor of an electrical installation is the protective conductor connecting the Main Earthing Terminal (MET) of the installation with the means of earthing (the external earthing system). Mechanical Damage

Protected

NOT protected

2.5mm2 copper

2.5mm2 copper

10mm2 steel

16mm2 steel

Corrosion Damage Protected by a sheath

NOT protected

Note:The covering of a green-and-yellow single-core cable is not a sheath. 542.4 — Main earthing terminals or bars (MET) MET connecting the earthing conductor to installation protective conductors. To facilitate measurement of the resistance of the earthing arrangement, a means of disconnecting the installation earthing conductor will be required. This provision may be combined with the main earthing terminal.

2.5mm2 copper 50mm2 steel

Table 13 Minimum cross-sectional area of a buried earthing conductor. BS7671 Table 54.1

Fig. 50 Disconnect by removing bolted link

Fig. 49 Earthing conductor


Page | 129

17th Edition Training Manual 543 — Protective conductors

Regulation Group 543 provides information on the selection of both type and cross-sectional area of protective conductors.Protective conductors are conductors provided for the purposes of safety. For example protection against electric shock.

Selected (in accordance with Regulation 543.1.4) or

•

Calculated (in accordance with Regulation 543.1.3)

Except where a protective conductor is an integral part of a cable, formed by a conduit, ducting or trunking or contained in an enclosure of a wiring system what is the minimum csa for a copper protective conductor if:

There are two methods that may be employed when choosing a protective conductor as required by Regulation 543.1.1. The cross sectional area (csa) of every protective conductor (other than protective bonding conductors, which are discussed later) must either be:

Cross-sectional area of a line conductor (mm2)

•

•

Protection against mechanical damage is provided, and

•

Mechanical protection is not provided.

Selection of protective conductor (reference to the related line conductor and Table 54.7

Minimum cross-sectional area of the corresponding protective conductor Protective conductor same material as line conductor (mm2)

NOT the same material (mm2)

S <16

S

16 < S < 35

16

𝑘1 ×𝑆 𝑘2

S > 35

𝑆 2

Table 14Cross-sectional areas of protective conductors.


𝑘1 × 16 𝑘2 𝑘1 𝑆 × 𝑘2 2

Page | 130

17th Edition Training Manual Calculation of protective conductors (adiabatic equation):

√𝐼 2 𝑡 𝑆= 𝑘

Where the “selection” method has not been utilized, every protective conductor, other than a protective bonding conductor, will need to be verified by use of the calculation method.

543.2.2 — Where a metal enclosure or frame of a low voltage switchgear or controlgear assembly or busbar trunking system is used as a protective conductor, it shall satisfy the following three requirements: •

construction or by suitable connection, in such a way as to be protected against mechanical, chemical or electrochemical deterioration. •

543.2.1 — A protective conductor may consist of one or more of the following: •

A single-core cable

•

A conductor in a cable

•

An insulated or bare conductor in a common enclosure with insulated live conductors

•

A fixed bare or insulated conductor

•

A metal covering, for example, the sheath, screen or armouring of a cable

•

A metal conduit or other enclosure or electrically continuous support system for conductors

•

An extraneous-conductive-part complying with Regulation 543.2.6.


Its cross sectional area shall be at least equal to that resulting from the application of Regulation 543.1,

543.2 — Types of protective conductor A gas pipe an oil pipe, Flexible or pliable conduit, support wires or flexible metallic parts or parts of a construction shall not be selected as a protective conductor.

Its electrical continuity shall be assured, either by

or verified by test in accordance with BS EN 604391. •

It shall permit the connection of other protective conductors at every predetermined tap-off point.

543.2.4 — A protective conductor of the types and of crosssectional area 10mm2 or less shall be copper 543.2.5 — The metal covering including the sheath (bare or insulated) of a cable, in particular the sheath of a mineral insulated cable, trunking and ducting for electrical purposes and metal conduit, may be used as a protective conductor for the associated circuit, if it satisfies both requirements of items (i) and (ii) of Regulation 543.2.2. 543.2.6 — Except as prohibited in Regulation 543.2.3, an extraneous-conductive-part may be used as a protective conductor if it satisfies all the following requirements: •

Electrical continuity shall be assured, either by construction or by suitable connection, in such a Page | 131

17th Edition Training Manual way as to be protected against mechanical, chemical or electrochemical deterioration. •

The cross-sectional area shall be at least equal to that resulting from the application of Regulation 543.1.1.

•

And unless compensatory measures are provided, precautions shall be taken against its removal.

•

And it has been considered for such a use and, if necessary, suitably adapted.

543.2.7 — Earthing tail requirement Where the protective conductor is formed by conduit, trunking, ducting or the metal sheath and/or armour of a cable, the earthing terminal of each accessory shall be connected by a separate protective conductor to an earthing terminal incorporated in the associated box or other enclosure.

formed by a metal covering or enclosure containing all of the conductors of the ring, the circuit protective conductor of every ring final circuit shall also be run in the form of a ring having both ends connected to the earthing terminal at the origin of the circuit. 543.2.10 — A separate metal enclosure for cable shall not be used as a PEN conductor. 543.3 — Preservation of electrical continuity of protective conductors 543.3.1 — A protective conductor shall be suitably protected against both mechanical and chemical deterioration and electrodynamic effects 543.3.2 — A protective conductor having a cross-sectional area up to and including 6 mm2 shall be protected throughout by a covering at least equivalent to that provided by the insulation of a single-core non-sheathed cable of appropriate size having a voltage rating of at least 450/750 V: •

A protective conductor forming part of a multicore cable.

•

Cable trunking or conduit used as a protective conductor.

543.3.5 — An exposed-conductive-part of equipment shall not be used to form a protective conductor for other equipment except as provided by Regulations 543.2.1, 543.2.2 and 543.2.5 543.2.9 — Except where the circuit protective conductor is


Where the sheath of a cable incorporating an uninsulated protective conductor of cross-sectional area up to and including 6 mm2 is removed adjacent to joints and terminations, the protective conductor shall be protected by insulating sleeving complying with BSEN 60684

Page | 132

17th Edition Training Manual 543.3.2 —Every connection and joint shall be accessible for inspection, testing and maintenance 543.3.3 — No switching device shall be inserted in a protective conductor except for the following: •

As permitted by Regulation 537.1.5.

•

Multipole linked switching or plug-in devices in which the protective conductor circuit shall not be interrupted before the live conductors and shall be re-established not later than when the live conductors are e-connected.

Joints, which can be disconnected for test purposes, are permitted in a protective conductor circuit. 543.3.4 — Where electrical earth monitoring is used, no dedicated devices will be connected in series with the protective conductor (see BS 4444). 543.3.6 — Every joint in metallic conduit shall be mechanically and electrically continuous 543.5.1 — Where earthing for combined protective and functional purposes is required, the requirements for protective measures shall take precedence.When energized and in normal use, some electrical equipment can cause current to flow in the circuit protective conductors.Equipment having such currents may include: Information technology equipment Industrial and telecommunications equipment with radiofrequency interference suppression filtering


•

High frequency luminaires, and

•

Certain types of heating elements

543.6 — Earthing Arrangements for Protective Purposes 543.6.1 — When overcurrent protective devices are used for protection against electric shock, the protective conductor shall be incorporated in the same wiring system as the live conductors or in their immediate proximity. 543.7 — Earthing requirements for the installation of equipment having high protective conductor currents 543.7.1.101 - Equipment having a protective conductor current exceeding 3.5 mA but not exceeding 10 mA, shall be either permanently connected to the fixed wiring of the installation without the use of a plug and socket-outlet or connected by means of a plug and socket complying with BS EN 60309-2. 543.7.1.102 — Equipment having a protective conductor current exceeding 10 mA shall be connected to the supply by one of the following methods: 1) Preferably by being permanently connected to the wiring of the installation, with the protective conductor elected in accordance with Regulation 543.7.1.103. The permanent connection to the wiring may be by means of a flexible cable. 2) A flexible cable with a plug and socket-outlet complying with BS EN 60309-2, provided that either: a) The protective conductor of the associated flexible

Page | 133

17th Edition Training Manual cable is of a cross-sectional area not less than 2.5mm2

iii) Two individual protective conductors, each

for plugs rated at 16A and not less than 4 mm2 for

complying with the requirements of Section 543. The

plugs rated above 16A, or

two protective conductors may be of different types

b) The protective conductor of the associated flexible cable is of a cross-sectional area not less than that of the phase conductor. 3) A protective conductor complying with Section 543 with an earth monitoring system to BS 4444 installed which, in the event of a continuity fault occurring in the protective conductor, automatically disconnects the supply to the equipment. 543.7.1.103 — The wiring of every final circuit and distribution circuit intended to supply one or more items of equipment, such that the total protective conductor current is likely to exceed 10 mA, shall have a high integrity protective connection complying with one or more of the following:

e.g. a metallic conduit together with an additional conductor of a cable enclosed in the same conduit. Where the two individual protective conductors are both incorporated in a multicore cable, the total cross-sectional area of all the conductors including the live conductors shall be not less than 10 mm2. One of the protective conductors may be formed by the metallic sheath, amour or wire braid screen incorporated in the construction of the cable and complying with Regulation 543.3.5. iv) An earth monitoring system to BS 4444 may be installed which, in the event of a continuity fault occurring in the protective conductor, automatically disconnects the supply to the equipment. v) Connection of the equipment to the supply by means

A single protective conductor having a cross-

of a double wound transformer or equivalent unit,

sectional area of not less than 10 mm2, complying

suchas a motor-alternator set, the protective

with the requirements of Regulations 543.2 and 543.3

conductor of the incoming supply being connected to

ii) A single copper protective conductor having a cross-

the exposedconductive-parts of the equipment and to

i)

sectional area of not less than 4mm2, complying with

a point of the secondary winding of the transformer

the requirements of Regulations 543.2 and 543.3, the

or equivalent device. The protective conductor(s)

protective conductor being enclosed to provide

between the equipment and the transformer or

additional protection against mechanical damage, for

equivalent device shall comply with one of the

example, within a flexible conduit.

arrangements described in (i) to (iv) above.


Page | 134

17th Edition Training Manual 543.7.1.4 — Where two protective conductors are used in accordance with Regulation 543.7.1.103 (iii), the ends of the protective conductors shall be terminated independently of each other at all connection points throughout the circuit, e.g. the distribution board, junction boxes and socket-outlets. This requires an accessory to be provided with two separate earth terminals. Socket outlet final circuits 543.7.2.101 — For a final circuit with a number of socketoutlets or connection units intended to supply several items of equipment, where it is known or reasonably to be expected that the total protective conductor current in normal service will exceed 10 mA, the circuit shall be provided with a high integrity protective conductor connection complying with the requirements of Regulations 543.7.1 The following arrangements of the final circuit are acceptable: i)

connection to the metal conduit or ducting; or c. Where two or more similar radial circuits supply socket-outlets in adjacent areas and are fed from thesame distribution board, have identical means of short-circuit and overcurrent protection and circuit protective conductors of the same cross-sectional area, then a second protective conductor may be provided at the final socket-outlet on one circuit by connection to the protective conductor of the adjacent circuit. Any equipment or circuits having a protective conductor current greater than 3.5 mA may increase the risk of electric shock. There are therefore, additional requirements stipulated for these circuits.

A ring final circuit with a ring protective conductor. Spurs, if provided, require high integrity protective conductor connection complying with the requirements of Regulation 543.7.1

ii) A radial final circuit with a single protective conductor: a. The protective conductor being connected as a ring; or b. A separate protective conductor being provided at the final socket-outlet by


Page | 135

17th Edition Training Manual 543.7.1.104 — Where two protective conductors are used NOTE: The ends of protective conductors to be terminated independently; the same is true at distribution boards

Fig. 51 Protective conductors separately terminated


Page | 136

17th Edition Training Manual High protective conductor current — Labelling A label or similar information should be provided at the distribution board, indicating those circuits having a high protective conductor current.

Fig. 52 Sample label

Fig. 53 High protective current for sensitive equipment


Page | 137

17th Edition Training Manual 544 — Protective Bonding Conductors

544.1.1 — Except where PME conditions apply, a main equipotential bonding conductor shall have a cross-sectional area not less than half the cross-sectional area required for the earthing conductor of the installation and not less than 6 mm2. The cross-sectional area need not exceed 25mm2 if the bonding conductor is of copper or a cross-sectional area affording equivalent conductance in other metals. The minimum copper equivalent cross-sectional area is given by a copper bonding conductor of the tabulated crosssectional area or a bonding conductor of another metal affording equivalent conductance. 544.1.2 — The main equipotential bonding connection to any gas, water or other service shall be made as near as practicable to the point of entry of that service into the premises. Where there is an insulating section or insert at that point, or there is a meter, the connection shall be made to the consumer’s hard metal pipework and before any branch pipework. Where practicable the connection shall be made within 600 mm of the meter outlet union or at the point of entry to the building if the meter is external.544.2 — Supplementary bonding conductor sizes


Page | 138

17th Edition Training Manual Cross-sectional area of main bonding conductors

The purpose of main equipotential bonding was discussed previously in Chapter 41 (Section 411). The requirements for the minimum cross-sectional area (csa) of a main protective bonding conductor are given in Regulation 544.1.1 and (for PME conditions) Table 54.8, main bonding conductors buried in the ground are subject to additional requirements. Where PME conditions do not apply, a main bonding conductor should have a csa of not less than half that

required for the earthing conductor of the installation and not less than 6 mm2. NOTE: The csa need not exceed 25 mm2 if the bonding conductor is made of copper or, if of other metals, a csa affording equivalent conductance. Where Protective Multiple Earthing (PME) conditions apply, the main bonding conductors should be selected in accordance with the neutral conductor of the incoming supply and Table 54.8. should be followed.

Supplementary Bonding

544.2 — Supplementary bonding conductors 544.2.1 — A supplementary bonding conductor connecting two exposed-conductive-parts shall have a conductance, if sheathed or otherwise provided with mechanical protection, not less than that of the smaller protective conductor connected to the exposed-conductive-parts. If mechanical protection is not provided, its cross-sectional area shall be not less than 4 mm2. Bonding Conductor Regulations: 544.2.1 544.2.2 544.2.3

Sheathed or Mechanically protected

Two Exposed Conductive Parts

An Exposed Conductive Part and anExtraneous Conductive Part

Two Extraneous Conductive Parts

Yes

CSA ≥ CSA of smallest CPC

CSA ≥ CSA of smallest CPC

CSA ≥ 2.5mm2

No

CSA ≥ 4mm2

CSA ≥ 4mm2

CSA ≥ 2.5mm2

Table 15 Representation by table of Regulations 544.2.1, .2, .3 relating to supplementary bonding conductor sizes


Page | 139

17th Edition Training Manual 544.2.2 — A supplementary bonding conductor connecting an exposed-conductive-part to an extraneous-conductivepart shall have a conductance, if sheathed or otherwise provided with mechanical protection, not less than half that of the protective conductor connected to the exposedconductive-part. If mechanical protection is not provided, its cross-sectional area shall be not less than 4 mm2. 544.2.3 — A supplementary bonding conductor connecting two extraneous-conductive-parts shall have a cross-sectional area not less than 2.5 mm2 if sheathed or otherwise provided with mechanical protection or 4 mm2 if mechanical protection is not provided, except that where one of the extraneous-conductive-parts is connected to an exposedconductive-part in compliance with Regulation 544.2.2, that regulation shall apply also to the conductor connecting the two extraneous-conductive-parts.

appliance, the protective conductor can provide both circuit protective conductor and supplementary bonding conductor functions Supplementary bonding was covered in Section 415 (Additional protection). Its use may be required where disconnection times cannot be met or where required due to the special nature of the installation.

Connections to extraneous-conductive-parts

Main bonding connections to metal pipewrk should normally be made using bonding clamps complying with BS 951: Specification for clamps for earthing and bonding purposes.Clamps should be selected to suit both the pipe diameter and bonding conductor size.

544.2.4 — Except where Regulation 544.2.5 applies, supplementary bonding shall be provided by a supplementary conductor, a conductive part of a permanent and reliable nature, or by a combination of these. 544.2.5 — Where supplementary bonding is to be applied to a fixed appliance which is supplied via a short length of flexible cord from an adjacent connection unit or other accessory, incorporating a flex outlet, the circuit protective conductor within the flexible cord shall be deemed to provide the supplementary bonding connection to the exposed-conductive-parts of the appliance, from the earthing terminal in the connection unit or other accessory. Where a short flexible cord is used to connect a fixed © 2008-2015 Electacourse

Fig. 54 Earth clamp

Page | 140


Fig. 55 Supplementary bonding conductors and clamps


Page | 141

17th Edition Training Manual Ch55 - Other Equipment Other equipment: low voltage generating sets, rotating machines, accessories, current using equipment, transformers and luminaires and lighting installations.

551 — Low voltage generating sets

Section 551 applies to both low voltage and extra-low voltage installations which incorporate generating sets intended to supply, either continuously or occasionally, all or part of the installation.

Requirements are included for: •

Supply to an installation which is not connected to a system for distribution of electricity to the public

•

Supply to an installation as an alternative to a system for distribution of electricity to the public

•

Supply to an installation in parallel with a system for distribution of electricity to the public

•

or an appropriate combination of the above

The ESQCR (2002) (Electricity Safety, Quality and Continuity Regulations) will need to be referred to for additional requirements When designing or installing generators special consideration needs to be given to the prospective shortcircuit current and prospective earth fault current for each source as well as: •

Capacity and operating characteristics

•

Overcurrent protection

•

Fault protection

•

Synchronizing (if operating in parallel)

•

Locking-off/interlock devices

Additional requirements where a generating set provides a supply as a switched alternative: Fig. 56 Low voltage portable generator


To prevent parallel operation, suitable precautions may include an electrical, mechanical or electro-mechanical interlock between the operating mechanisms or control circuits of the changeover switching devices.

Page | 142

17th Edition Training Manual Additional requirements where a generating set may operate in parallel with other sources: •

Several additional requirements are required for installations where the generating set may operate in parallel with the system for distribution of electricity to the public.

•

Where the installation and generating set are NOT permanently fixed, an RCD with a rated residual operating current of not more than 30 mA should

Therefore, motors circuits require additional consideration in relation to their starting currents and control equipment. The starting, and load (running)currents of a motor must be considered when assessing the suitability of the equipment and cables carrying these load currents. Every motor should be fitted with means to prevent automatic restarting after a stoppage due to a drop in voltage or failure of supply, where unexpected restarting of the motor might cause danger

be installed in accordance with Regulation 415.1. The RCD is to protect every circuit!

552 — Rotating machines

All equipment, including cable, of every circuit carrying the starting, accelerating and load currents of a motor shall be suitable for a current at least equal to the full-load current rating of the motor.

Fig. 58 Rotating machine stop switches

Every electric motor having a rating in excess of0.37 kW should be provided with control equipment incorporating means of protection against overload of the motor. Fig. 57 Lathe - a rotating machine


Page | 143

17th Edition Training Manual 553 — Accessories

553.1 — Plug and Socket-outlets Every plug and socket shall comply with the requirements. Except for SELV circuits, it shall not be possible for any pin of a plug to make contact with any live contact while any pin of the plug is completely exposed.

553.2 —Cable couplers A cable coupler shall be arranged so that the connector of the coupler is fitted at the end of the cable remote from the supply.

It shall not be possible for any pin of a plug to make contact with any live contact of any socket-outlet other than the type if its design. Every socket-outlet for household and similar use shall be of the shuttered type. A plug and socket must be installed and used in the voltage it is designed for. A socket on a wall shall be mounted at a height above the floor or surface to minimize any risk of damage to either the socket-outlet or plug and cord during insertion, use or withdrawal of the plug. Where portable equipment is likely to be used, provision should be made so that the equipment can be fed from an adjacent and conveniently accessible socket outlet, taking into account the length of flexible cord normally fitted to appliances and luminaires.

Fig. 59 Extension cable with couplers

554 — Current-using equipment Electrode water heaters or boilers

Used to heat water or raise steam in certain domestic, commercial and industrial applications.They can be either single-phase or three-phase. Typical applications include saunas, central heating, humidifying, heat pumps, cleaning and sterilizing.Electrode boilers can be low voltage, high voltage. Special requirements must be complied with relating to:


Page | 144

17th Edition Training Manual Earthing and bonding, Overcurrent protection, and Isolation and Switching.

