Electrical Skills Lab Manual

Engineering Department

s l l i k s l a c i r t c e l E

L A U N A

M Y R O T A R O B A L

AY 2015-2016 2015-2016

Course Code: EEPW2241 ID No.:

Name of the Student:

Section No.

Level:

Semester: 2 Specialization :

EEPW 2241: Electrical Skills Lab Manual

Updated by Mr. Murali Krishna Boddu & Mr. Mahesh Aphale

Shinas College of Technology

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CONTENTS Experiment Name of the Experiment No.

Page No.

Table of contents Course objectives, outcomes Course assessment scheme Laboratory rules General safety precautions and guidelines in the ELECTRICAL SKILLS lab Introduction 1

Electrical Supply

2

Measurement of the Earth Resistance

3

Preparation of Galvanized Steel Conduit

4

Wiring Lighting Circuit

5

Testing Wiring Circuits

6

Connection of Fluorescent Tube Light

7

Sodium Vapor Lamps

8

Connection and Trouble Shooting of Fan Circuit

9

Metal Halide Lamps


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COURSE OUTCOMES:

EEPW2241: ELECTRICAL SKILLS Prerequisites: Engineering Workshop (EEPW 1240) Goal: To provide the students with the concepts, techniques and applications of electrical workshop Objectives Outcomes This course should enable the Upon completion of the course, the student will be student to: able to: 1. Know the safety practices in the workshop and production areas. 2. Understand electrical techniques.

the

aspects of installation

3. Understand how to assemble steel conduit. 4. Understand how to lighting and circuits.

wire

5. Understand the concepts of construction of DC and singlephase AC motors. 6. Know different methods of protections. 7. Understand how to control circuits of single phase AC motors.

1. Familiarize and apply the electricity safety rules in Oman and in IEE regulation. 2. Describe the power distribution systems, Earthing arrangement, electrical bonding, PME supplies and current protective conductors. 3. Prepare for assembling steel conduit. 4. Wire lighting and power circuits. 5. Assemble and connect fluorescent and sodium vapour lamps. 6. Test the wiring circuits like visual inspection test, continuity test and insulation resistance test. 7. Define the fault diagnosis techniques in electrical insulations. 8. Describe the construction of DC and single phase AC motor. 9. Construct bell indictor circuits. 10. Apply different protection.

methods

of

circuit’s

11. Control the circuits of single-phase AC motors.


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Sources: I. Text Books 1. “Electrical Installation work, Brain McAdam, Elsevier 4Th Edition. 2. Electrical skills, Ministry Manual.

II. Reference Books 3. 4. 5. 6. 7. 8.

“Electrical Engineering, “Allen R Pearson Prentice Hall. “Basic Electrical Installation Work’’, Trevor Linsley, Newn ess(ACT) “Electrical Installation”, Thompson FG, Longman (NCT), 4Th Edition. “Electrical Technology”, BL Theraja & AK Theraja S Chand Publications. “Residential Construction Academy”, Stephen Herman, Thompson Publisher. “Electrical Instant Answer” Garg Tuck, MC Graw Hill Publications.

III. Web sites http://www.ehcoman.com http://www.majanco.co.om


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COURSE ASSESSMENT METHODS

Assessment Scheme (Total Practical Courses)

Course Grading Scheme Course Passing Grade

: 67-69 (C grade)*

* Depends on the course Marks 90-100 85-89 80-84 76-79 73-75 70-72 67-69 60-66 55-59 Below 55

Grade A AB+ B BC+ C CD F

GPA 4.0 3.7 3.3 3.0 2.7 2.3 2.0 1.7 1.0 0.0

Graduation Grading Scheme Below grade is displayed in the graduation certificate and it is based on the Overall CGPA of all levels. Overall CGPA 4 3.7-3.99 3.3-3.3.69 23-2. .2-. .2-.2 .23-.2. 92-92 923-92

0.0-.99

Grade A AB+ B BC+ C CD F

Descriptive Grade Excellent Very Good Good Satisfactory Fail


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Assessment Methods

(Total Practical Courses) Theory (T)

Practical (P) Lab report

Not Applicable

Viva-Voce

Written Questionnaire marks 100 % Practical part marks= Total marks out of 100

45 marks 15 marks 40

Assessment scheme for the Lab work Part I: Lab report with data collection and analysis – 45 Marks Part II: One Viva-voce – 15 marks Part III- Written questionnaire – 40 Marks In this part the student is subject to frequent written questionnaire about the performed experiments. It may include experimental data collection. A minimum of three written assessments are to be conducted (i.e. n > 3, where n= no. of practical assessments conducted). Best of (n-1) performances to be considered for final marks. All written assessments are announced.


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Attendance:



Issuing of Warning Letter Percentage Number of Hours First 10% Second 20% Third 30% If the absence reaches 30%, the student will be debarred from the final exam and will get ZERO in the final exam.



A student will be considered as LATE when s/he arrives after 10minutes of the class start time. Being LATE for THREE times in a class will be considered as ONE class absence.



The full course delivery plan must be covered. If students are absent without a valid reason, it will be considered as if the topic/s is already covered and will be included in exams.



If a student is absent for two continuous weeks within the semester in all courses, s/he will be DISMISSED from the College.

Absence Excuse:



If a student failed to attend any class, s/he has to submit the original excuse document within one week from the date of absence to registration department only.



If a student failed to attend midterm or final exam, s/he has to fill in a Supplementary Exam Form attached with the original excuse stamped from concern authorities and submit it to the registration department within one week from the exam date. Hospital/Clinic Attendance Certificate is not accepted as a valid excuse.



The coverage of topics in the midterm supplementary exam will include topics covered up to the midterm exam + topics covered one week after the midterm exam.



The final complementary exam will be conducted within four weeks from the start of next semester.


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Course Withdrawal

A student is allowed to withdraw one course during the semester. The withdrawal period will end a week after the midterm exam resultannouncement.

Submission of Assignment

20% of assignment scored mark will be reduced for each day of late submission. Cheating In case of an accusation of cheating during an examination is proven, the following will be imposed: Disciplinary Action for Cheating Case/s: 

First Offense (Zero Mark)



Second Offense (Study Suspension for one semester)



Third Offense (Dismissal from the College)


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Theory (T) Not Applicable

Practical (P) Lab report

45 Marks

Viva-Voce

15 Marks

Written Questionnaire 100 % Practical part marks= Total marks out of 100

40 Marks

Part I- Lab report with data collection and analysis – 45 marks No. 1 2 3 4

Factors Ability to follow procedure, data collection Data analysis, interpretation of results & conclusions related to the objectives and course outcomes Completeness, accuracy and correctness of data and results (Figures, graphs, tables, units, software) Submission on time Total

Marks 10 10 20 05 45 marks

Part II: One Viva-voce – 15 marks Part II- Written questionnaire – 40 marks In this part the student is subject to frequent written questionnaire about the performed experiments. It may include experimental data collection. A minimum of three written assessments are to be conducted (i.e. n > 3, where n= no. of practical assessments conducted). Best of (n-1) performances to be considered for final marks. All written assessments are announced.

Total weightage for all the above procedures (Part I + Part II+ Part III) is 100%


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WRITING LAB REPORT

1. Each Student has to write a Lab report on each Experiment / Exercise performed & submit the report within one week.

2. But if the student fails to submit the report within one week, he/she will