554.4 — Heating conductors and cables Heating conductors and cables are specifically designed to generate heat, they are used for: •

Underfloor electric heating in dwellings and other premises (the requirements of Part 7, Section 753 must also be met in this case).

•

Heating of the playing area at out-door sports stadiums.

•

Heating roads and pavements to prevent icing.

•

Soil warming in agricultural and horticultural premises.

•

Industrial heating applications.

•

Trace heating of pipes and vessels.

Fig. 60 A single phase immersion heater is not considered to be an electrode boiler

Water heaters having immersed and uninsulated heating elements.: A single-phase water boiler or heater having an uninsulated heating element immersed in water (ie a kettle) is deemed not to be an electrode water heater or electrode boiler.


Fig. 61 Underfloor heating

Page | 145

17th Edition Training Manual Section 753 states: When installing heating conductors and cables care must be taken to prevent mechanical damage, damage from corrosion, thermal effects to adjacent material and to ensure the system temperature is not exceeded.

covered by specific product or system standards, e.g. the construction of assemblies of electrical equipment to the appropriate part of the BS EN 61439 series.

555 — Autotransformers and step-up transformers

557.3.1 General

Where an autotransformer is connected to a circuit having a neutral conductor, the common terminal of the winding must be connected to the neutral conductor. Where a step-up transformer is used, a linked switch must be provided for disconnecting the transformer from all live conductors of the supply.

New Section 557 - Auxiliary Circuits Section 557 provides regulations concerning auxiliary circuits. Included are three diagrams of how an auxiliary circuit can be supplied (from the main circuit, via a rectifier and via a transformer). The Section lists regulations under the headings listed and finishes with table 55.2 listing the minimum cross-sectional area of copper conductors in mm2. We list below major points relating to this new section, we encourage readers to pay close attention to all the regulations introduced in Section 557 – Auxiliary Circuits. An Auxiliary Circuit is defined as a circuit for transmission of signals intended for control, detection, supervision or measurement of the functional status of a main circuit.

557 Auxiliary Circuits 557.1 Scope

This section applies to auxiliary circuits, except those


557.2 Not used The power supply, a.c. or d.c., for an auxiliary circuit may be either dependent or independent of the main circuit according to its required function. If the status of the main circuit has to be signalled, then the signalling circuit shall be able to operate independently of that main circuit. A control circuit shall be designed, arranged and protected to limit dangers resulting from a fault between the control circuit and other conductive parts liable to cause malfunction (e.g. inadvertent operation) of the controlled equipment. 557.3.2 Power supply for auxiliary circuits dependent on the main circuit 557.3.2.1 General Auxiliary circuits with a power supply dependent on the main a.c. circuit shall be connected to the main circuit: i)

directly (see Figure 55.1), or

ii) via a rectifier (see Figure 55.2), or iii) via a transformer (see Figure 55.3). It is recommended that auxiliary circuits supplying primarily electronic equipment or systems should not be supplied directly but at least via simple separation from the main circuit.

Page | 146

17th Edition Training Manual Fig 55.1 Auxiliary circuit supplied directly from the main circuit

Fig 55.3 – Auxiliary circuit supplied from the main circuit via a transformer

Fig. 64 Auxiliary circuit supplied from the main circuit via a transformer

Fig. 62 Auxiliary circuit supplied directly from the main circuit

Fig 55.2 – Auxiliary circuit supplied from the main circuit via a rectifier

557.3.2.2 Auxiliary circuit supplied from the main circuit via transformer 557.3.3 Auxiliary circuit supplied by an independent source 557.3.4 Auxiliary circuits with or without connection to earth 557.3.4.1 General 557.3.4.2 Earthed auxiliary circuit 557.3.4.3 Unearthed auxiliary circuit 557.3.5 Power supplies for auxiliary circuits 557.3.5.1 General 557.3.5.2 Standby power supply or power supply for safety services

Fig. 63 Auxiliary circuit supplied from the main circuit via a rectifier


557.3.5.3 AC supply

Page | 147

17th Edition Training Manual 557.3.5.4 DC supply

537.3.6.2 Protection against short-circuit

557.3.5.4.1 Supply by a power system

557.4 Characteristics of cables and conductors 557.4.1 Minimum cross-sectional areas

557.3.5.4.2 Supply by batteries 557.3.6 Protective measures 557.3.6.1 Protection of wiring systems Table 55.2 – Minimum cross-sectional area of copper conductors in mm2 Application

Type of cable Single-core Single-wire

Stranded

Two-core Screened

Unscreened

Multi-core Screened or unscreened

Control circuitsa

0.5

0.5

0.5

0.5

0.1

Data transfer

-

-

-

-

0.1

Other auxiliary circuits may need a larger cross-sectional area of copper conductors, e.g. for measuring a

Note The cross sectional area of copper conductors is derived from Section 524


Page | 148

17th Edition Training Manual 559 — Luminaires and lighting installations

Section 559 applies to luminaires (lighting fittings) and lighting installations intended to be part of the fixed installation. Note: With effect from Amendment 3 regulations relating to highway power supplies and street furniture have moved to Special Locations 714. Excluded are •

High voltage signs supplied at low voltage (such as neon tubes).

•

Signs and luminous discharge tube installations operating from a no-load rated output voltage exceeding 1 kV but not exceeding 10 kV (BS EN 50107).

•

temporary festoon lighting.

559.4 — Luminaires - Protection against fire This section deals with the thermal effects of radiant energy on the surroundings of a luminaire, to be taken into account is: •

The maximum permissible power dissipated by the lamps

•

The fire-resistance of the adjacent material both at the point of installation and in the thermally affected areas

•

The minimum distance to combustible material, including in the path of a spotlight beam


559.5.1.1 — Connection to the fixed wiring At each fixed lighting point or position, one of the connection devices listed below must be used for the connection of the luminaires: •

A ceiling rose to BS 67

•

A LSC to BS 6972 or BS 7001

•

A batten lamp holder or pendant set to BS EN 60598

•

A luminaire to BS EN 60598

•

A suitable socket-outlet to 1363-2, BS 546 or BS EN 60309-2

•

A plug-in lighting distribution unit to BS 5733

•

A connection unit to BS 1363-4

•

Appropriate terminals enclosed in a box complying with BS EN 60670 or BS 4662

•

A device for connecting a luminaires (DCL) to IEC 61995.1

559. 5.1.201 A ceiling rose or lampholder shall not be installed in any circuit operating at a voltage normally exceeding 250 volts. 559. 5.1.202 A ceiling rose shall not be used for the attachment of more than one outgoing flexible cable unless it is specially designed for multiple pendants. 559. 5.1.203 Luminaire supporting couplers and devices for the connection of luminaires are designed specifically for the electrical connection of luminaires and shall not be used for

Page | 149

17th Edition Training Manual the connection of any other equipment. 559. 5.1.204 Lighting circuits incorporating B15, B22, E14, E27 or E40 lampholders shall be protected by an overcurrent protective device of maximum rating 16A. 559. 5.1.205 Bayonet lampholders B15 and B22 shall comply with BS EN 61184and shall have the temperature rating T2 described in that standard. 559.5.1.206 In circuits of a TN or TT system, except for E14 and E27 lampholders complying with BS EN 60238, the outer contact of every Edison screw or single centre bayonet cap type lampholder shall be connected to the neutral conductor. This regulation also applies to track mounted systems. 559. 5.1.207 A lighting installation shall be appropriately controlled.

559.5.1.208 Consideration shall be given to the provision of the neutral conductor, at each switch position, to facilitate the installation of electronic switching devices. 559.5.2— Fixing of luminaire Luminaires must be fixed securely, and the means of fixing must be able to support the weight of the luminaires, this fixing must be able to carry a mass of not less than 5 kg. If the mass of the luminaires is greater than 5kg, then the installer must ensure the fixing means can support the weight of the luminaires. Any flexible cables between the fixing means and the luminaires should be installed to accommodate any expected stress in the conductors or terminals so as not to impair the safety or operation of the luminaires 559.6.3 — Through wiring Through wiring is only permitted if the luminaires are designed for that purpose. For luminaires complying with BS EN 60598, but with no temperature markings, heat resistant cables are not required. Luminaires to this standard with temperature marking will require suitable heat resisting cables. Where no information is provided, heat-resisting cables and/or insulated conductors of type H05S-U, H05S-K, H05SJK, H05SS-K (BSEN 50525series) or equivalent shall be used.

Fig. 65 Ceiling rose – pay regard to the particular requirements concerning ceiling lights and lampholders


Page | 150

17th Edition Training Manual Selection of symbols used in Section 559 (Table 55.2)

Fig. 66 Symbols used in 559 Table 55.3 of BS7671


Page | 151

17th Edition Training Manual Ch56 - Safety services (Sources, circuits and wiring systems) A Safety Service is defined as: ‘An electrical system for electrical equipment provided to protect or warn persons in the event of a hazard, or essential to their evacuation from a location’

560.1 — Scope

This chapter covers the requirements for the installation of Safety Services and Standby supply services are outside the scope of this Chapter. •

Safety services include:

•

Emergency lighting

•

Fire pumps

•

Fire rescue service lifts

•

Fire detection and alarm systems

•

CO2 detection and alarm systems

•

Fire evacuation systems

•

Smoke ventilation systems,

•

Fire service communication systems

•

Essential medical systems

•

Industrial safety services

Fig. 67 Fire safety equipment


Page | 152

17th Edition Training Manual Additional specialist systems classed as safety services also include: •

It is normally the case that safety service systems will be required to operate at times of “mains failure” and also continue their effective operation through the harsh environment of a fire condition.

•

It is imperative that these potential life-saving installations have adequate consideration given for their design, installation and continued verification (via regular inspection and testing) to ensure that they have and maintain, the appropriate level of operational integrity.

The requirements for the general characteristics relating to these systems are specified within Chapter 35. Four distinct sources are recognized as being suitable for use as the safety service. •

storage batteries

•

primary cells

•

generator sets independent of the normal supply

•

a separate feeder of the supply network effectively independent of the normal feeder

The integrity of the electrical source is of paramount importance and as such must be of appropriate capacity capable of supplying the total load and installed as fixed equipment, located in an area that is only accessible to appropriate personnel.


The majority of safety sources take the form of either a dedicated, constantly charged battery, or a combination of battery and generator set. However, the less common system of separate independent feeder supplies is also recognized, providing appropriate assurance is obtained from the supplying network or networks that these supplies are unlikely to fail concurrently. 560.4 — Classifications An electrical safety service supply is classified as either: i)

A non-automatic supply (initiated by an operator)

ii) An automatic supply (independent of an operator) Automatic systems are further classified by whether they offer a continuous “no-break” supply, or are based on their maximum changeover time duration: iii) No break iv) Very short break v) Short break vi) Normal break (was lightning break pre - AM1) vii) Medium break viii)

Long break

a short break An automatic supply available between 0.15 s and 0.5 s. a medium break An automatic supply available within 15s.

Page | 153

17th Edition Training Manual 560.6 — Electrical Sources for safety services

type, comply with BS EN 62040.

560.6.2 — Electrical sources for safety services shall not be affected by the failure of the normal service.

560.6.13 — Generator supply sourcesA generator supply source will comply with BS 7698-12

560.6.3 — Electrical sources for safety services will be located in a location only accessible by a skilled or instructed person. 560.6.4 — Electrical sources for safety services will be located in a adequately ventilated location to prevent the exhaust gases, smoke of fumes from contaminating the area where there is an occupied area. 560.6.5 — Separated independent feeders from a distributor’s network shall not serve as electrical sources for safety services unless assurance can be obtained that the 2 supplies are unlikely to fail concurrently. 560.6.10 — Central power supply sources for safety services.: Batteries used in a central battery system will have a design life of 10 years and comply with the standards in 560.6.10 560.6.11 — Batteries used in a low power supply system will have a design life of 5 years and comply with the standards in 560.6.11A low power supply system is limited to 500W for 3 hours duration or 1500W for 1hour duration. 560.6.12 — Uninterruptible power supply sources (UPS). Where an uninterruptible power supply is used, it shall: •

Operate distribution circuit protective devices.

•

Start the safety devices.

Fig. 68 Illuminated fire exit sign

Uninterruptible power supply systems should comply with the requirements of Regulation 560.6.10 and if of the static


Page | 154

17th Edition Training Manual 560.7 — Circuits of safety services In addition to the requirements relating to cables, specific requirements also relate to: •

Overload protection switchgear and controlgear locations routes of wiring systems.

•

The required minimum operational design life of batteries should be in accordance with BS EN 50171, with a minimum declared life of (1) 10 years for central power supply sources and (2) 5 years for low power supply sources.

Drawings and information relating to all (safety

Circuits for safety services.

service) current-using equipment

To ensure a high integrity supply and to minimize disruption (electrical faults, maintenance or modification to other systems) a safety service should employ a dedicated independent circuit that is ideally run through areas of low fire and risk.

Batteries used as the supply for safety services are classified into two categories: ‘Central power supply sources’ and‘Low power supply sources’, the low power source being limited to 1500 watthours.


Where impracticable, a circuit should be run using a fireresistant cable system

Page | 155

17th Edition Training Manual REVIEW QUESTIONS – Selection and erection of equipment Question 1

Question 3

Every item of equipment shall be suitable for the design current, taking into account any capacitive and inductive effects, and

What is the minimum cross-sectional area for aluminium non-sheathed and sheathed cables used in power circuits? A.

40 mm2

A.

the current likely to flow in abnormal conditions for such periods of time as are determined by the characteristics of the protective devices concerned.

B.

10 mm2

C.

30 mm2

B.

overload current

D.

16 mm2

C.

the maximum current in abnormal conditions for such periods of time as are determined by the characteristics of the protective devices concerned.

Question 4

D.

the maximum current in abnormal conditions for any period of time.

A heating cable intended for laying directly in soil, concrete, cement screed or other material used for road and building construction shall be A.

capable of withstanding mechanical damage under the conditions that can reasonably be expected to prevail during its installation

B.

constructed of material that will be resistant to damage from dampness and/or corrosion under normal conditions of service

C.

either the first two answers

D.

both the first two answers

Question 2 What type of cables necessarily must be enclosed in conduit, ducting or trunking? A.

Sheathed cables for fixed wiring.

B.

Sheathed cables for temporary wiring.

C.

Non-sheathed cables for fixed wiring.

D.

Non-sheathed cables for temporary wiring.


Page | 156


Question 8

Bare conductors may be used for extra-low voltage lighting installations If their nominal voltage does not exceed A.

15 V a.c. or 40 V d.c.

Where a generating set is used as an additional source of supply in parallel with other sources, protection shall remain effective in all situations against overcurrent and

B.

25 V a.c. or 60 V d.c.

A.

harmonic distortion

C.

60 V a.c. or 25 V d.c.

B.

high protective conductor currents

D.

25 V a.c. and 25 V d.c.

C.

unbalance

D.

thermal effects

Question 6 If a cable is buried in a wall less than 50mm depth and is not protected by metallic enclosures, the additional protection required is

Question 9

A.

RCD protection

Identify which one of the following sources for safety services are recognised the IET Wiring Regulations incorporating Amendment 1

B.

MCB protection

A.

primary cells

C.

supplementary bonding

B.

generator set dependent on the normal supply

D.

external notification of cable routes

C.

secondary cells

D.

solar energy cells

Question 7 The maximum operating temperature of standard general purpose thermoplastic PVC cable is A.

50°

B.

75°

C.

110°

D.

70°


Question 10 Identify which one of the following sources for safety services are recognised by BS7671 A.


B.

secondary cells

C.

parallel feeder to the normal feeder from the supply network

D.

storage batteries

Page | 157

17th Edition Training Manual ANSWERS – Selection and erection of equipment

1A, Ref: BS7671: 512.1.2 2C, Ref: BS7671: 521.10.1 3D, Ref: BS7671: 524.2.3 4D, Ref: BS7671: 554.4.2 5B, Ref: BS7671: 715.521.106 6A, Ref: BS7671: 522.6.202 7D, Ref: BS7671: 523.1 8D, Ref: BS7671: 551.7.1 9A, Ref: BS7671: 560.6.1 10D, Ref: BS7671: 560.6.1


Page | 158


PART 6 — INSPECTION & TESTING

Overview Part 6, which was Part 7 in the 16th Edition, covers the requirements for Inspection & Testing. Chapter 61: Initial Verification — Inspection 611 and Testing 612 Chapter 62: Frequency of Inspection and Testing Chapter 63: Certification and Reporting This section of the 17th Edition Course is intended to be informative only; the comprehensive understanding of Inspection and Testing of Electrical Installations must be obtained from a recognized certifiable course which satisfies


legislative requirements. This section covers those regulations that relate to Inspection and Testing and which of those regulations you may expect to be asked about in the 2382-15 exam. The fundamental reason for inspection and testing an electrical installation is to determine whether new installation work is safe to put into service, or whether an existing installation is safe to remain in service until the next inspection date. IET Guidance Notes 3 (GN3), is the essential companion for inspectors and testers

Page | 159

17th Edition Training Manual Ch 61 - Initial Verification Initial verification (inspection and testing) is used to ensure that electrical installations are safe before being put into service. 610.1 — Every installation shall, during erection and on completion before being put into service, be inspected and tested to verify, so far as is reasonably practicable, that the requirements of the Regulations have been met. Precautions shall be taken to avoid danger to persons and damage to property and installed equipment during the inspection and testing. Three principle criteria for an electrical installation which informs initial verification and inspection: 1. compliance with BS 7671, particularly in reference to: a. The Fundamental Principles (Section 131) b. The general characteristics (Sectiosn 311 and 313) c. Information required by 514.9.1 2. compliance with the project specification (commissioning) 3. that it is safe to use.

Avoid Danger to Persons •

•


Have you checked to see if any essential services are supplied from the board e.g. emergency lighting, fire alarms, life-support equipment, UPS systems, gas monitoring systems, etc.? Have you isolated the circuit correctly?

Page | 160

17th Edition Training Manual • • • •

Have you discharged any capacitors? Is the test equipment appropriate for the environment, e.g. intrinsically Safe? Are you using long test leads that could cause people to trip over? Have you informed people of the dangers?

Avoid Damage to Property • • • • • • •

Is there an RCD in the circuit? Are there computers on line? Is there electronic equipment in the circuit? Could gaskets be damaged when removing covers? Are all the loads disconnected? Is there any equipment or processes which may be damaged if disconnected for long periods of time? Is there any essential equipment which cannot be turned off?

610.5 - The verification shall be made by a skilled person, or persons, competent in such work..

(this may be ascertained by mark or by certification furnished by the installer or by the manufacturer), and •

Correctly selected and erected in accordance with the Regulations, and

•

Not visibly damaged or defective so as to impair safety.

611.3 — The inspection shall include at least the checking of the following items where relevant, including as appropriate all particular requirements for special installations or locations (Part 7). •

Connection of conductors

•

Identification of conductors

•

Routing of cables in safe zones or protection against mechanical damage, in compliance with Section 522

•

Selection of conductors for current-carrying

This replaces the reference to competent person.

capacity and voltage drop, in accordance with the

611 — Inspection

design

611.1 — Inspection shall precede testing and shall normally be done with that part of the installation under inspection disconnected from the supply. 611.2— The inspection shall be made to verify that the installed electrical equipment is: • In compliance with Section 511


•

Connection of single-pole devices for protection or switching in phase conductors only

•

Correct connection of accessories and equipment

•

Presence of fire barriers, suitable seals and protection against thermal effects

•

Methods of protection against electric shock covered in detail earlier in this course.

Page | 161

17th Edition Training Manual Summary of Initial verification

1. Precedes testing and the installation being inspected should be disconnected from the supply. 2. Is necessary before any new installation work or alterations and additions to existing installations are permanently connected to the supply. 3. Confirms that equipment: 4. Complies with UK or European standards (BS, BS EN) 5. Is correctly selected and erected, and 6. Is not damaged or defective as to impair safety.

A Schedule of items inspected should be completed to ensure all relevant requirements have been met.

612 — Testing

This section details the required tests to be for initial verification. The tests should be carried out in a prescribed sequence, some prior to the circuits being energized. 612.1 The tests of Regulations 612.2 to 13, where relevant, shall be carried out and the results compared with relevant criteria. Measuring instruments and monitoring equipment and methods shall be chosen in accordance with the relevant parts of BS EN 61557. If other measuring equipment is used, it shall provide no less degree of performance and safety. When undertaking testing in a potentially explosive atmosphere, appropriate safety precautions in accordance with BS EN 60079-17 and BS EN 61241-17 are necessary. The tests of Regulations 612.2 to 6, where relevant, shall be carried out in that order before the installation is energized. Where the installation incorporates an earth electrode, the test of Regulation 612.7 shall also be carried out before the installation is energized. If any test indicates a failure to comply, that test and any preceding test, the results of which may have been influenced by the fault indicated, shall be repeated after the fault has been rectified. Before the supply is energized – Dead tests 612.2

Fig. 69 Continuity of conductors


Continuity of Conductors

612.2.1 Continuity of protective conductors including main and supplementary equipotential bonding

Page | 162

17th Edition Training Manual 612.2.2 Continuity of ring final circuit conductors

612.5

Insulation resistance/impedance of floors and walls

612.3

612.6

Polarity

Insulation resistance

Fig. 71 Polarity test (part)

Fig. 70 Single phase insulation resistance

612.4

Protection by SELV, PELV or Electrical separation

612.7

Earth electrode resistance

612.4.1 Protection by SELV 612.4.2 Protection byPELV 612.4.3 Protection by Electrical separation 612.4.4 FELV 612.4.5 Basic protection by barriers and enclosures provided during erection


Page | 163

17th Edition Training Manual preceding test, the results of which may have been influenced by the fault indicated, shall be repeated after the fault has been rectified. It is recommended you become familiar with each of the tests describe in Section 612, and to be prepared to refer to Table 61.

Ch62 - Periodic Inspection & Testing Periodic testing is not the same as testing as part of an Initial Verification. The same range and level of testing is not required and in the majority of cases will not be possibleThe two Regulations which you should pay attention to are:

Fig. 72 Earth electrode test (one of many)

With the electrical supply connected 612.8

Protection by ADS

612.9

Earth fault loop impedance

612.10 Additional Protection(RCDs) 612.11 Prospective Fault current 612.12 Check for Phase Sequence (multi-phase supply) 612.13 Functional Testing 612.14 Verification of Voltage drop

621.1 — Where required, periodic inspection and testing of every electrical installation shall be carried out in accordance with regulations 621.2 to 621.5 to determine, as is reasonably practical, whether the installation is in a satisfactory condition for continued service. 621.2 — Inspection comprising careful scrutiny of the installation shall be carried out without dismantling or with partial dismantling as required, together with the appropriate tests of Chapter 61. Such inspection and testing shall provide, so far as is reasonably practicable, for: •

The safety of persons and livestock against the effects of electric shock and burns.

•

Protection against damage to property by fire and heat arising from an installation defect, and

If any test indicates a failure to comply, that test and any


Page | 164


Confirmation that the installation is not damaged or deteriorated so as to impair safety, and

•

The identification of installation defects and noncompliance with the requirements of the Regulations which may give rise to danger.

621.3— Precautions shall be taken to ensure that the inspection and testing does not cause danger to persons or livestock and does not cause damage to property and equipment even if the circuit is defective. 621.5— Periodic inspection and testing shall be undertaken by a competent person 622 — Frequency of Inspection and Testing 622.1 — The frequency of periodic inspection and testing of an installation shall be determined having regard to the type of installation, its use and operation, the frequency and quality of maintenance and the external influences to which it is subjected. The results and recommendations of the previous report if any shall be taken into account. 622.2 — In the case of an installation under effective management systemfor preventive maintenance in normal use, periodic inspection and testing may be replaced by an adequate regime of continuous monitoring and maintenance of the installation by skilled persons, competent in such work Appropriate records shall be kept.


Ch 63 - Certification & Reporting 631.1 — Upon completion of the verification of a new installation or changes to an existing installation, an Electrical Installation Certificate, based on the model given in Appendix 6, shall be provided. Such documentation shall include details of the extent of the installation covered by the Certificate, together with a record of the inspection, the results of testing and a recommendation for the interval until the first periodic inspection. 631.2 — Upon completion of the periodic inspection and testing of an existing installation, an Electrical Installation Condition Report, based on the model given in Appendix 6, shall be provided. Such documentation shall include details of the extent of the installation and limitations of the inspection and testing covered by the Report, together with records of inspection, the results of testing and a recommendation for the interval until the first periodic inspection. 631.3 — Where minor electrical installation work does not include the provision of a new circuit, a Minor Electrical Installation Works Certificate, based on the model given in Appendix 6, shall be provided for each circuit altered or extended. 631.4 — Electrical Installation Certificates, Electrical Installation Condition Reports and Minor Electrical Installation Works Certificates shall be compiled and signed or otherwise authenticated by skilled persons, competent to verify that the requirements of the standard have been met.

Page | 165

17th Edition Training Manual 631.5 — Electrical Installation Certificates, Electrical Installation Condition Reports and Minor Electrical Installation Works Certificates may be produced in any durable medium, including written and electronic media. Regardless of the media used for original certificates, reports or their copies, their authenticity and integrity shall be verified by a reliable process or method. The process or method shall also verify that any copy is a true copy of the original.

632 — Initial Verification

632.1 —Following the initial verification required by Chapter 61, an Electrical Installation Certificate, together with a schedule of inspections and a schedule of test results, shall be given to the person ordering the work. These schedules shall be based upon the models given in Appendix 6. 632.2 — The schedule of test results shall identify every circuit, including its related protective device(s), and shall record the results of the appropriate tests and measurements detailed in Chapter 61. 632.3 — The person or persons responsible for the design, construction, inspection and testing of the installation shall, as appropriate, give to the person ordering the work a Certificate which takes account of their respective responsibilities for the safety of that installation, together with the schedules described in Regulation 632.1. Fig. 73 Sample Electrical Installation Condition


632.4 — Defects or omissions revealed during inspection and testing of the installation work covered by the Certificate

Page | 166

17th Edition Training Manual shall be made good before the Certificate is issued.

633 — Alterations and Additions

633.1 — The requirements of Sections 631 and 632 for the issue of an Electrical Installation Certificate or a Minor Electrical Installation Works Certificate shall apply to all the work of the alterations or additions. 633.2 — The contractor or other person responsible for the new work, or a person authorized to act on their behalf, shall record on the Electrical Installation Certificate or the Minor Electrical Installation Works Certificate, any defects found, so far as is reasonably practicable, in the existing installation.

634 — Periodic Inspection and Testing

634.1 — Following the periodic inspection and testing described in Chapter 62, an Electrical Installation Condition Report, together with schedules of inspection and schedules of test results shall be given by the person carrying out the inspection, or a person authorized to act on their behalf, to the person ordering the inspection. These schedules shall be based upon the models given in Appendix 6. The schedule of test results shall record the results of the appropriate tests required by Chapter 61. 634.2 — Any damage, deterioration, defects, dangerous conditions, and non-compliance with the requirements of the Regulations which may give rise to danger, together with any limitations of the inspection and testing shall be recorded.


Page | 167

17th Edition Training Manual REVIEW QUESTIONS – Inspection and Testing Question 1

Question 3

Any insulation or insulating arrangement of extraneousconductive-parts intended to satisfy Regulation 418.1,4(iii) if

On a residual current device, the purpose of the integral test button is to check

A.

A.

the mechanical function

B.

the electrical function

C.

the rating

D.

the disconnection time

B.

when tested at 500 V d.c. shall be not less than 1 megohm shall be able to withstand a test voltage of at least 2 kV a.c. rms

C.

shall not pass a leakage current exceeding 1 mA in normal conditions of use

D.

all the written answers

Question 2 Which one is NOT a subject of periodic inspection? A.

protection against damage to property by fire and heat arising from an installation defect

B.

confirmation that the installation satisfies efficiency requirements

C.

safety of persons and livestock against the effects of electric shock and bums

D.

confirmation that the installation is not damaged or deteriorated so as to impair safety


Question 4 The minimum value of insulation resistance test performed on a PELV installation is A.

9.0MΩ

B.

5.5MΩ

C.

0.2MΩ

D.

0.5MΩ

Page | 168


Question 8

An insulation resistance test performed on a PELV installation should be capable of producing a test voltage of

Before conducting an insulation resistance test you should A.

ensure that the polarity is correct

A.

250v d.c.

B.

ensure correct RCDs are fitted

B.

500v d.c.

C.

C.

250v a.c.

ensure that the earth fault loop impedance is satisfactory

D.

50v d.c.

D.

ensure that all lamps are removed

Question 6

Question 9

On a 230v a.c. installation, the minimum value of insulation resistance is

An insulation resistance test performed on a 230v a.c.installation should be capable of producing a test voltage of

A.

10.0MΩ

B.

2.0MΩ

C.

1.0MΩ

D.

0.5MΩ

Question 7 An electrical installation certificate should be signed by

A.

500 V a.c.

B.

1000 V d.c.

C.

50 V d.c.

D.

500 V d.c.

Question 10

A.

the customer

B.

the local authority

The most convenient method of determining the value of the prospective short circuit current at the origin of an existing installation would be by

C.

the REC

A.

functional testing

D.

a skilled person

B.

measurement

C.

calculation

D.

inspection


Page | 169


ANSWERS – Inspection and Testing

1D, Ref: BS7671: 612.5.2 2B, Ref: BS7671: 621.2 3A, Ref: BS7671: 612.13.1 4D, Ref: BS7671: 612.3.2 5A, Ref: BS7671: 612.3.2 6C, Ref: BS7671: 612.3.2 7D, Ref: BS7671: 610.6, 610.5 8D, Ref: BS7671: 612.3.2 9D, Ref: BS7671: 612.3.2 10B, Ref: BS7671: 612.11


Page | 170


MODULE 5 - PART 7 — SPECIAL INSTALLATIONS OR LOCATIONS

movement

Overview Section 700:

General

Section 701:

Locations containing a bath or shower

Section 702:

Swimming pools and other basins

Section 703:

Rooms and cabins containing sauna heaters

Section 704:

Construction and demolition site installations

Section 705:

Agricultural and horticultural premises

Section 706:

Conducting locations with restricted


Section 708: Electrical installations in caravan / camping parks and similar locations Section 709:

Marinas and similar locations

Section 710:

Medical locations *

Section 711:

Exhibitions, shows and stands

Section 712:

Solar photovoltaic (pv) power supply systems

Section 717:

Mobile or transportable units

Page | 171

17th Edition Training Manual Section 721: caravans

Electrical Installations in caravans and motor

Section 729:

Operating and maintenance gangways *

701.1 — Such locations and the surrounding area are considered to be locations where there is an increased risk of electric shock due to: A reduction in body resistance caused either by

Section 740: Temporary electrical installations for structures, amusement devices and booths at fairgrounds, amusement parks and circuses

• •

Absence of or minimal clothing and

Section 753:

•

Likely contact of substantial areas of the body with

Floor and ceiling heating systems

*Sections 710 and 729 are new for the 17th Edition. Section 710 was also completely updated by the Corrigendum published in June 2013

Section 701 - Locations containing a bath or shower Pay great attention to understanding the Regulations concerning bathrooms. A strong understanding will enable you to answer the inevitable exam questions quickly. Easy marks.

bodily immersion or by wet skin

earth potential. Classification of external influence Zone 0 -The interior of the bath tub or shower Zone 1 - The area up to 2.25m high above the bath tub, or the highest point of the shower head/water outlet; the area circumscribing the bath tub or shower, a distance within 1.2m of the water outlet on the wall or ceiling for showers without a basin Zone 2 — The area above 2.25m; the area which is greater than 0.6m from the Zone 1 border. Zonal concept is based on the perceived risk of electric shock in relation to areas in/around the bath etc. Having established the zones, particular requirements are then prescribed for: Switchgear, Controlgear,Accessories and Current using equipment

Fig. 74 If only all bathrooms were like this


Page | 172


Zone 0 - The interior of the bath tub or shower Zone 1 - The area up to 2.25m high above the bath tub, or the highest point of the shower head/water outlet; the area circumscribing the bath tub or shower, a distance within 1.2m of the water outlet on the wall or ceiling for showers without a basin Zone 2 - The area above 2.25m; the area which is greater than 0.6m from the Zone 1 border.


Page | 173

17th Edition Training Manual 701.41 — Protection for safety: protection against electric shock 701.410.3.5 — The protective measures of obstacles and placing out of reach is not permitted 701.411.3.3 — Additional protection by RCDs

having the characteristics specified in Regulation 415.1.1 shall be provided for low voltage circuits: i.

serving the location

ii.

passing through zones 1 and/or 2 not serving the location.

Additional protection by RCDs Additional protection by the use of one or more RCDs

Fig. 75 Low voltage circuits passing through the location require RCD protection


Page | 174

17th Edition Training Manual 701.413 — Electrical separation Only to be used for 1 item of equipment or 1 single socket. 701.413 – Extra low voltage provided by SELV or PELV circuits Where SELV or PELV is used basic protection is supplied by basic insulation complying with 416.1 or barriers complying with 416.2 701.415 — Additional protection 701.415.2 — Supplementary equipotential bonding is not necessary where all circuits of the location: •

Comply with requirements for automatic disconnection

•

Are ≤ 30 mA RCD protected, and

•

All extraneous-conductive-parts of the location are connected to the protective equipotential bonding within the installation.

However, if supplementary equipotential bonding, is required supplementary bonding shall be established connecting together the terminals of the protective conductor of each circuit to the accessible extraneousconductive-parts


Page | 175


Fig. 76 Equipotential bonding in a bathroom (three water pipes bonded – 1. Hot water, 2. Cold water, 3. Heating)


Page | 176

17th Edition Training Manual 701.5 Selection and erection of equipment

Electric Showers

Zone 0

IPX7

Zone 1&2

IPX4

Usually suitable for installation within zone 1. Not required by BS 7671 to be protected by an RCD, however, often shower manufacturers recommend an RCD

701.512.2 — External influences Minimum IP codes for:

Where water jets are used for cleaning - IPX5 701.512.3 — Switchgear ZONE 0 No switchgear permitted. Socketoutlets prohibited within 3m of zone 1.

Electric showers and electric shower pumps should comply with BS EN 60335-2-35 and BS EN 60335-2-41 respectively.

Normal practice is to provide isolation switch within the bathroom.The switch must be installed outside zones 0, 1 and 2 although the cord of cord operated switches, may reach into zones 1 or 2.

ZONE 1 SELV switching only ≤ 12V A.C. (source outside zones). ZONE 2 SELV switching & socket-outlets as above and shaver outlets to BSEN 61558-2-5. 701.55 — Current using equipment ZONE 0 — Fixed, permanent connection, SELV & to relevant standard ZONE 1 — Allowed: •

Whirlpool units

•

Electric Showers

•

Shower Pumps

•

SELV (not exceeding 25 V ac)

•

Fans (ventilation equipment)

•

Towel rails

•

Water heaters

•

Luminaires


Fig. 77 Shower isolator switch

Page | 177

17th Edition Training Manual 701.753 — Electric floor heating Where installed in a room containing a bath or shower all heating cables must be of a type incorporating: •

A metal sheath, or

•

Metal enclosure, or

•

Fine mesh metallic grid.

NOTE:In all of the above cases, the metallic sheath, enclosure or grid must be connected to the supply protective conductor (unless SELV) A typical electric floor heating application (covered further in Section 753).

Section 702 - Swimming Pools & Other Basins 702.1 — Scope This particular section applies to the basins of swimming pools, the basins of fountains and the basin of paddling pools; the requirements also apply to the surrounding zones of these basins. In these areas the risk of shock is increased due to: • •

Fig. 78 In scope - swimming pools, Out of scope - beaches

702.32 — Classification of external influences As with bathrooms and shower rooms, the zonal concept is used. The zones for Section 702 have the same names, but do not have the same definitions. Refer to the illustrations. The zone definitions are:

A reduction in body resistance caused either by

Zone 0 — the interior of the basin

bodily immersion or by wet skin, and

Zone 1 — 2m from the rim of the basin and a height of

Likely contact of substantial areas of the body with

2.5m

earth potential.

Zone 2 — 1.5m external to zone 1

Exclusions from Scope:Except for areas designed especially for swimming pools, the requirements of Section702 DO NOT apply to natural waters, lakes or coastal beaches


Zone 2 does not apply to fountains.

Page | 178


Fig. 79 Zone dimensions for swimming pools and paddling pools

r1=2m r2=3.5m

Fig. 80 Zone dimensions for basin above ground


Fig. 81 Plan of zones. See BS7671 Fig 702.3 for details, including where partitions are present

Page | 179

17th Edition Training Manual 702.415.2 — Additional Protection: Supplementary equipotential bonding

sheath of a wiring system shall be connected to the supplementary equipotential bonding.

All extraneous-conductive-parts in zone 0,1, and 2 shall be connected by supplementary protective bonding conductors to the protective conductors of exposed-conductive-parts of equipment situated in these zones in accordance with regulation 415.2.All the requirements of Part 4 should be met as well as additional protection provided by:

702.522.22 — In zones 0 and 1, a wiring system shall be limited to that is necessary to supply the equipment in that zone.

•

Residual Current Devices for circuits in all zones and

•

Supplementary equipotential bonding.

702.414.4.5 — Basic protection shall be provided by either basic insulation complying with Regulation 416.1, or barriers or enclosures affording a degree of protection of at least IPXXB or IP2X. 702.512.2 — Electrical equipment shall have at least a degree of protection according to BS EN 60529. Zone 0

IPX8

Zone 1

IPX4, IPX5 where jets are likely to be used for cleaning purposes

Zone 2

IPX2 for indoor locations and

702.522.23 — For a fountain the following additional requirements are to be met. •

The cable for electrical equipment in zone 0 to be run in the shortest route practical.

•

In zone 1 the cable should have the protection of AG2 and the relevant submersion in water depth AD8.

702.522.24 — Junction boxes are not allowed in zones 0 and 1, but in SELV circuits this is permitted in zone 1 only. 702.53 — Switchgear and controlgear In zone 0 and 1 Switchgear and controlgear shall not be installed. In zone 0 and 1 a socket-outlet shall not be installed. In zone 2 a socket-outlet may be installed provided one of the following measures are applied: SELV, ADS or Electrical separation

IPX4 for outdoor locations IPX5 where jets are likely to be used for cleaning purposes 702.522.21 — In zones 0, 1 and 2 any metallic covering or


Page | 180

17th Edition Training Manual NOTE: For a swimming pool for where it is not possible to locate a switch or socket-outlet outside zone 1, a socketoutlet preferably having a non-conductive coverplate is permitted in zone 1. It must be located 1.25 m from the border of zone 0 and 0.3m above the floor level with the protection of either SELV, ADS or electrical separation.

removable by the use of a tool. Luminaires to be to BS EN 60598-2-18 and electric pumps to comply with BS EN 60335-2-41. 702.55.4 — Special requirements for the installation of electrical equipment in zone 1 of swimming pools and other basins. Fixed equipment designed for use in swimming pools and other basins (e.g. filtration systems, jet stream pumps) and supplied at low voltage is permitted in zone 1, subject to requirements being met. For swimming pools where there is no Zone 2 lighting equipment other than SELV may be installed on a wall or a ceiling provided. •

It is protected by a RCD to Regulation 415.1.1.

•

Mounted at a height a least 2m above the level of Zone 1.

Fig. 82 Socket with non-conductive plate can be installed in Zone 1 where not possible to install elsewhere

702.55.2 — Underwater Luminaires A luminaire for use in the water or in contact with the water shall be fixed and comply with BS EN 60598-2-18. 702.55.3 — Electrical equipment in fountains Equipment in zones 0 and 1 of a fountain will have a mechanical protection to AG2 e.g. glass or grids only


Fig. 83 Zones for fountains including air spray - see BS7671 Fig 702.4

Page | 181

17th Edition Training Manual Section 703 - Rooms & Cabins Containing Sauna Heaters

Zone 1 - The volume containing the sauna heater and the area of 0.5m from the surface of the heater. Zone 2 - The volume outside Zone 1 and rises to 1

Rooms and cabins containing sauna heaters are considered by BS7671 to be a location of increased electric shock risk, as large areas of the human body are exposed and are wet due to perspiration and occasional high humidity.

703.411.3.3 — Additional protection by RCDs

For those changing updating from 16 to 17 Edition, note that zones A, B & C in the 16th are now Zones 1, 2 and 3, and the related dimensions have been changed.

All circuits of the sauna will be protected by the use of one or more RCDs.The sauna heater need not be protected by a RCD unless recommended by manufacturer.

th

Fig. 84 Zone dimensions - sauna. Elevation


th

meter above the floor level. Zone 3 - The volume outside of Zones 1 and 2.

Fig. 85 Zone dimensions - sauna. Plan

Page | 182

17th Edition Training Manual 703.512.2 — External Influences All equipment shall have a degree of protection to at least IPX4. If cleaning is carried out using jets – to at least IPX5. Zone 1 Only the heater and directly associated equipment to be installed. Zone 2

No special requirements for heat resistance.

Zone 3

Equipment suitable for 125°C Cables 170°C.

All Switchgear, other than the thermostat and the thermal cut-out, to be installed outside the sauna. 703.52 — Wiring systems The wiring should be installed outside the zones, preferable outside the sauna. When this is unavoidable the wiring should be heat-resistant and metallic sheaths and metallic conduits shall not be accessible in normal use. 703.53 — Selection and erection of equipment; Isolation, switching, control and accessories 703.537.5 — Switchgear and controlgear, which form part of the sauna heater equipment of other fixed equipment installed in zone 2, may be installed within the sauna room in accordance to manufacturer’s instructions. Other switchgear and controlgear, e.g. lighting shall be placed outside the sauna room or cabin. Socket-outlets shall not be installed within a sauna room or cabin. 703.55 — Other equipment Sauna heating appliances shall comply with BS EN 60335-253


Fig. 86 Electric sauna heater

Page | 183

17th Edition Training Manual Section 704 - Construction and Demolition Sites Construction sites are considered to be a special location due to the increased risks associated with: •

Trailing cables

•

The use of portable electric tools

•

Many extraneous-conductive-parts that cannot, practically, be bonded

•

Adverse weather conditions and incomplete structures

•

Difficult working conditions

704.1 — Scope The buildings and installations that are covered by Section 704 are: •

Construction work on new buildings

•

Repair, alteration, extension, demolition of existing buildings or parts of buildings

•

Engineering works

•

Earthworks

•

Work of similar nature

704.410.3.10 — Circuits up to and including 32A supplying socket-outlets and hand-held equipment to be protected by: •

Reduced low voltage or

•

Automatic disconnection of supply with RCD protection to 415.1.1), Electrical separation, or SELV or PELV.

NOTE: Reduced low voltage is strongly preferred for portable hand lamps, portable tools and local lighting up to 2 kW. NOTE: SELV is preferred for portable hand lamps in confined spaces. 704.411 — Protective measures: ADS •

Construction site earthing systems will normally be TT.

•

TN-S may be used, particularly on larger sites in conjunction with TT systems.


Page | 184


TN-C-S is prohibited for supplies to construction sites (except fixed buildings on the site).

•

Current using equipment shall be supplied by ACSs comprising of:

Distributors may be reluctant to supply a TN-C-S

•

Overcurrent protective devices

system to some sites as the ESQCR prohibit its use.

•

Devices affording fault protection

•

Socket-outlets, if required

704.4113.2 — ADS in the case of a fault Circuits supplying one or more socket-outlets with a rated current exceeding 32A requires a RCD not exceeding 500 mA for protection. 704.414 — Reduced low voltage systems For portable hand-held tools and hand lamps and local lighting 110 V single-phase, centre point earthed or 110 V 3phase, star point earthed systems should be used. 704.511.1 — All assemblies for the moveable electrical distribution system shall comply with BS EN 60439-4. All cable couplers (Socket-outlets and plugs) must comply with BS EN 60309-2 704.52 — Wiring systems 704.522.8.10 — Care required to be taken to avoid cables being installed across a site road or walkway unless adequate mechanical protection has been provided. 704.537.2.2 — Devices for isolation Each Assembly for Construction Sites (ACS) shall incorporate suitable devices for isolation and switching of the incoming supply. Distribution equipment to BSEN 60439-4 to incorporate suitable devices for switching and isolation (lockable).


Fig. 87 Construction site electrical distribution equipment

Page | 185

17th Edition Training Manual Identification of different voltages on site

25V


>50V-250V DC

100-130V

200-250V

380-460V

50-60Hz

50-60Hz

50-60Hz

Page | 186

17th Edition Training Manual Section 705 - Agricultural & Horticultural Premises Increased shock risk due to: •

Reduced body resistance of humans resulting from the wet environment and nature of premises.

•

Animals susceptible to electric shock at lower levels.

•

Mechanical damage to wiring systems from machinery and animals.

•

Fire.

Fig. 88 Farm and farmyard


705.1 — Scope Section 705 applies to indoor and outdoor installations where livestock is kept (not to dwellings intended for human habitation) •

Stables, barns, chicken-houses, piggeries

•

Horticultural premises:

•

Garden centre, nurseries, greenhouses

•

Also locations carrying out the production, storage, preparation and processing of animal feeds, fertilizers and vegetable and animal products.

Fig. 89 Section 705 includes garden centres

Page | 187

17th Edition Training Manual 705.411.4 — Earthing systems A TN-C system earthing arrangement must not be used on these installations. This requirement applies also to residences and other locations belonging to agricultural and horticultural premises. 705.415.2.1 — Additional protection In locations intended for livestock, supplementary bonding shall be used to connect all exposed-conductive-parts and extraneous-conductive-parts that can be touched by livestock.

IPX4 either by construction or by supplementary / additional. 705.512.2 — External influences In agricultural or horticultural premises, electrical equipment will have a minimum IP rating of IP44, either by construction or by supplementary / additional. Socket-outlets must have the appropriate protection against the external influences that may apply. These requirements do not apply to any residential locations, office, shops belonging to the agricultural or horticultural premises.

705.422 — Measures for protection against fire

705.513 — Accessibility

705.422.6 — Heating appliances used for the breeding and rearing of livestock shall comply with BS EN 60335-2-7-1and be fixed as to maintain an appropriate distance from livestock and combustible materials to avoid the risk of burns to livestock or fire.

Electrical equipment must be inaccessible to livestock, where this is unavoidable it must be constructed and installed to avoid damage and minimize the risk of injury to livestock.

705.422.7 — For fire protection purposes a 300ma RCD must be installed, if there are no socket-outlets in the protected circuit a time-delayed or ‘S’ type can be used. When a circuit that protects socket-outlets is protected by a 30mA RCD to Regulation 411.1 it also fulfils the criteria for fire protection. 705.422.8 — In locations where there is a risk of fire exists any circuit supplied from an extra-low circuit (50v A.C./ 120v D.C.) must have a degree of protection to IPXXD or


705.514.9.3 — Diagrams and documentation The following documentation must be provided to the user •

A plan indicating the location all electrical equipment

•

The routing of all concealed cables

•

A single-line diagram of the distribution system

•

An equipotential bonding diagram indicating the locations of all bonding connections

Page | 188

17th Edition Training Manual 705.52 —Wiring systems

705.522.16 — Conduit/trunking systems

In locations accessible to livestock, the wiring system shall be erected to be inaccessible to the livestock or suitably protected against mechanical damage.

Where livestock is kept external influences classified to AF4 Conduit and protection against corrosion of Class 2 (medium) for indoor, Class 4 (high) for outdoors to BS EN 61386-21.

Cable selection and installation to take account of presence of rodents. Where vehicles and mobile machinery operate: •

Cables shall be buried 0.6m with mechanical protection.

•

Cables in cultivated land to be buried to at least 1m.

•

Cables used for overheads to be insulated and suspended at least 6 m high.

In locations where impact is deemed to be likely due to vehicles operating the equipment will be classified as AG3 and conduit will have a degree of protection 5J (impact) to BS EN 61386-21 and trunking and ducting systems will comply with BS EN 50085-2-1. 705.537.2 — Isolation The electrical installation in each building or part of a building shall be isolated by a single isolation device according to Chapter 53. The isolation devices shall be clearly marked according to the part of the installation to which they belong. Devices used for isolation and switching and devices used for emergency stopping or switching shall be erected so they are accessible to users and inaccessible to livestock. They will also be clearly marked and will break all live conductors.

Fig. 90 Pests such as rats and mice are a particular problem to protect against on agricultural locations


Page | 189

17th Edition Training Manual 705.560.6 — Automatic life support for high density livestock rearing Special consideration needs to be given where high density livestock rearing occurs.In these cases it is essential that supplies of food, water, air, ventilation, heating and/or lighting where required, are not compromised. Standby electrical supplies and automatic monitoring may be necessary.

Fig. 91 Indication of earth bonding connections in a milking parlour


Page | 190

17th Edition Training Manual Section 706 - Conducting Locations with Restricted Movement 706.1 — Scope This requirement of this section applies to: Fixed equipment in a conducting location or surroundings where movement of persons is physically constrained or restricted and these locations are conductive and in contact with the general mass of Earth. The supplies for the use of any electrical equipment or mobile equipment should be therefore, limited to only essential items. 706.41 — Protection against electric shock Hand-held tools or items of mobile equipment should be supplied by either: •

Electrical separation or

•

SELV

•

For supplies to hand lamps, only SELV systems

Requirements for fault protection For supplies to fixed equipment there are several options: •

Automatic disconnection of supply combined with supplementary bonding

•

Class II equipment supplemented by RCD

•

Electrical separation (supplying only one item of equipment being connected to the secondary winding of the isolating transformer),

•

SELV, or

•

PELV (with equipotential bonding).

706.411 — Automatic disconnection of supply Only circuits and protective measures stated in Regulation 706.410.3.10 are permitted. 706.411.1.2 — If a functional earth is required for certain equipment, all exposed-conductive-parts must be connected to any extraneous-conductive-parts. 706.413 — Electrical separation The unearthed source must be located outside the conducting location, unless it is part of the fixed installation within the conducting location. 706.414 — SELV and PELV The source for SELV and PELV must be located outside the conducting location, unless it is part of the fixed installation within the conducting location.

should be used


Page | 191

17th Edition Training Manual Section 708 - Electrical Installations in Caravan/Camping Parks and Similar Locations

TN-C-S can be used to supply permanent buildings on the site although consideration should be given where this includes buildings open to the public e.g. toilet blocks containing bath or showers and kitchen or washing facilities.

It is important that the differentiation between Section 708 electrical installations in caravan parks, camping parks and similar locations and 721 Electrical installations in caravans and motor caravans is fully understood.

708.512.2 — External influences Electrical equipment installed outside in a caravan park shall comply with. External Influence

IP Rating

Water splashes

AD4

IPX4

BSEN 60529

Ingress of objects

AE2

IP3X

BSEN 60529

Mechanical impact

AG3

IK08

BSEN 62262

Table 16 IP Rating for equipment installed outside on caravan park

708.521.1 — Wiring Systems – supplies to caravan pitches Either underground or overground distribution systems are suitable. 708.521.1.1 — Underground cables Maximum supply voltage of 230V single-phase or 400V three-phase applies. 708.411.4 — The Electricity Safety, Quality and Continuity Regulations 2002 prohibits distributors from offering connections to earthing terminals from PME networks.


Underground cables shall be buried to a depth of at least 600mm and have additional mechanical protection. If this is not possible, to be placed outside the zone of the caravan pitch away from where tent pegs or ground anchors are expected to be used.

Page | 192

17th Edition Training Manual 708.521.1.2 — Overhead cables •

All overhead conductors to be insulated.

•

Poles and other supports to be protected against damage by vehicle movement.

•

Overhead conductors to be at a height of no less than 6m in areas with vehicle movement and 3.5 in any other area.

accommodation vehicle (including caravans) or tent shall be protected individually by an overcurrent protective device, in accordance with the requirements of Chapter 43. 708.553.1.13 — Each socket-outlet to have its own RCD protection as specified in Regulation 415.11 708.533.1.14 — Socket outlet protective conductors shall not be connected to a PME earthing facility.

708.530.3 — Caravan pitch electrical supply equipment Supply equipment should be located adjacent to the pitch and not more than 20 m from the connection facility of caravan or tent when on its pitch. NOTE: Not more than four socket-outlets should be grouped in supply/board, to avoid the supply cable crossing a pitch other than the one intended to be supplied. 708.553.1.8 — Each socket-outlet will comply with BS EN 60309-2 and have an IP rating of IP44 708.553.1.9 — The socket-outlet will be mounted at a height of 0.5m to 1.5m from the ground, if there is a risk of flooding or heavy snowfall this maximum height is permitted to exceed 1.5m 708.553.1.10 — The current rating of each socket-outlet to be no less than 16A 708.553.1.11 — At least one socket –outlet for each caravan 708.553.1.12 — Each socket-outlet to have its own overcurrent protection. A fixed connection for supply to each leisure


Fig. 92 Electrical supply point (includes water supply in this instance). Note voltage of 200-250V indicated by colour of socket

Page | 193

17th Edition Training Manual Pitch socket-outlets and connection to an earth electrode.

Section 709 - Marinas and Similar Locations

TN-S systems can be used on caravan sites but TT systems are more common.The separation of the caravan pitch TT earthing arrangement from the distributor’s PME earthing terminal may be made at one of a number of places:

709.1 — Scope

Option 1: Separation of caravan pitch TT earthing arrangement from distributor’s PME earthing facility. At consumers distribution position.

Section 709 provides information relating to the additional requirements in relation to circuits intended to supply pleasure craft or houseboats in marinas and similar locations.

Option 2: Separation of caravan pitches TT earthing arrangement from distributor’s PME earthing facility At pitch supply position. Cord extension sets are used to connect the caravan pitch socket-outlet to the caravan.Fig 708 of BS 7671 provides the requirements, which includes: •

A plug as specified in BSEN 60309-2

•

Flexible cable to H05RN-F (BS 7919):

•

Maximum length 25 m

•

A current rating of 16 A (minimum) conductor csa to be 2.5 mm2

•

Colour identification in accordance with Table 51

•

A socket as specified in BSEN 60309-2.

Fig. 93 Chichester marina - local to the publishers of this course


Page | 194

17th Edition Training Manual There is increased risk of electric shock due to: •

Wet conditions

•

The environment can be very harsh (mechanical damage, corrosion, movement etc

•

Flammable liquids

•

Standardization of equipment issues

The normal voltage for the supply to pleasure craft or houseboats shall be 230V A.C. single-phase or 400V A.C. three-phase. 709.411.4 — In the UK the ESQR prohibit the connection of a PME earthing facility to any metalwork in a boat. TN-C-S may be used for fixed site buildings, for supplies other earthing arrangements to be considered i.e. TT systems would normally be used for boat supplies although there are other methods. Shore-side supplies to permanent buildings may be TN-C-S, TN-S or TT.

709.512.2 — External influence External Influence

IP Rating

Water splashes

AD4

IPX4

Water jets

AD5

IPX5

Water waves

AD6

IPX6

Ingress of objects

AE2

IP3X

Corrosive or polluting substances

AF2

If hydrocarbons present

AF3

Mechanical impact

AG3

IK08

Table 17 IP Rating for marinas

709.521 — Wiring systems for marinas Regulation 709.521 lists six wiring systems that are acceptable and four that aren’t (above a jetty, wharf, pier or pontoon). Acceptable wiring systems •

Underground cables.

•

Overhead cables or overhead insulated conductors.

•

Cables with copper conductors with thermoplastic insulation and sheath installed within a cable management system that has been considered


Page | 195

17th Edition Training Manual taking into account of any external influences such as Movement, Impact, Corrosion and Ambient temperature •

Mineral Insulated cables with PVC protective coating.

•

Cables with armoring and thermoplastic material.

•

Other cables and materials that are no-less than those listed above.

Not acceptable and not to be used above a jetty, wharf, pier or pontoon •

Cables in free air suspended from or incorporating a catenary wire

•

Non-sheathed cables in conduit or trunking

•

Cables with aluminium conductors

•

Mineral insulated cables

709.521.1.6 — Cables shall be selected and installed to prevent mechanical damage from movement of floating structures and allow for constant flexing, be able to resist corrosion and tolerate the presence of water. Cable management systems to have drainage holes 709.521.1.7 — Underground cables Underground cables to be buried to the minimum depth of 500mm if no additional protection is provided. 709.521.1.8 — Overhead cables

Poles and other supports to be protected against damage by vehicle movement. Overhead conductors to be at a height of no less than 6m in areas with vehicle movement and 3.5 in any other area. 709.531 — Fault protection by automatic disconnection of supply. Where automatic disconnection of supply is the protective measure, socket-outlets supplying pleasure craft and houseboats and all final circuits intended for fixed supplies to houseboats require: Socket-outlets to be protected by an RCD having the characteristics specified in 415.1.1. RCDs must also be of a type that disconnects all poles (including the neutral). 709.533 — Protection against overcurrent Each socket-outlet, shall be protected by an individual overcurrent device in accordance with Chapter 43. In the instance where a houseboat requires a fixed supply, it shall be protected by an individual overcurrent device in accordance with Chapter 43. 709.537 — Isolation and switching 709.537.2.1 — At least one means of isolation shall be installed in each distribution board. This switching device shall disconnect all live conductors. A requirement of this isolation device is that it should only supply a maximum of four socket-outlets.

All overhead conductors to be insulated.


Page | 196

17th Edition Training Manual 709.553.1 — Plugs and socket-outlets Requirements for marina socket-outlets. 709.533.1.8 — Socket-outlets to comply with BS EN 60309-2 up to 63A and BS EN 60309-1 above 63A. Every socket-outlet to meet with the degree of protection to IP44. If the external influence increase to AD5 or AD6 the degree of protection required will be IPX5 or IPX6 respectively.

All feeder pillar and distribution board doors should be fitted with locks to prevent unauthorized access and have intermediate barriers to protect against accidental contact with live parts when the doors are open. The barriers should provide a degree of protection of at least IP2X or IPXXB. Fig 709.3 in the Regulations details a sample electrical information notice for marina users.

709.533.1.9 — Each socket-outlet will be located within proximity to the berth to be supplied. 709.533.1.10 — No more than 4 sockets at any one point. 709.533.1.11 — The maximum number required for each craft is 1 per craft or houseboat. 709.533.1.12 — In general the rating will be 16A at 200-250V. 709.533.1.13 — The mounting height of socket-outlets will be no less than 1m above the highest water level. On floating pontoons and walkways, this can be reduced to 300mm provided appropriate measures are taken to protect against water splashing. Where the particular feeder pillars are in external locations they should be constructed of glass reinforced plastic (GRP), or have GRP housings. GRP is preferred to galvanized steel for protection against corrosion in such environments. In order to counteract condensation within feeder pillar enclosures, low wattage ‘anti-condensation’ heaters should be installed.


Fig. 94 Marina pedestal for the supply of electricity (and water)

Page | 197

17th Edition Training Manual Section 710 - Medical Locations This is a new section added in Amendment 1 of BS7671 and then fully replaced in June 2013 with the Corrigendum 710.1 — Scope Section 710 applies to electrical installations in medical locations to ensure the safety of patients and medical staff. These requirements, in the main, refer to hospitals, private clinics, medical and dental practices, healthcare centres and dedicated medical rooms in the workplace, they can also be used in veterinary clinics and applies to locations designed for medical research.

The requirements of this section do not apply to medical electrical (ME) equipment. 710.3 - Assessment of general characteristics Each medical location shall have its own classification and group number which shall be determined by the type of medical procedures that will take place within the location. This makes it necessary for the relevant medical staff to indicate which medical procedures will take place within the location. (Annex 710 on Page 238 of BS7671 provides examples for the allocation of group numbers and classification for safety services of medical locations) Where a medical location may be used for different medical procedures the requirements of the higher Group classification should be applied 710.312.2 – Types of system earthing PEN conductors shall not be used in medical locations and medical buildings downstream of the main distribution board. 710.313.1 - The distribution system for medical locations shall be designed and installed to facilitate the automatic changeover from the main distribution network to the electrical safety source feeding essential loads, as required by Regulation 560.5.

Fig. 95 Hospital theatre room, but note, the specialist medical equipment is not part of BS7671


710.411.3.2.1 - Automatic disconnection in the case of a fault 710.411.3.2.1 - In medical locations of Group 1 and Group 2, where RCDs are required, only type A according to BS EN

Page | 198

17th Edition Training Manual 61008 and BS EN 61009 or type B according to IEC 62423 shall be selected, depending on the possible fault current arising. Type AC RCDs shall not be used. 710.411.3.2.5 - In medical locations of Group 1 and Group 2, the following shall apply: •

For TN, TT and IT systems, the voltage presented between simultaneously accessible exposedconductive-parts and/or extraneous-conductiveparts shall not exceed 25 V a.c. or 60 V d.c.

•

For TN and TT systems, the requirements of Table 710 shall apply.

Make a mental note of the location of Table 710 on page 231 of BS7671 as there is a likelihood of a question appearing in the exam relating to thie values contained within this table. 710.411.3.3 - An RCD shall not be used as a means of additional protection for a medical IT system. 710.411.4 - TN system In final circuits of Group 1 rated up to 63A, RCDs with a rated residual operating current not exceeding 30 mA and an operating time not exceeding 40 ms shall be used. (See regulation 415.1.1 for full characteristics of RCD). In Group 2 medical locations (excluding IT), RCDs complying with Regulation 415.1.1 can only be used on the following circuits: •

Circuits for the supply of movements of fixed


operating tables, or •

Circuits for X-ray units, or

•

Circuits for large equipment with a rated power greater than 5 kVA.

710.411.5 - TT system In Group 1 and Group 2 medical locations, RCDs shall be used as disconnection devices. 710.411.6 - IT system An IT system shall be used for final circuits supplying medical electrical equipment and life support systems, surgical applications and other electrical equipment located or that may be moved into the ‘patient environment’ in Group 2 medical locations. Equipment listed in Regulation 710.411.4 is excluded. At least one IT system is necessary for each group of rooms serving the same function and the IT system shall be equipped with an IMD (insulation monitoring device) in accordance with BS EN 61557-8. Note the additional specific requirements required by Regulation 710.411.6.3.1 710.411.7 - Functional extra-low voltage (FELV) is not permitted as a method of protection against electric shock in medical locations. 710.415.2 - Additional protection: Supplementary equipotential bonding Supplementary equipotential bonding shall be installed in medical locations of Group 1 and 2. The supplementary

Page | 199

17th Edition Training Manual bonding conductors shall be connected to the equipotential bonding busbar for the purpose of equalizing potential differences between the following parts. These are parts that may be located or moved into the ‘patient environment’. •

Protective conductors

•

Extraneous-conductive-parts

•

Screening against electrical interference fields

•

Connection to conductive floor grids

•

Metal screens of isolating transformers

Supplementary equipotential bonding connection points for the connection of ME equipment shall be provided in each medical location, as follows: Group 1: a minimum of one per patient location Group 2: a minimum of four but not less than 25% of the number of medical IT socket-outlets provided per patient location 710.415.2.2 - In Group 1 and Group 2 medical locations, the resistance of protective conductors, including the resistance of the connections, between the protective conductor of socket outlets and of fixed equipment or any extraneousconductive-parts and the equipotential busbar shall not exceed 0.7Ω and 0.2Ω respectively. 710.415.2.3 - The equipotential bonding busbar shall be located in or near the medical location. Connections shall be arranged so that they are accessible, labelled and clearly visible and can easily be disconnected individually. 710.512.1.1 - Transformers for IT systems shall be in


accordance with BS EN 61558-2-15 and installed in close proximity to the medical location. There are also additional requirements for transformers for IT systems at these locations which are covered by Regulation 710.512.1.1 710.512.1.2 - In the event of a first fault to earth, a total loss of supply in Group 2 locations shall be prevented. 710.512.2.1 - Socket outlets, switches and electrical devices shall be installed at least 0.2 m from medical gas outlets in order to minimize the risk of ignition of flammable gases. 710.537 - Isolation and switching Automatic changeover devices shall be arranged so that safe operation between supply lines is maintained. Automatic changeover devices shall comply with BS EN 60947-6-1 710.553.1 - Socket outlet circuits in the medical IT system for medical locations of Group 2 Socket-outlets intended to supply medical equipment shall be unswitched. At each patients place of treatment e.g. bedheads, the configuration of socket-outlets shall be as follows: •

each socket-outlet supplied by an individually protected circuit, or

•

several socket-outlets separately supplied by a minimum of two circuits

Socket-outlets used on medical IT systems shall be coloured blue and clearly and permanently marked ‘Medical

Page | 200

17th Edition Training Manual Equipment Only’.

Changeover period less than or equal to 0.5 s

710.559 - In Group 1 and Group 2 medical locations at least two different sources of supply shall be provided for luminaires and lighting installations, one of which shall be connected to the supply system for safety services.

In this case, a safety power supply source that is capable of providing power for at least 3 hours to essential lighting such as operating theatre tables, light sources in medical equipment such as endoscopes and monitors and life supporting medical equipment, shall be used.

710.56 - In medical locations, a power supply for safety services is required. The safety power supply shall automatically take over if the voltage of one or more incoming live conductors of the main distribution board of the building with the main power supply has dropped for more than 0.5 s and more than 10%. Refer to Annex A710 of BS 7671 for a list of examples. 710.560.5.5 - General requirements for safety power supply sources of Group 1 and Group 2 Primary cells are not allowed as safety sources An additional main incoming power supply, from the general power supply, is not regarded as a source of the safety power supply. The availability (readiness for service) of safety power sources shall be monitored and indicated at a suitable location. Regulations 710.560.6.1.1 to 710.560.6.1.3 provide detailed requirements for safety power supply services. Depending on the medical equipment concerned and to some extent, how critical that equipment is to the health of the patient, various changeover periods and durations of secondary power are defined.


The normal power supply shall be restored within a changeover period not exceeding 0.5 s. Changeover period less than or equal to 15 s In this case, a safety power supply source that is capable of providing power for at least 24 hours to equipment meeting the requirements of Regulations 710.560.6.1.1 and 710.560.6.1.2 shall be used. In the event of the voltage of one or more live conductors at the main distribution board for the safety services decreasing by more than 10% of the nominal supply voltage and for a duration of greater than 3 s, then the equipment shall be connected to the safety power supply source within 15 s. Changeover period greater than 15 s This is for less critical equipment required for the maintenance of hospital services and not covered by Regulations 710.560.6.1.1 and 710.560.6.1.2. In this case, a safety power supply source that is capable of providing power for at least 24 hours and which can be connected either automatically or manually shall be used.

Page | 201

17th Edition Training Manual 710.560.9.1 - Safety lighting

safety source power supply in Group 1 medical

In the event of mains power failure, the changeover period to the safety power source shall not exceed 15 s. The necessary minimum illuminance shall be provided for:

location rooms.

•

Emergency lighting and exit signs to BS 5266.

•

Locations for switchgear and controlgear for

safety services power source.

boards of the normal and safety services power

710.560.11 - Other services

At least one luminaire in rooms in which essential safety services power source. Locations of central fire alarm and monitoring systems.

•

medical location rooms shall be supplied from the The luminaires of escape routes shall be arranged on alternate circuits.

services are intended, shall be supplied from the •

A minimum of 90% of the lighting in Group 2

emergency generating sets, for main distribution supplies. •

•

At least one luminaire shall be supplied from the

This regulation lists examples of other services that may require a safety service supply with a changeover period not exceeding 15s. The list is not exhaustive and includes examples such as firefighter’s lifts, smoke extractors, paging systems, medical equipment and fire detection and extinguishing systems. Fig 710.1 and 710.2 provide diagrams of typical patient environment and operating theatre layout.

Fig. 96 Illustration of patient environment. See BS7671 Figs 710.1 and 710.2 for full details


Page | 202

17th Edition Training Manual Section 711 - Exhibitions, Shows and Stands 711.1 — Scope Temporary electrical installations in exhibitions, shows and stands are specified as a special location due to the:

Section 711.1 does not apply to the electrical systems as defined in BS 7909 for: •

Structures

•

Sets

•

Temporary nature of the installation

Mobile units as used in public or private events

•

•

•

Lack of permanent structures

Touring shows

•

•

Severe mechanical stresses

Theatrical, radio

•

•

Increased risk of fire and burns

TV or film productions and similar activities of the

•

Access to these installations by the general public

Typical examples of such installations include:

entertainment industry 711.313 — Supplies

•

Exhibitions

The nominal supply voltage for a temporary electrical installation shall not exceed 230/400V A.C. or 500V D.C.

•

Trade fairs

•

Outdoor shows

711.32 — External influences

•

Temporary entertainment venues

•

Kiosks

•

Outdoors fast food outlets

Any external influence that may be present or anticipated must be taken into account e.g. water, mechanical stress/damage. 711.410.3.4 — The cable intended to supply temporary structures shall be protected at its origin by a RCD rated not to exceed 300mA. A device to BS EN 60947-2(time delay) or BS EN 61008-1 or BS EN 61009-1(S-Type) can be used provided there is an RCD protecting the final circuits. 711.411.3.1.2 — Protective equipotential bonding Because of the practical difficulties ensuring main equipotential bonding to all extraneous-conductive-parts, structural metallic parts shall be connected through the main protective bonding conductors to the main earthing terminal within the unit.


Page | 203

17th Edition Training Manual 711.411.3.3 — RCD protection requirements

711.42 — Protection against thermal effects

Type of Circuit

Maximum Rated Residual

711.422.4.2 — Heat generation

Current l Δn

Equipment that generates heat to be suitably guarded and installed as not to cause danger.

At the origin of a cable intended to supply a temporary structure

300 mA RCD incorporating time delay to provide discrimination with final circuit RCDs (BS EN 60947-2 or S-type to BS EN 61008-1 or BS EN 610091)

Additionally, where the protective measure is automatic disconnection of supply Each socket-outlet circuit rated current up to 32 A

30 mA

All final circuits (other than those supplying emergency lighting)

30 mA

Table 18 RCD protection requirements

Particular attention should be given to the choice and location of lighting equipment. The construction material of showcases and signs should have adequate heat resistance, mechanical strength, ventilation and electrical insulation. 711.51 — Switchgear and controlgear to be in locked cabinet which can only be opened by the use of a tool or key. 711.52 — Wiring systems Armored Cables or cables to be mechanically protected i.e. conduit. The minimum csa of the wiring cables to be 1.5mm2. Flexible cords shall not be laid in areas accessible to the public unless they are protected against mechanical damage. 711.521 — If no fire alarm system installed in the building that the temporary installation is erected:

711.411.4 — TN System

•

Flame retardant cable to be used.

Only TN-S systems to be used for suppliesTN-C and TN-C-S systems are prohibited by BS 7671.TN-S supplies are acceptable provided accessible metallic parts to have protective equipotential bonding.

•

Single core or multi core unarmored cables enclosed in either metallic or non-metallic trunking or conduit to BS EN 61386 orBS EN 50085providing a degree of protection to IP4X.

In most cases TT systems will be the norm, especially outdoors.Indoor systems will vary.


Page | 204

17th Edition Training Manual 711.526.1 — Electrical connection Joints to be avoided where possible except where necessary as a connection into a circuit. Where these joints are made they shall be in accordance with the relevant standards or within an enclosure to IP4X or IPXXD. 711.537.2.3— Every separate temporary structure, vehicle stand or unit shall be provided with its own means of isolation, which is readily accessible and properly identifiable. 711.55.7 — Sockets Adequate number of socket-outlets for safety reasons and, if floor mounted be protected against the ingress of water and withstand the anticipated walking traffic. 711.559 — Luminaires and lighting

guarded to prevent risk of injury to persons or ignition of materials711.6 — Inspection and Testing All temporary electrical installations of exhibitions, shows and stands are required to be inspected and tested in line with Chapter 61 after each assembly on site.

Section 712 - Solar Photovoltaic (PV) Power Supply Systems 712.1 — Scope Section 712 specifies the requirements for solar photovoltaic (PV) power supply systems. It also outlines the requirements for solar photovoltaic (PV) power supply systems operating in parallel with public low voltage distribution networks.

711.559.4.2 — Extra-low voltage systems to comply with BS EN 60598-2-23. 711.559.4.3 — Insulation piercing lampholders for festoon lighting to be compatible with cable and non-removable. 711.559.4.4.1 — Any sign or lamp to be fixed out of arm’s reach or protected against the risk of injury to persons. 711.559.4.4.2 — Luminaires to be fixed onto a noncombustible surface. 711.559.4.4.3 — An emergency switch that is easily visible, accessible and clearly marked to control any circuit supplying signs, lamps or exhibits. 711.559.5 — Thermal effect Luminaires below 2.5m (arm’s reach) to be firmly fixed and © 2008-2015 Electacourse

Fig. 97 PV equipment on roof

Page | 205

17th Edition Training Manual 712.410.3 — PV equipment on the D.C. side considered to be energised at all times. 712.411.3.2.1.1 — The PV supply cable shall be connected to the supply side of the protective device for automatic disconnection. 712.411.3.2.1.2 — Where ADS is the protective measure on the a.c. side, RCD protection may be required. The preferred protective measures on the d.c. side is Class II or equivalent insulation. 712.412 — Protection by Class II preferred for d.c. side 712.434.1 — PV cables protected against short-circuit currents by appropriate device.

to be carried out. 712.552.8.1 — PV cables shall be installed to prevent any risk of earth faults or short-circuits. 712.522.8.3 — Equipment & wiring systems selected for external influences i.e. wind, ice etc. 712.537.2.1.1 — To allow maintenance of the PV converter a means of isolation from both the a.c. and d.c. side to be provided.712.537.2.2.5 — Switch disconnectors to be supplied for d.c. side ( PV converter). 712.537.2.2.5.1 — Suitable warning notices fitted indicating that parts of the PV installation may still be live after isolation from the PV converter.

712.444.4.4 — Protection against EMI in buildings Wiring loops short (lightning strikes). 712.511.1 — Crystalline PV modules shall comply with the requirements of BS EN 61215. Class II modules are recommended if Uoc STC exceeds 120V d.c. 712.512 — PV strings may be connected in series depending on the voltage capabilities of the PV modules or the PV converter. The installation of PV modules should be installed so that the heat dissipation does not impose a risk. 712.513.1 — Accessibility The selection and erection of the PV equipment shall be installed to facilitate the safe maintenance and service work


Fig. 98 PV Array warning notice

Page | 206

17th Edition Training Manual 712.54 — Where protective conductors are installed they will be in parallel to and in close proximity with the cables and accessories. Further information should be sought prior to design or installation: •

Section 714 – Outdoor lighting installations This section applies to outdoor lighting installations comprising one or more luminaires, a wiring system and accessories, and to highway power supplies and street furniture.

Electrical Safety, quality and Continuity Regulations 2002 (ESQCR).

•

Energy Networks Association’s Engineering Recommendation G83/1.

•

Engineering Recommendation G59/1 (for installations over 16A).

•

Electrical Safety Council’s Best Practice Guide — Connecting a microgeneration system to a domestic or similar installation.

Fig. 99 Bus shelters included in new regulation Special Locations 714

The following are included: i.

Lighting installations such as those for roads, parks, car parks, gardens, places open to the public, sporting areas, illumination of monuments and floodlighting

ii.

Other lighting arrangements in places such as telephone kiosks, bus shelters, advertising panels


Page | 207

17th Edition Training Manual and town plans iii.

Road signs.

The following are excluded: i.

Temporary festoon lighting

ii.

Luminaires fixed to the outside of a building and supplied directly from the internal wiring of that building

iii.

Road traffic signal systems.

New regulation - 714. Isolation and switching 714.537.2 Isolation

Section 715 Extra-low voltage lighting installations Protection against overcurrent 715.430.104

Protection against overcurrent in ELV lighting installations The use of self-resetting overcurrent protective devices is permitted only for transformers up to 50 VA.

715.5 - Selection and erection of equipment 715.52 Wiring systems i)

Insulated conductors in conduit systems according to

714.537.2.1 General

BS EN 61386 series or cable trunking/ducting systems

714.537.2.1.1

according to BS EN 50085 series

Every circuit shall be capable of being isolated individually from each of the live supply conductors, except as detailed in Regulation 537.1.2. 714.537.2.1.201 Where it is intended that isolation and switching is carried out only by instructed persons and subject to suitable provisions being made so that precautions can be taken to prevent any equipment from being inadvertently or unintentionally energized, for TN systems, the means of switching the supply on load and the means of isolation is permitted to be provided by a suitably rated fuse carrier.

ii) Rigid cables iii) Flexible cables iv) Systems for ELV lighting according to BS EN 60598-2-23 v) Track systems according to BS EN 60570 vi) Bare conductors (see Regulation 715.521.106). Where parts of the ELV lighting installation are accessible, the requirements of Section 423 also apply. Metallic structural parts of buildings, for example pipe systems, or parts of furniture, shall not be used as live conductors.

714.537.2.1.202 Where the distributor's cut-out is used as the means of isolation of a highway power supply the approval of the distributor shall be obtained.


Page | 208

17th Edition Training Manual 715.521.106 Bare conductors If the nominal voltage does not exceed 25 V a.c. or 60 V d.c., bare conductors may be used providing that the extra-low voltage lighting installation complies with all the following requirements: i)

The lighting installation shall be designed, and installed or enclosed in such a way that the risk of a short-circuit is reduced to a minimum

ii) The conductors used shall have a cross-sectional area according to Regulation 715.524 iii) The conductors shall not be placed directly on combustible material. For suspended bare conductors, at least one conductor and its terminals shall be insulated for that part of the circuit between the transformer and the short-circuit protective device to prevent a short-circuit. 715.521.107 Suspended systems Suspension devices for extra-low voltage luminaires, including supporting conductors, shall be capable of carrying five times the mass of the luminaires (including their lamps) intended to be supported, but not less than 5 kg. Terminations and connections of conductors shall be made by screw terminals or screwless clamping devices complying with BS EN 60998-2-1 or BS EN 60998-2-2. Safety of the installation due to expected stresses in the conductors shall be in accordance with Regulation 559.5.2.


Insulation piercing connectors and termination wires which rely on counterweights hung over suspended conductors to maintain the electrical connection shall not be used. The suspended system shall be fixed to walls or ceilings by insulated distance cleats and shall be continuously accessible throughout the route. 715.524.201 The minimum cross-sectional area of the extralow voltage conductors shall be: i)

1.5 mm2 copper, but in the case of flexible cables with a maximum length of 3 m a cross-sectional area of 1 mm 2 copper may be used

ii) 4 mm2 copper in the case of suspended flexible cables or insulated conductors, for mechanical reasons iii) 4 mm2 copper in the case of composite cables consisting of braided tinned copper outer sheath, having a material of high tensile strength inner core. In ELV lighting installations, if the voltage drop between the transformer and the furthest luminaire does not exceed 5 % of the nominal voltage of the ELV installation it shall be deemed to comply with Section 525. Protective devices may be located above false ceilings, which are removable or easily accessible, provided that information is given about the presence and location of such devices. If the identification of a protective device for a circuit is not immediately evident, a sign or diagram (label) close to the protective device shall identify the circuit and its purpose.

Page | 209

17th Edition Training Manual SELV sources, protective devices or similar equipment mounted above false ceilings or in a similar place shall be permanently connected. SELV sources and their protective devices shall be installed so as to: i)

avoid mechanical stress on their electrical connections, and

ii) be adequately supported, and iii) avoid overheating of the equipment due to thermal insulation. 715.537.1.1 Where transformers are operated in parallel, the primary circuits shall be permanently connected to a common isolating device.

Section 717 - Mobile or Transportable Units 717.1 — Scope Applies to mobile vehicles & transportable containers/cabins. These types of units are designated as a special location because: •

The temporary nature of the installation

•

Risks associated with repeated connection and disconnection

•

Risks associated with different connection facilities

•

Difficulties establishing an equipotential zone

•

Vibrations problems


Fig. 100 Mobile medical unit

Units can be either: •

Mobile (vehicles, self-propelled or towed)

•

Transportable (containers, cabins etc)

These units will be pre-wired and require a suitable supply and connection. Typical industries employing these units are: entertainments, medical, advertising, fire-fighting, industry, commerce and catering. Section 717 does NOT apply to generating sets, marinas and boats, caravans, vehicle electrics.

Page | 210

17th Edition Training Manual 717.313 - Supplies Added in Amendment 1, one or more of the following methods shall be used to supply a unit: i.

Connection to a low voltage generating set, located

712.411.4 — PME earthing facility shall not be used.

inside the unit, in accordance with Section 551 (see

Unless these installations are under continuous supervision by a skilled or instructed person and the effectiveness of the means of earth has been confirmed prior to connection, TNC-S systems are prohibited.

Figure 717.1 of the Regs) ii.

Connection to a low voltage electrical supply external to the unit, in which the protective measures are effective (see Figure 717.3 of the Regs), the supply derived from either a fixed electrical installation or a generating set in accordance with Section 551

iii.

through the main protective bonding conductors to the main earthing terminal within the unit. The main protective bonding conductors shall be finely stranded.

717.415.1— RCD protection is required for every socketoutlet intended to supply current-using equipment outside the unit (unless SELV, etc).

Connection to a low voltage electrical supply external to the unit, and where internal protective measures are provided by the use of simple separation, in accordance with Section 413(see Figures 717.4, 717.5, (see Figures 717.4, 717.5, 717.6 and 717.7 of the Regs showing alternative forms of fault protection within the unit).

717.411.1 — Protective measures against electric shock ADS Automatic disconnection of supply. For a supply in accordance with 717.313(ii), Automatic disconnection of supply shall be provided by means of a residual current protective device, with a rated residual operating current not exceeding 30 mA. 717.411.3.1.2 — Accessible conductive parts of the unit, such as the conductive structure of the unit, shall be connected


Fig. 101 Outside equipment

Page | 211

17th Edition Training Manual 717.514 — Notices shall be available near the incoming supply to state the characteristics of:

i.

Plugs shall have an enclosure of insulating material

ii.

Connecting devices, plugs and socket-outlets, with

The type of supply which may be connected to the

an enclosure as necessary, shall afford a degree of

unit

protection of at leastIP44 when in use or connected

•

The voltage rating of the unit

and protection of at least IP55 when not connected,

•

The number of phases and their configurations

e.g. when the unit is in transit

•

The on-board earthing arrangement

•

The maximum power requirements of the unit

•

717.52 — Wiring systems H07RN-F (BS EN 50525-2-21) or equivalent, flexible cable, made of copper, have a minimum csa of 2.5mm2 and enter the unit by an insulating inlet 717.528.3.4 — Proximity of non-electrical services. No electrical equipment or wiring to run through gas cylinder storage areas except ELV controls. Where cables have to run through such a compartment, they shall be protected against mechanical damage by installation within a conduit or ducting system complying with relevant parts of BS EN 61386 and BS EN 50085 respectively. 717.55.1

The inlet (with “male” contacts) shall be situated on the unit.

Section 721 - Electrical Installations in Caravans and Motor Caravans Caravans are installations of increased electric shock risk because: •

Persons may be minimally clothed or exposed to wetness and, when outside, in contact directly with Earth.

•

Frequent road movement and the associated risk of vibration.

•

Potential problems relating to frequent connection and disconnection of supplies.

References to caravans also apply to motor-caravans.

Where the means of connection is a plug and socket-outlet, mounted, accessed or used outside the unit and used to connect the unit to the supply, or supply other equipment, it shall comply with the appropriate parts of BS EN 603092series and shall meet with the following requirements:


Page | 212

17th Edition Training Manual apply), or transportable units (Section 717 applies). 721.313.1.2 — Supplies The nominal supply voltage shall be 230 Vsinge phase or 400 V three phase a.c. The d.c. voltage should not exceed 48 V. 721.41 — Protection against electric shock 721.410.3.3.1 — Any portion of the installation operating at extra-low voltage will comply with Section 414 of BS 7671:2008. These power sources generally used operate at 12 V, 24 V and 48 V. d.c.

Fig. 102 Caravan interior

Caravan parks are covered in Section 708, and transportable units are covered in Section 717. 721.1 — Scope This particular requirement applies to the electrical installation of touring caravans and motor caravans with nominal voltages of 230Va.c or 48Vd.c. for circuits and equipment for use of the caravan for habitation purposes. Exclusions from scope •

Electrical circuits and equipment for automotive purposes.

•

Electrical installations of mobile homes and residential park homes (general requirements


In particular circumstances the voltage of 42 V rms is utilized. The protective measures of obstacles, placing out of reach, non-conduction location, earth-free equipotential bonding and electrical separation are not permitted except for the installation of shaver socket outlets. 721.411 — Protective measure : Automatic disconnection of supply. Where automatic disconnection of supply is used, a 30 mA RCD is required, which must interrupt all live conductors (Line and Neutral). This will normally be in place of the main incoming switch of the consumer unit of the caravan. The wiring system must include a CPC

Page | 213

17th Edition Training Manual connected to: •

The protective contact of the inlet, and

•

The exposed-conductive-parts of the electrical equipment (such as the metallic enclosure of Class I items of equipment), and

•

The protective contacts of the socket-outlets.

721.411.3.1.2 — Protective equipotential bonding Structural metallic parts accessible from within the caravan (such as the chassis) is required to be bonded to main earthing terminal of the caravan. 721.43 — Devices for protection against overcurrent. Each final circuit must be protected by an overcurrent protective device that disconnects all live conductors (line and neutral). NOTE: This means double-pole circuit-breakers are to be used for single-phase circuits. 721.514.1 — Identification Instructions shall be provided and will include: A description of the installation. A description of the function of the RCDs and use of the test button. A description of the function of the main isolating switch. The text of the instructions in Fig 721 must be displayed.


721.522 — External influences 721.522.7.1 — Vibration All cables that pass through metalwork or supported on rigid surfaces, will be protected against damage due to the likelihood of vibration. 721.522.8 — Mechanical stresses All cables and cables in rigid conduit to be supported at intervals not exceeding 400mm vertically and 250mm horizontally. (Onsite Guide Table 4A page 113.) 721.524.1 — All cable conductors to be no less than 1.5mm2 721.528.3.4 — Proximity of non-electrical services No electrical equipment or wiring to run through gas cylinder storage areas except ELV controls. Where they run through this area, they shall be protected against mechanical damage by installation in conduit to BS EN 61386 which has an impact equivalent toAG3. 721.537.2.1.1 — Isolation Each installation in a caravan will be provided with a main disconnector, which shall disconnect all live conductors (Line and Neutral) and positioned in a suitable accessible position. 721.537.2.1.1.1 — A notice of durable material to be permanently fixed near the main isolating device inside the caravan as shown in Fig 721. 721.543.2.3 — Protective conductors All protective conductors shall be incorporated in a multicore cable or in a conduit together with the Live

Page | 214

17th Edition Training Manual conductors. 721.55.1.1 — Inlets Any A.C. electrical inlet on the caravan shall be compliant with BS EN 60309-1 and only interchangeable with a BS EN 60309-2 socket. 721.55.1.2 — The inlet shall be installed

installed, provision is to be made for the securement when the caravan is in motion. 721.55.2.6 — The means of connection to the caravan pitch socket-outlet shall be supplied with the caravan and shall comprise of: •

A plug as specified in BSEN 60309-2.

•

At a maximum height of 1.8 m from ground level

•

Flexible cable to H05RN-F (BS 7919):

•

In a readily accessible position on outside of

•

Maximum length 25 m

caravan,

•

A current rating of 16 A (minimum) conductor

•

Have a minimum degree of protection of IP44

•

Must not protrude significantly beyond the caravan body

CSA to be 2.5 mm2 Colour identification in accordance with Table 51 and as covered earlier

A 16 A single-phase inlet is adequate for most caravans; to comply with BS EN 60309-2 with key position 6h, and be coloured blue.Higher rating connections to comply with BS EN 60309-2, if needed. 721.55.2 — Accessories 721.55.2.1 — Every low voltage socket-outlet other than one supplied from an isolating transformer shall incorporate an earth pin. 721.55.2.2 — Every socket-outlet shall have its voltage marked. 721.55.2.3 — Every accessory in a location which is exposed to moisture will be protected to IP44. 721.55.2.4 — Every luminaire shall be fixed directly to the structure of the caravan. In the case where a pendant is


Page | 215

17th Edition Training Manual Section 722 – Electric Vehicle Charging 722.1 Scope The particular requirements of this section apply to: i.

circuits intended to supply electric vehicles for charging purposes

ii.

protection for safety when feeding back electricity from an electric vehicle into a private or public supply network (under consideration).

722.410 - Protective measures of obstacle and placing out of reach and earth-free local equipotential bonding are not permitted 722.411 - A PME earthing facility shall only be used in particular installations: i.

installation is not likely to exceed 70V ii.

Where the installation is connected to an earth electrode, the rms voltage between the main earthing

Inductive charging is not covered. Electrical installations for charging mobility scooters and similar vehicles of 10 A and less are not covered.

An open-circuit fault of the network supplying the

terminal and Earth does not exceed 70V iii.

Protection is provided by a device which disconnects within 5s in the event of a the voltage between the protective conductor and Earth exceeding 70V

These regulations do not apply in the case of a charging point located at a dwelling. A dwelling is defined as a selfcontained unit to accommodate a single household. 722.512 - IP44 protection against water 722.531 - Each charging point to be protected by RCDs 722.55.201 - Detailed requirements relating to permitted sockets and connectors Fig. 103 Electric vehicle charging is becoming an important of the electrical installation infrastructure

722.311 - A dedicated final circuit shall be provided for the connection to electric vehicles 722.312 - For a TN system, the final circuit shall not include a PEN conductor


722.55.101.3 - One socket-one vehicle 722.55.101.5 - Socket height shall be between 05.m and 1.5m from the ground. Requirements of National Building Regulations need to be adhered to

Page | 216

17th Edition Training Manual Section 729 - Operating and Maintenance Gangways Another new section added in Amendment 1, applying to basic protection and other aspects relating to the operation or maintenance of switchgear and control gear within areas including gangways, where access is restricted to skilled or instructed persons.

evacuation. Clear signage warning of restricted access is therefore paramount. 729.513.2 - The width of gangways and access areas shall be adequate for work, transportation of equipment and emergency evacuation. Equipment doors and hinged panel must have space to open to at least 90 degrees. 729.513.2.1 - Restricted access areas where basic protection is provided by barriers or enclosures (refer to Fig 729.1 BS7671) Gangway width between: •

Barriers or enclosures and switch handles or circuit breakers and the wall - 700mm

•

Barriers or enclosures or other barriers or enclosures - 700mm

•

Height of gangway to barrier or enclosure above floor - 2000mm

•

Live parts placed out of reach - 2500mm

729.513.2.1 - Restricted access areas where protective measures of obstacles is applied (refer to Fig 729.2 BS7671)Gangway width between: Fig. 104 Passenger boarding bridge - a gangway

729.3 - Assessment of general characteristics

Restricted areas shall be clearly marked by appropriate signage and shall not provide access to unauthorized users. However, access doors to restricted areas shall be easily opened without a key or tool in order to allow for easy


•

Obstacles and switch handles or circuit breakers and the wall - 700mm

•

Obstacles or other obstacles and the wall - 700mm

•

Height of gangway to obstacles, barrier or enclosure above floor - 2000mm

•

Live parts placed out of reach - 2500mm

Page | 217

17th Edition Training Manual 729.513.2.3 - Access of gangways Gangways longer than 10m shall be accessible from both ends. Closed restricted access areas longer than 20m shall be accessible by doors from both ends. Fig 729.3 (a), (b) and (c) provides examples of positioning of doors in closed restricted access areas and require that doors giving access to gangways shall open outwards and be 700mm wide and 2000mm high as a minimum. Annex A729 provides ‘normative’ information for closed restricted access areas and illustrates how handles should be fitted, access doors should be hung and minimum passing width in the case of evacuation. Doors should close in the direction of the evacuation route. Where doors can be fixed in the open position and circuit breakers are withdrawn fully for maintenance, a minimum passing width of 500mm shall apply.


Page | 218

17th Edition Training Manual Section 740 - Temporary Electrical Installations for Structures, Amusement Devices and Booths at Fairgrounds, Amusement Parks and Circuses Some of the reasons why these installations are considered special installations/locations include: Temporary nature of the installation and the risks associated with the repetitive connection of these units and the risks associated with different connection provision at different locations.

With the constant transportation to locations there is risk of vibration problems due to trailer or vehicular movement and the effects of vibration and movement of structures during operation. 740.1.1 — Scope Section 740 relates to the safe design, installation and operation of temporary erected mobile or transportable electrical machines and structures which incorporate electrical equipment. This Section does NOT apply to: •

Internal electrical wiring of the machines (BS EN 60204-1).

•

Any permanent electrical installations that may supply such equipment.

740.313.1.1 — The nominal supply of temporary installations in booths, stands and amusement devices shall not exceed: •

230 V single-phase a.c..

•

400 V three-phase a.c.

•

440 V d.c.

740.313.3 — Irrespective of the number of sources of supplies, the line and neutral from different sources shall not be interconnected downstream of the origin of the temporary installation. Fig. 105 Fairground ride


740.410.3 — Protection against electric shock Automatic disconnection of the supply to the temporary electrical installation shall be provided by a 300mA RCD at

Page | 219

17th Edition Training Manual origin. A time delayed RCD can also be used provided there is other RCDs protecting the final circuits.

740.51 — Switchgear and controlgear shall be placed in cabinets which is only accessible with a key or tool.

740.411 — Supplies to a.c. motors, RCDs where used should be the time delay type to prevent unwanted tripping.

740.512.2 — External Influence All electrical equipment will have protection to IP44.

740.411.4.1 — In the UK, the ESQCR prohibit the use of a PME earthing facility for the supply for a caravan or similar construction.

740.52 — Wiring Systems

740.415 .1 — Additional protection ADS All circuits shall be protected by RCDs as specified in Regulation 415.1.1: •

Lighting

•

Socket-outlets

•

Mobile equipment up to 32A

Special note: The supply to a battery-operated emergency lighting circuit shall be connected to the same RCD protecting the circuit. 740.415.2 — Supplementary equipotential bonding, the connection between all exposed-conductive-parts and extraneous-conductive-part may be required in locations intended for livestock. If animals are kept in these locations reference to Section 705 may also need to be required. 740.422.3 — In the situation where stored materials may be considered a fire risk, a motor which is automatically or remotely controlled and is not supervised must be fitted with a manual reset to protect against excess temperature.


Cables installed in walkways which may be flexible to be suitably mechanically protected and flexible, they may also be installed in flexible conduit. (Cables of H07RNF and H07BN4-F with conduit to BS EN 61386-23 are deemed to comply with this requirement.) 740.526 — Joints to be avoided where ever possible. Where they are made, they are to be enclosed and have a degree of protection to IP4X or IPXXD. 740.537 — Every booth or stand to have its own means of isolation. This device willdisconnect all live conductors and not only be readily accessible, but properly identified for the circuit it protects. 740.55 — Equipment Luminaires and decorative lighting shall be suitably IP rated and fixed securely so that the weight of the lighting is not carried by the cable. Luminaires and decorative lighting fixed if below 2.5m (arms reach), must be guarded and firmly fixed to avoid injury due to heat concentration. 740.55 .1.2 — Insulation-piercing lampholders shall not be used unless the lampholders and cable are compatible and are non-removable. Page | 220

17th Edition Training Manual 740.55 .1.3 — All lamps in stalls where projectiles are used i.e. shooting galleries shall be protected against accidental damage. 740.55 .1.4 — All transportable floodlights to be inaccessible to the public. 740.55 .1.5 — All luminaires and floodlights to be mounted as not to considered a fire risk. 740.55 .3.2 — Separate circuit used to supply luminous tubes, signs or lamps to be controlled by an emergency switch. This will be easily visible, accessible and marked in accordance with the local authority requirements. 740.55 .7 — An adequate number of socket-outlets shall be installed and this is recommended to be one socket-outlet for every square metre.

The means of placing out of arm’s reach may be used. 740.551.8 — All generators to be placed in a location to prevent any inadvertent contact that imposes a risk of contact with hot surfaces or mechanical injury. These generators may require to be mounted on an antivibration mounting. The earthing arrangements with the use of earth electrodes must comply with Regulation 542.1 or 542.2 of BS 7671:2008. The neutral conductor of the star point of the generator will be connected to the exposed conductive parts of the generator, (Except an IT system). 740.6 — All equipment is to be inspected and tested after each site assembly.

Sockets to be identified for their intended dedication. When used outdoors be to BS EN 60309-2 or BSEN 60309-1. 740.55 .8 — Each amusement device shall be permanently marked to indicate the: •

Rated voltage

•

Rated current

•

Rated frequency

At its connection point. 740.55 .9 — Electric dodgems shall only be operated at voltages not exceeding50V a.c. or 120 V d.c. The circuit shall be electrically separated from the supply by means of a transformer to BS EN 61558-2-4 or a motor generator set.


Page | 221

17th Edition Training Manual Section 753 - Floor and Ceiling Heating Systems 753.1 — Scope Section 753 includes the installation of electric floor and ceiling heating systems erected either as:

The following Sections also have specific requirements relating floor and ceiling heating: Section 701 (bathrooms/shower rooms). Section 702 (Locations containing a swimming pool or other basin). Regulation Group 554.4 (the general requirements of 554.4 apply to all heating cables).

•

Thermal storage systems

•

Direct heating systems

•

NOT covered by Section 753:

753.411.3.2 — Protective measures ADS

•

Wall heating systems

•

Outdoor floor and ceiling heating systems

A 30mA RCD for automatic disconnection of supply shall be installed. Any metallic grid installed to be connected as an exposed conductive part. To avoid unwanted tripping the load to be limited to 7.5kW at 230V. 753.423 — Protection against burns In floor areas where contact with skin or footwear is possible, the surface temperature of the floor must be limited (for example 35 °C). 753.424.3.1 — Maximum temperatures are required for both the floor surface temperature and the zone where heating units are installed to be no greater than 80°C by the following measures: •

Appropriate design of the heating system.

•

Appropriate installation of the heating system to the manufacturers’ instructions.

Fig. 106 Underfloor electrical heating


•

Use of protective devices.

Page | 222

17th Edition Training Manual Heating units must be connected to the installation via cold leads or suitable terminals.Connection between cold leads and heating units must be inseparable (e.g. by crimping).

•

Conductors

•

Heated area

•

Rated voltage

Note:The cold tail (or cold lead) is the connection between the fixed installation and the heating.

•

Rated resistance of cold heating units

•

Rated current of overcurrent device

753.424.3.2 — Where the heating unit is pleased in an area close to easily ignitable material, special measures are required to be taken to ensure that under fault conditions, no risk occurs. This may be done by the placing of metal sheet or conduit.

•

Rated residual operating current of RCD

•

Insulation resistance of the heating unit

•

The leakage capacitance

753.512.2.5 — Ceiling heating will require to have a degree of protection no less than IPX1. Floor heating in concrete or similar to IPX7 and have appropriate mechanical properties. 753.514 — Identification and notices The designer will provide a plan for each heating system must be provided adjacent to the heating system distribution board. Details include: •

Manufacturer and type of units

•

Number

•

Length/area

•

Rated power

•

Surface power density

•

Layout

•

Position/depth of units

•

Position of junction boxes


753.515 — Elements not to cross expansion joints of the building structure. 753.520.4 — Heating-free areas Requirement for the attachment of room fittings to be provided in a way that heat emission is not prevented by such fittings. 753.522.4.3 — Where heating units are installed they will be heat-free areas where drilling and fixing by screws, nails or the like are permitted. This information needs to be given to other contractors to avoid any damage.

Page | 223

17th Edition Training Manual REVIEW QUESTIONS – Special Installations or Locations Question 1

Question 3

Zone 3 of a sauna is limited by a horizontal surface located above the floor at a height

Which protective measure for electrical installations in caravan parks is not permitted?

A.

0.7 m

A.

non-conducting location

B.

1.0 m

B.

extra-low voltage by SELV or PELV

C.

1.2 m

C.

electrical separation

D.

1.5 m

D.

double or reinforced isolation

Question 2

Question 4

Which one may NOT be used as a protective bonding conductor in a location where livestock is kept?

As a specific requirement for an insulation monitoring device (IMD) in a medical IT system, it's a.c. internal impedance must be more than

A.

Hot-dip galvanized steel strip with dimensions of 40 mm x 5 mm

B. C.

A.

150 kΩ

Hot-dip galvanized round steel of 4 mm diameter

B.

100 kΩ

Copper conductor having a cross-sectional area of 5

C.

80 kΩ

D.

50 kΩ

mm

2.

D.

Hot-dip galvanized round steel of10 mm diameter


Page | 224


Question 8

Identify one of the following which would be classed as a Group 2 medical location

In an area containing a bath or a shower, socket outlets must be installed

A.

Endoscopic room

A.

a minimum of 3m horizontally from zone 1 boundary

B.

Urology room

B.

3m horizontally from zone 0

C.

Haemodialysis room

C.

3m horizontally from zone 2

D.

Massage room

D.

within zone 2 but outside zone 1

Question 6

Question 9

A copper flexible cable used for connecting a mobile unit to the supply must have a minimum cross-sectional area of

In a bathroom zone 1 is defined as the A.

area outside a 0.60m circumference from the bath or shower

B.

area within a 0.60m circumference from the bath or shower

C.

area directly above the bath or shower up to 2.25m above the finished floor level

Question 7

D.

area within the bath or shower

Within agricultural premises, final circuits feeding socket outlets exceeding 32A should be protected by a

Question 10

A.

2.0 mm

B.

2.5 mm2

C.

3.0 mm2

D.

4.0 mm2

2

A.

100mA RCD

B.

10mA RCD

C.

300mA RCD

D.

250mA RCD


Photovoltaic equipment should always A.

be considered energised on the d.c. side

B.

be used in certain listed countries only

C.

be considered energised on the a.c. side

D.

use a low voltage supply

Page | 225


ANSWERS – Special Installations or Locations

1B, Ref: BS7671: 703.32.3 2B, Ref: BS7671: 705.544.2 3A, Ref: BS7671: 708.410.3.6 4B, Ref: BS7671: 710.411.6.3.1 5C, Ref: BS7671: Annex A710 6B, Ref: BS7671: 717.52.1 7A, Ref: BS7671: 705.411.1 8A, Ref: BS7671: 701.512.3 9C, Ref: BS7671: 701.32.3 10A, Ref: BS7671: 712.410.3


Page | 226


PART 8 – APPENDICES AppendicesOverview BS 7671 contains 16 listed Appendices, although Appendices 11 and 12 have been moved in Amendment 1. 1. British standards to which reference is made in the regulations 2. Statutory regulations and associated memoranda 3. Time/current characteristics of overcurrent protective devices and RCDs 4. Current-carrying capacity and voltage drop for cables 5. Classification of external influences 6. Model forms for certification and reporting 7. Harmonized cable core colours 8. Current-carrying capacity and voltage drop for busbar trunking and powertrack systems 9. Definitions — multiple source d.c. and other systems 10. Protection of conductors in parallel against overcurrent 11. Effect of harmonic currents on balanced three phase systems - moved to Appendix 4 Sections 5.5 and 5.6 in Amendment 1


12. Voltage drop in consumers’ installations - moved to Appendix 4 Section 6.4 in Amendment 1 13. Methods for measuring the insulation resistance/impedance of floors and walls to Earth or to the protective conductor system 14. Measurement of fault loop impedance: consideration of the increase of the resistance of the conductors with the increase of temperature 15. Ring and radial final circuit arrangements, Regulation 433.1 16. Devices for protection against overcurrent

Page | 227

17th Edition Training Manual Appendix 1:British Standards Referenced by the Regulations Appendix 1 is described as normative, all other appendices are informative. Normative means that this Appendix provides reference to documents which are the standards, for all the other appendices, they are informative, which means they provide additional information

These graphs use a logarithmic scale and this must be kept in mind or mistakes or miscalculations may be made. For this reason a table has been introduced for quick reference. The information within these graphs, are interrelated onto various other tables throughout BS7671 2008 i.e. tables 41.2 to 41.6 and also in the Onsite Guide.

Appendix 4: Current-Carrying Capacity and Voltage Drop for Cables and Flexible Cords

Appendix 2: Statutory Regulations and Associated Memoranda

This section has greatly changed from the previous 16th edition and care is required in the reading of this section.

Electrical installations are to comply with not only BS 7671 2008 but to specific Statutory Regulations. Refer to Appendix 2 for the up to date list of Statutory Regulations

Appendix 5: Classification of External Influences

Appendix 3:Time / Current Characteristics of Overcurrent Protective Devices and Residual Current Devices Appendix 3 provides the Time/current characteristics of overcurrent protective devices and RCDs. The characteristics are provided in the form of graphs and by plotting time in seconds against prospective current in amperes. By referencing the graphs the disconnection time of the selected device can be ascertained when the current passing through the device is known, conversely the current required to disconnect the device in a given time can also be known.


The Classification of External Influences is noticeably mentioned throughout BS7671 2008 and are intended to give the classification and codification of the external influences of the installation The First letter relates to the general category of the external influence. The Second letter relates to the nature of the external influence. The number relates to the class within the external influence, i.e. AD4 ‘A’ represents the Environment: •

Ambient temperature

•

Temperature and Humidity

Page | 228


Water

•

Foreign bodies

•

Corrosion

•

Impact

•

Vibration

•

Flora fauna

•

Electromagnetic

•

Solar

•

Seismic

•

Lighting

•

Lightning

•

Movement of air

•

Wind

‘B’ represents the Utilization of the building: •

Capability of the occupants

•

Contact of the occupants with Earth potential

•

Conditions of evacuation in an emergency

•

Nature of stored materials

‘C’ represents the construction of the building: •

Construction — combustible or non-combustible

•

Building design

It is recommended that installers and designers become familiar with these classifications. There is also a high probability of several exam questions occurring concerning external influence codes.


Appendix 6:Model Forms for Certification and Reporting. The forms required for the Certification of Electrical Installations are: •

The Electrical Installation Certificate

•

The Minor Electrical Installation Works Certificate

•

Electrical Installation Condition Repor (This replaces the Periodic Inspection Report in Amendment 1)

Further information on inspection and testing and periodic inspection, testing and reporting can be found in IET Guidance Note 3. The documentation above also requires: •

The Schedule of Inspections

•

The Schedule of Results

As mentioned in Part 6 Testing and Reporting of Electrical Installations is covered more thoroughly in qualifications such as the 2394 and 2395

Appendix 7:Harmonized Cable Core Colours This section indicates the colour identification and harmonization of conductors and the interconnection with existing installations.

Appendix 8: Current-Carrying Capacity and Voltage-Drop for Busbar Trunking and Page | 229

17th Edition Training Manual Powertrack Systems This addition to BS671 2008 for the 17th edition (from 16th), is for designers and installers to take volt-drop and currentcarrying-capacity of busbar trunking considerations into account, along with the manufacturer’s instructions.

Appendix 9:Definitions — Multiple Source, D.C. and Other Systems Covers specialized supply systems.

Appendix 10: Protection of Conductors in Parallel Against Overcurrent Provides information and guidance in relation to overcurrent protection (for overload and short-circuit currents) where conductors are connected in parallel (normally larger current designs).

Appendix 12: Volts Drop in Consumers Installations This Appendix has been deleted and the content moved to Appendix 4, Section 6.4

Appendix 13:Methods for Measuring the Insulation Resistance/Impedance of Floors & Walls to Earth or to the Protective Conductor System In previous editions of BS7671 this was incorporated in the section on testing. It has now been relocated in the appendices and cover the measurement of impedance or resistance of insulating floors and walls. It can be assumed that this is a specialized subject and is not addressed in everyday testing and reference is to be made to the Guidance note 3 concerning this procedure.

Appendix 11:Effect of Harmonic Currents on Balanced Three-Phase Systems This Appendix has been deleted and the content moved to Appendix 4, Sections 5.5 and 5.6


Page | 230

17th Edition Training Manual Appendix 14:Measurement of Earth Fault Loop Impedance: Consideration of the Increase of the Resistance of Conductors with Increase of Temperature Where there is a possibility that when a earth fault loop impedance tests are carried out on a circuit, the full load current will not be used and therefore, the maximum operating temperature will not be reached. The requirements of Regulations 411.4.5 and 411.5.4 are considered to be met if the following equation is applied.

𝑍𝑍(𝑚) = 0.8 ∗

voltage variations depending on time and place, changing of transformer taps and other considerations. Appendix 15: Ring and Radial Final Circuit Arrangements Sets out options for the design of ring and radial final circuits for household and similar premises

Appendix 16: Devices for protection against overvoltage Typical installation of a surge protective device (SPD) in a power distribution board for a TN-S system

𝑈𝑈 ∗ 𝐶𝐶𝐶𝐶 𝐼𝐼

Zs (m) is the measured impedance of the earth fault current loop up to the most distant point of the relevant circuit from the origin of the installation (Ω) Uo is the nominal a.c. rms line voltage to Earth (V) Ia is the current in amperes (A) causing operation of the protective device within the time stated in Table 41.1 or within 5 s according to the conditions stated in Regulation 411.3.2.3 (A). Cmin is the minimum voltage factor to take account of


Page | 231

17th Edition Training Manual REVIEW QUESTIONS – Appendices Question 1

Question 3

When determining design current, the correction factor that is applied to a BS3036 rewirable fuse is

BS EN 60228 relates to A.

conduit systems

A.

.752

B.

conductors of insulated cables

B.

.527

C.

cable trunking and ducting systems

C.

.725

D.

industrial plugs, couplers and socket outlets

D.

1.725

Question 4

Question 2

BS EN 60309 relates to

The correction factor for cables installed in free air with 70° thermosetting insulation and an ambient temperature of 50° is

A.

conduit systems

B.

conductors of insulated cables

C.

cable trunking and ducting systems

D.

industrial plugs, couplers and socket outlets

A.

.71

B.

.17

C.

.567

D.

.77


Question 5 On completion of a Electrical Installation Condition Report, the person ordering the report should be provided with A.

a duplicate copy of the report

B.

a summary of the report

C.

the 'original' of the report

D.

advice as to who can be contacted in order for the report to be viewed

Page | 232


Question 9

The code given to an area that has a high humidity level when classifying for external influences would be A.

AB

Where three or more conductors are connected in parallel, then multiple fault current paths can occur and it may therefore be necessary to provide

B.

AF

A.

C.

AA

short circuit protection at both the supply and the load end of each parallel conductor

D.

CB

B.

short circuit protection at the supply end only of each parallel conductor

Question 7

C.

When determining the current carrying capacity 'Iz' of a busbar trunking system, the rating factor 'ka' has to be applied to 'In' if the ambient temperature exceeds

short circuit protection at the load end only of each parallel conductor

D.

overload protection at the supply end only of each parallel conductor

A.

30°

B.

40°

C.

35°

D.

45°

Question 8 When referring to a TN-C-S multiple source system, the number of connections permitted between the interconnected neutral points of the sources and the PE conductor is A.

4

B.

2

C.

1

D.

3


Question 10 Measurement of the impedance of insulating floors and walls may be carried out with a lower voltage than the system voltage to earth, if combined with A.

a touch current measurement test

B.

an earth leakage measurement test

C.

a visual inspection

D.

an insulation resistance test

Page | 233

17th Edition Training Manual ANSWERS – Appendices 1C, Ref: BS7671: Appx 4, 4 2A, Ref: BS7671: Appx 4, Table 4B1 3B, Ref: BS7671: Appx 1 4D, Ref: BS7671: Appx 1 5C, Ref: BS7671: Appx 6, guidance for recipients 6A, Ref: BS7671: Appx 5 7C, Ref: BS7671: Appx 8, 2 8C, Ref: BS7671: Appx 9, Fig 9A 9A, Ref: BS7671: Appx 10, 3 10D, Ref: BS7671: Appx 13, 1


Page | 234


CITY & GUILDS 2382-15 SAMPLE EXAM QUESTIONS

Starting on the next page are 60 questions of the type which you might expect in the actual City & Guilds 2382-15 exam. As discussed earlier in this course, the exam takes place at an examination centre and is delivered online using the City & Guilds eVolve exam system.

Although the number and type of the following 60 questions are the same as those you will experience in the 2382-15, this is not an exam simulation, it is a practice to test your understanding of the course you have completed. Electacourse publishes a popular 17th Edition 2382-15 Exam Simulator which you can use to experience the actual exam. It can be purchased from electacourse.com, (note the exam simulator is for desktop and laptop computers only. In the real life exam you will have 2 hours to answer these 60 questions. Once you have completed these practice questions, use the answer sheet at the end to check your score and to view where in the Regulations the answers to the question will be found. The 60 questions are not sorted by section, this is how they are presented in the exam.


Page | 235

17th Edition Training Manual REVIEW QUESTIONS – City & Guilds 2382-15 Question 1

Question 3

BS7671 Wiring Regulations do NOT apply to the design, erection and verification of:

In a TN system, the maximum earth fault loop impedance Zs when using a 32 A , type B circuit breaker for instantaneous operation would be

A. railway traction equipment, rolling stock and signalling equipment

A.

1.37 Ω

B.

prefabricated buildings

B.

1.09 Ω

C.

commercial premises

C.

1.44 Ω

D.

medical locations

D.

0.72 Ω

Question 2

Question 4

A protective measure in which basic protection is provided by basic insulation of live parts or by barriers or enclosures and fault protection is provided by protective earthing, protective equipotential bonding and automatic disconnection in case of a fault is called

Where an electrode water heater or electrode boiler is connected to a three-phase low voltage supply, the shell of the electrode water heater or electrode boiler shall be connected to A.

the neutral of the supply

A.

Double or reinforced insulation

B.

to the earthing conductor

B.

Automatic disconnection of supply

C.

to the neutral of the supply AND to the earthing conductor

D.

to the neutral of the supply OR to the earthing conductor

C. Electrical separation for the supply to one item of current-using equipment D.

Extra-low voltage (SELV and PELV)


Page | 236


Question 7

In medical locations for transformers for IT systems the leakage current of the output winding to earth and the leakage current of the enclosure, when measured in no-load condition and the transformer supplied at rated voltage and rated frequency, shall not exceed

In each installation main protective bonding conductors shall connect to the main earthing terminal extraneous-conductiveparts including:

A.

0.5 mA

B.

1.0 mA

C.

1.5 mA

D.

2.5 mA

Question 6 BS7671 Wiring Regulations apply to the design, erection and verification of: A.

Equipment of mobile and fixed offshore installations

B.

Radio interference suppression equipment not affecting safety of the electrical installation

C.

Systems for the distribution of electricity to the public

D.

Equipment on board ships covered by BS 8450


A.


B.


C.

power supply

D.

multimedia network system cables

Question 8 The maximum disconnection time for a lighting circuit in a commercial premises protected by a TT system is A.

0.3 s

B.

0.2 s

C.

2s

D.

0.04 s

Page | 237


Question 12

Which one is NOT a thermal effect of radiant and convection energy on the surroundings in the selection and erection of a luminaire?

In each installation main protective bonding conductors shall connect to the main earthing terminal extraneous-conductiveparts including:

A.

A.

power supply

B.

metal fences

C.

Central heating and air conditioning systems

D.


the maximum permissible power dissipated by the lamps

B.

the efficiency of converting electric power to radiated power

C.

the minimum distance to combustible materials, including material in the path of a spotlight beam

D.

the fire-resistance of adjacent material

Question 10 In transformers for medical IT systems capacitors A.

may be used if necessary

B.

must be used

C.

shall not be used

D.

is recommended

Question 13 The maximum floor area served by a single 30A ring final circuit using socket outlets in a domestic installation is A.

25m2

B.

50m2

C.

75m2

D.

100m2

Question 14

Identify one of the following that is a non-statutory

Lighting circuits incorporating 15, B22, E14, E27 or E40 lamp holders shall be protected by an overcurrent protective device of maximum rating

A.

BS 7671:Requirements for Electrical Installations

A.

6A

B.

Electricity at Work Act

B.

10A

C.

Health and Safety at Work Act

C.

12A

D.

Cinematograph Regulations

D.

16A

Question 11


Page | 238


Question 18

The nominal d.c. supply voltage of the installation of the caravan shall not exceed

The current carrying capacity of a busbar trunking system is affected by its mounting conditions and

A.

12 V

A.

its IP rating

B.

24 V

B.

type of enclosure

C.

36 V

C.

external influences

D.

48 V

D.

ambient temperature

Question 16

Question 19

The fundamental principles of BS 7671 covering the protection against voltage disturbances etc., states that the installation design shall take into consideration the anticipated

Where a generating set is used as an additional source of supply in parallel with other sources, protection shall remain effective in all situations against overcurrent and

A.

weather conditions

A.

harmonic distortion

B.

load current

B.

high protective conductor currents

C.

electromagnetic emissions

C.

unbalance

D.

vibration

D.

thermal effects

Question 17

Question 20

Live parts shall be completely covered with insulation which can only be removed by A.

skilled persons

Restricted access areas where the protective measure of obstacles is applied the minimum height of gangway to barrier or enclosure above floor is

B.

destruction

A.

1800 mm

C.

instructed persons

B.

1900 mm

D.

special permission

C.

2000 mm

D.

2100 mm


Page | 239


Question 24

Temporary electrical installations erected for a particular purpose must be dismantled

Cable up to 10 mm2 surrounded by thermal insulation for 470mm of it's length has a derating factor of

A.

within 1 day after erection

A.

.51

B.

within 3 days after erection

B.

.63

C.

within 1 week after erection

C.

.78

D.

when no longer required for that purpose

D.

.88

Question 22

Question 25

Simultaneously accessible parts at different potentials A.

shall not be easily connected

Circuits within booths at fairground premises should be protected at the origin of an installation by at least a

B.

shall have basic insulation

A.

500mA RCD

C.

shall be protected by obstacles

B.

300mA RCD

D.

shall not be within arm's reach.

C.

100mA RCD

D.

10mA RCD

Question 23 An overcurrent protective device installed at the origin of a circuit must have a breaking capacity of

Question 26

A.

A.

basic protection only

B. equivalent or more than the prospective short circuit current

B.

fault protection only

C.

basic and fault protection

C.

twice the prospective short circuit current

D.

earth fault loop impedance fault protection

D.

equivalent to maximum earth fault current

at least 15kA


Class II equipment would provide

Page | 240


Question 29

In case of a fault, the maximum disconnection time for an a.c. circuit with nominal rms voltage in the range 50 V-120 V in a TN system (for final circuits not exceeding 32 A) is

Outdoor lighting involves all the following except

A.

0.8 sec

B.

0.4 sec

C.

0.2 sec

D.

0.1 sec

Question 28

A.

shelters

B.

road traffic signals

C.

flood lighting

D.

temporary festoon lighting

Question 30 Identify one of the following which would be classed as a Group 1 medical location

If frequency has an influence on the characteristics of the equipment, the rated frequency of the equipment shall correspond to

A.

operating plaster room

B.

intensive care room

A.

the average frequency of the supply to the circuit concerned.

C.

anaesthetic area

D.

physiotherapy room

B.

the maximum frequency of the supply to the circuit concerned.

Question 31

C.

the nominal power of the supply to the circuit concerned.

Which of the following does not need to be taken into account in the choice of methods of protection for safety and the selection and erection of equipment?

D.

the nominal frequency of the supply to the circuit concerned.

A.

Its maintainability

B.

The cost of equipment

C.

The compatibility of its equipment

D.

Assessment for continuity of service


Page | 241


Question 34

If it is necessary to remove a barrier or open an enclosure or remove parts of enclosures, this shall be possible

Identify which one of the following sources for safety services are recognised the IET Wiring Regulations incorporating Amendment 1

A.

by the use of a key or tool

B.

after disconnection of the supply to live parts against which the barriers or enclosures afford protection, restoration of the supply being possible only after replacement or re-closure of the barrier or enclosure

C.

D.

where an intermediate barrier providing a degree of protection of at least IPXXB or IP2X prevents contact with live parts, by the use of a key or tool to remove the intermediate barrier. by any of the three means

A.

primary cells

B.


C.

secondary cells

D.

solar energy cells

Question 35 A junction box can be installed within zone 1 of a swimming pool if it is A.

sealed using a suitable gasket sealant

Question 33

B.

protected by an RCD

The colour used for Protective conductor shall be

C.

supplied by SELV

A.

blue

D.

rated to IPX2

B.

black

C.

green-and-yellow

Question 36

D.

blue with green-and-yellow at the terminations.


Which of the following are NOT referred to in the regulations as current-carrying conductors in a.c. circuit under normal operating conditions A.

Single-phase 1-wire

B.

Single-phase 2-wire

C.

Single-phase 3-wire

D.

Two-phase 3-wire

Page | 242


Question 38

Where fixed equipment may attain surface temperatures which could cause a fire hazard to adjacent materials, one or more of the following installation methods shall be adopted. The equipment shall:

For groups containing non-sheathed or sheathed cables having different maximum operating temperatures, the current-carrying capacity of all the non-sheathed or sheathed cables in the group shall be based on

A.

A.

the average maximum operating temperature of any cable in the group together with the appropriate group rating factor.

B.

the highest maximum operating temperature of any cable in the group together with the appropriate group rating factor.

C.

the lowest maximum operating temperature of any cable in the group together with the appropriate group rating factor.

D.

ambient operating temperature of any cable in the group together with the appropriate group rating factor.

B.

C.

D.

be mounted on a support which has low thermal conductance or within an enclosure which will withstand, with minimal risk of fire or harmful thermal effect, such temperatures as may be generated be screened by materials of low thermal conductance which can withstand, with minimal risk of fire or harmful thermal effect, the heat emitted by the electrical equipment be mounted so as to allow safe dissipation of heat and at a sufficient distance from adjacent material on which such temperatures could have deleterious effects. Any means of support shall be of low thermal conductance any of the three applicable.


Question 39 An electrical installation certificate should be signed by A.

the local authority

B.

the installation designer

C.

a competent person

D.

a skilled person

Page | 243


Question 42

The socket outlet and it's enclosure, forming part of the pitch supply equipment for a caravan park, must comply with BS EN 60309-2 and have a minimum protection of A.

IP2X

B.

IP4X

Except for equipment for which an appropriate product standard specifies requirements a luminaire shall be kept at an adequate distance from combustible materials. Unless otherwise recommended by the manufacturer, a small spotlight or projector rated up to 100 W shall be installed at the following minimum distance from combustible materials:

C.

IP44

A.

0.3 m

D.

IP55

B.

0.4 m

Question 41

C.

0.5 m

Which characteristic of the supply or supplies does not need to be determined by calculation, measurement, enquiry or inspection?

D.

0.7 m

A. The type and rating of the overcurrent protective device(s) acting at the origin of the installation.

What is the minimum cross-sectional area for copper nonsheathed and sheathed cables used in lightning circuits?

B.

The nature of the current and frequency

A.

1.0 mm2

C.

The minimal voltage(s) and its characteristics

B.

2.0 mm2

D.

The earth fault loop impedance of that part of the system external to the installation, Ze

C.

3.0 mm2

D.

4.0 mm2


Question 43

Page | 244


Question 46

Which one is NOT an item for inspection checking?

Which characteristic of the supply or supplies does not need to be determined by calculation, measurement, enquiry or inspection?

A.

Availability of additional power sources

B.

Presence of diagrams, instructions and similar information

C.

Connection of conductors

D.

Presence of danger notices and other warning signs

A.

The nominal voltage(s) and its characteristics including harmonic distortion

B.

The suitability for the requirements of the installation, including the maximum demand

Question 45

C.

Which combination of electrical vehicles are within the scope of the EV regulations?

The prospective short-circuit current at the origin of the installation

D.

The maximum voltage(s) and its characteristics

A.

Mobility scooters alone

B.

Mobility scooters and electric cars

C.

Electric cars and bicycles

D.

Electric cars alone


Question 47 Except for equipment for which an appropriate product standard specifies requirements a luminaire shall be kept at an adequate distance from combustible materials. Unless otherwise recommended by the manufacturer, a small spotlight or projector rated over 300W up to 500 W shall be installed at the following minimum distance from combustible materials: A.

0.5 m

B.

0.8 m

C.

1.0 m

D.

1.5 m

Page | 245


Question 51

What is the minimum cross-sectional area for aluminium nonsheathed and sheathed cables used in lightning circuits?

Electrical installations shall be divided into circuits to A.

allow for more socket outlets

A.

10 mm

2

B.

reduce power usage

B.

16 mm

2

C.

C.

30 mm

2

allow for expansion without changing the maximum demand

D.

40 mm2

D.

minimise inconvenience in the event of a fault condition

Question 49 Which one is NOT an item for inspection checking?

Question 52

A. Presence of appropriate devices for isolation and switching correctly

Equipotential copper bonding designed as a bonding ring network must have a minimum round diameter of

B.

Identification of conductors

A.

8 mm

C.

Prevention of mutual detrimental influence

B.

10 mm

D.

Selection of methods of power switching

C.

12 mm

D.

15 mm

Question 50 A BS EN 60898 protective device is also known as a

Question 53

A.

circuit breaker

RCM stands for

B.

cartridge fuse

A.

Response current monitor

C.

RCD

B.

Residual current monitor

D.

semi enclosed rewirable fuse

C.

Residential current monitor

D.

Reduced current monitor


Page | 246


Question 57

An earth fault loop impedance test performed on a ring final circuit will record

The maximum Zs for a 10A Type°circuit breaker protecting a standard discharge type lighting circuit is

A.

the resistance of the protective conductor

A.

0.47Ω

B.

the resistance of the line conductor, protective conductor and external loop impedance

B.

0.57Ω

C.

2.30Ω

C.

the resistance of the line conductor and the protective conductor

D.

2.19Ω

D.

the external loop impedance

Question 58

Question 55 BS EN numbers specify compliance with A.

IEC Standards

B.

the Kite Mark

C.

BS Standard

D.

European Standards

Which one can serve as a part of a protective conductor? A.

A fixed bare or insulated conductor

B.

A gas pipe

C.

An oil pipe

D.

Support wires under mechanical stress

Question 59

Question 56

Which protective measure in medical locations is not permitted?

A suitable electrical source for safety services would be

A.

extra-low voltage by SELV or PELV

A.

storage batteries

B.

obstacles and placing out of reach

B.

a standard mains supply

C.

Automatic disconnection in case of a fault

C.

a generator connected to the mains supply

D.

double or reinforced isolation

D.

a supply not exceeding 50 v a.c.


Page | 247

17th Edition Training Manual Question 60 The external influence code AA2 relates to the ambient temperature range A.

-5° to +40°

B.

+5° to +40°

C.

-25° to +5°

D.

-40° to +5°

ANSWERS – City & Guilds 2382-15 1A, Ref: BS7671: 110.1.1, 110.2

12C, Ref: BS7671: 411.3.1.2

23B, Ref: BS7671: 434.5.1

2B, Ref: BS7671: 411.1

13D, Ref: BS7671: Appx 15, Fig 15A

24A, Ref: BS7671: 523.9

3A, Ref: BS7671: 411.4.7

14D, Ref: BS7671: 559.5.1.204

25B, Ref: BS7671: 740.410.3

4C, Ref: BS7671: 554.1.5

15D, Ref: BS7671: 721.313.1,2

26C, Ref: BS7671: N/A

5A, Ref: BS7671: 710.512.1.1

16C, Ref: BS7671: 131.6.4

27A, Ref: BS7671: 411.3.2.2

6B, Ref: BS7671: 110.1.1, 110.2

17B, Ref: BS7671: 416.1

28D, Ref: BS7671: 512.1.3

7A, Ref: BS7671: 411.3.1.2

18D, Ref: BS7671: Appx 8, 2

29D, Ref: BS7671: 714

8B, Ref: BS7671: 411.3.2

19D, Ref: BS7671: 551.7.1

30D, Ref: BS7671: Annex A710

9B, Ref: BS7671: 559.4.1

20C, Ref: BS7671: 729.513.2.2

31B, Ref: BS7671: 301.1

10C, Ref: BS7671: 710.512.1.1

21D, Ref: BS7671: Part 2: Definitions

32D, Ref: BS7671: 416.2.4

11A, Ref: BS7671: 114.1

22D, Ref: BS7671: 417.3.1

33C, Ref: BS7671: 514.4.2


Page | 248

17th Edition Training Manual 34A, Ref: BS7671: 560.6.1

44A, Ref: BS7671: 611.3

54B, Ref: BS7671: 612.9

35C, Ref: BS7671: 702.522.24

45D, Ref: BS7671: 722.1

55D, Ref: BS7671: Appx 1

36A, Ref: BS7671: 312.1.1

46D, Ref: BS7671: 313.1

56A, Ref: BS7671: 351.1

37D, Ref: BS7671: 421.1.2

47C, Ref: BS7671: 422.3.1

57D, Ref: BS7671: 411.4.7

38C, Ref: BS7671: 523.5

48B, Ref: BS7671: 524.2.3

58A, Ref: BS7671: 543.2.1, 543.2.2

39D, Ref: GN3: 1.2; BS7671: 610.5

49D, Ref: BS7671: 611.3

59B, Ref: BS7671: 710.410.3.5

40C, Ref: BS7671: 708.533.1.8

50A, Ref: BS7671: Appx 1

60D, Ref: BS7671: Appx 5

41C, Ref: BS7671: 313.1

51D, Ref: BS7671: 314.1

42C, Ref: BS7671: 422.3.1

52A, Ref: BS7671: 444.5.3

43A, Ref: BS7671: 524.2.3

53B, Ref: BS7671: 538.4


Page | 249


2382-15 EXAM SIMULATOR

The Electacourse 17th Edition 2382-15 Exam Simulator has been designed to accurately represent the real-life City & Guilds 238215 exam. The following pages illustrate the Exam Simulator to give an idea of what you might expect when you take the exam.


Page | 250



Page | 251



Page | 252



Page | 253



Page | 254


LIST OF ILLUSTRATIONS

Fig. 1 The IET, publisher of the Wiring Regulations ............. 12 Fig. 2 17th Edition Wiring Regulations, you can purchase the book new or second hand from Amazon. If you buy it second hand, make sure it does not have any pencil or pen markings inside. ......................................................................... 12 Fig. 3 The first electric street lamps in the UK ....................... 13 Fig. 4 Basic structure of the Regulations ................................. 19 Fig. 5 Structure of the 17th Edition Wiring Regulations....... 20 Fig. 6The 2382-15 exam is set and administered by City & Guilds........................................................................................... 21 Fig. 7 The number and percentage of questions for each section of the 2382-15 exam ...................................................... 22 Fig. 8 Page of the Regulations showing ‘dot’ numbering .... 27 Fig. 9 Outside scope of Regulations ........................................ 30 Fig. 11 Extra low voltage - Band I, telephone wiring (not part of BS7671) .................................................................................... 47 Fig. 12 Low voltage - Band II, domestic wiring (BS7671) ..... 47 Fig. 13 IP236S - Protection against solid bodies > 12.5mm (ie finger), water sprayed up to 60 Deg from vertical, 20 joule impact and manufacturer specific ........................................... 50 Fig. 14 RCD with test button .................................................... 67 Fig. 15 Supplementary bonding across the stop-cock........... 67 Fig. 16 Electrical cabinet providing basic protection ............ 68 Fig. 17 Examples of earthing to structural parts .................... 69 Fig. 18 Current path TN-S System ........................................... 70 Fig. 19 Fault current path - TN-S System ................................ 71 Fig. 21 Example of a hand held portable appliance indicating live and protected parts ............................................................ 77


Fig. 22 Do not connect to earth symbol ................................... 78 Fig. 23 A transformer ................................................................. 78 Fig. 24 SELV protects the user from electric shock in the case of a fault ....................................................................................... 79 Fig. 25 A common but not mandatory symbol for placing out of reach ......................................................................................... 80 Fig. 26 The consequence of arcing can be serious .................. 81 Fig. 25 Consumer unit - all cables are to pass through the same entry/exit hole ................................................................... 83 Fig. 26 A non-ferromagnetic metal or non-metallic entry plate is to be used ....................................................................... 83 Fig. 27 Ferro-magnetic fixing plate may be used provided slots are cut in plate between conductors ............................... 84 Fig. 26 Quooker, boiling water tap. An example of a new type of hot water producing appliance ................................... 86 Fig. 27 Overcurrent..................................................................... 88 Fig. 28 Distributor's overload device ....................................... 90 Fig. 29 Protection device not required ..................................... 92 Fig. 30 Harmonized wiring colours ....................................... 102 Fig. 31 Old and new wiring warning notice ......................... 103 Fig. 32 Complex wiring installation ....................................... 104 Fig. 35 Aftermath of fire at Shirley Towers in Southampton ..................................................................................................... 107 Fig. 33 We may not see sandstorms like this in the UK, but dust and particles can cause significant damage ................. 108 Fig. 34 Wiring supported by cable tray (in this example this is likely to be network cabling and not an electrical installation) ................................................................................ 110

Page | 255

17th Edition Training Manual Fig. 35 Installation design needs to take account of maintenance .............................................................................. 115 Fig. 36 RCD device ................................................................... 115 Fig. 37 A consumer unit with a clearly identified main switch. From January 2016, such units will be constructed of material according to regulation 421.1.201 ........................... 118 Fig. 38 A locked RCD with notice .......................................... 118 Fig. 39 Sign indicating presence of a fireman's switch ....... 120 Fig. 40 Fireman's switch including extraction control ........ 120 Fig. 41 RCM Monitor ............................................................... 121 Fig. 42 Main earthing terminal ............................................... 122 Fig. 43For a TN-S system, means shall be provided for the main earthing terminal of the installation to be connected to the earthed point of the source of energy.( Part of the connection may be formed by the distributor’s lines and equipment). ............................................................................... 124 Fig. 44For a TN-C-S system, where protective multiple earthing is provided, means shall be provided for the main earthing terminal of the installation to be connected by the distributor to the neutral of the source of energy ................ 125 Fig. 45For a TT or IT system, the main earthing terminal shall be connected via an earthing conductor to an earth electrode complying with Regulation 542.2. ........................ 126 Fig. 46 Earthing conductor...................................................... 129 Fig. 47 Disconnect by removing bolted link ......................... 129 Fig. 48 Protective conductors separately terminated .......... 136 Fig. 49 Sample label ................................................................. 137 Fig. 50 High protective current for sensitive equipment .... 137 Fig. 51 Earth clamp .................................................................. 140 Fig. 52 Supplementary bonding conductors and clamps ... 141


Fig. 53 Low voltage portable generator................................. 142 Fig. 54 Lathe - a rotating machine .......................................... 143 Fig. 55 Rotating machine stop switches ................................ 143 Fig. 56 Extension cable with couplers .................................... 144 Fig. 57 A single phase immersion heater is not considered to be an electrode boiler ............................................................... 145 Fig. 58 Underfloor heating ...................................................... 145 Fig. 62 Auxiliary circuit supplied directly from the main circuit .......................................................................................... 147 Fig. 63 Auxiliary circuit supplied from the main circuit via a rectifier ....................................................................................... 147 Fig. 64 Auxiliary circuit supplied from the main circuit via a transformer ................................................................................ 147 Fig. 59 Ceiling rose – pay regard to the particular requirements concerning ceiling lights and lampholders .. 150 Fig. 60 Symbols used in 559 Table 55.3 of BS7671................ 151 Fig. 61 Fire safety equipment .................................................. 152 Fig. 62 Illuminated fire exit sign ............................................. 154 Fig. 63 Continuity of conductors ............................................ 162 Fig. 64 Single phase insulation resistance ............................. 163 Fig. 65 Polarity test (part) ........................................................ 163 Fig. 66 Earth electrode test (one of many) ............................. 164 Fig. 67 Sample Electrical Installation Condition .................. 166 Fig. 68 If only all bathrooms were like this ........................... 172 Fig. 70 Low voltage circuits passing through the location require RCD protection ........................................................... 174 Fig. 77 Equipotential bonding in a bathroom (three water pipes bonded – 1. Hot water, 2. Cold water, 3. Heating) .... 176 Fig. 71 Shower isolator switch ................................................ 177 Fig. 72 In scope - swimming pools, Out of scope - beaches178

Page | 256

17th Edition Training Manual Fig. 73 Zone dimensions for swimming pools and paddling pools ........................................................................................... 179 Fig. 74 Zone dimensions for basin above ground ............... 179 Fig. 75 Plan of zones. See BS7671 Fig 702.3 for details, including where partitions are present ................................ 179 Fig. 76 Socket with non-conductive plate can be installed in Zone 1 where not possible to install elsewhere ................... 181 Fig. 77 Zones for fountains including air spray - see BS7671 Fig 702.4 ..................................................................................... 181 Fig. 78 Zone dimensions - sauna. Elevation ......................... 182 Fig. 79 Zone dimensions - sauna. Plan .................................. 182 Fig. 80 Electric sauna heater ................................................... 183 Fig. 81 Construction site electrical distribution equipment185 Fig. 82 Farm and farmyard ..................................................... 187 Fig. 83 Section 705 includes garden centres ......................... 187 Fig. 84 Pests such as rats and mice are a particular problem to protect against on agricultural locations .......................... 189 Fig. 85 Indication of earth bonding connections in a milking parlour ....................................................................................... 190 Fig. 86 Electrical supply point (includes water supply in this instance). Note voltage of 200-250V indicated by colour of socket ......................................................................................... 193


Fig. 87 Chichester marina - local to the publishers of this course ......................................................................................... 194 Fig. 88 Marina pedestal for the supply of electricity (and water) ......................................................................................... 197 Fig. 89 Hospital theatre room, but note, the specialist medical equipment is not part of BS7671 .............................. 198 Fig. 90 Illustration of patient environment. See BS7671 Figs 710.1 and 710.2 for full details ................................................ 202 Fig. 98 PV equipment on roof ................................................. 205 Fig. 91 PV Array warning notice ............................................ 206 Fig. 93 Bus shelters included in new regulation Special Locations 714 ............................................................................. 207 Fig. 92 Mobile medical unit ..................................................... 210 Fig. 102 Outside equipment .................................................... 211 Fig. 93 Caravan interior ........................................................... 213 Fig. 96 Electric vehicle charging is becoming an important of the electrical installation infrastructure................................. 216 Fig. 94 Passenger boarding bridge - a gangway .................. 217 Fig. 95 Fairground ride ............................................................ 219 Fig. 96 Underfloor electrical heating...................................... 222

Page | 257


LIST OF TABLES Table 1 External influence codes .............................................. 49 Table 2 IP Code - Protection against solids .......................... 52 Table 3 IP Code Protection against moisture ......................... 53 Table 4 Representation of sizes of solids of IP Code, first figure ............................................................................................ 54 Table 5 BS7671 Table 41.1 (page 53) ........................................ 72 Table 6 Requirements for documented risk assessment....... 73 Table 7 Risk assessment template ............................................ 74 Table 8 Voltage variation .......................................................... 75 Table 9 Zs values for circuits breakers .................................... 76 Table 9 BS7671 Table 42.1 - Temperature limit under normal load conditions for an accessible part of equipment within arm’s reach. ................................................................................. 85


Table 10 Derating factors for insulated cable - Table 52.2 of BS7671 ........................................................................................ 111 Table 12 Selection of protective, isolation and switching devices ........................................................................................ 117 Table 11 Minimum cross-sectional area of a buried earthing conductor. BS7671 Table 54.1 .................................................. 129 Table 12Cross-sectional areas of protective conductors. .... 130 Table 13 Representation by table of Regulations 544.2.1, .2, .3 relating to supplementary bonding conductor sizes ........... 139 Table 14 IP Rating for equipment installed outside on caravan park .............................................................................. 192 Table 15 IP Rating for marinas ............................................... 195 Table 16 RCD protection requirements ................................. 204

Page | 258


WHAT NEXT?

Now you have spent time studying the Regulations, you need to confirm your understanding by using the Electacourse 17th Edition 2382-15 Exam Simulator. The Exam Simulator contains nearly a thousand questions which will thoroughly test your ability to find your way around the Regulations. Practice with the Exam Simulator and once you are consistently getting above the 70% pass mark, you are ready for the City & Guilds 2382-15 Exam. Book with Electacourse and take the exam at one of our partner centres around the country. http://www.electacourse.com


Page | 259

17th Edition Training Manual

Recommend Documents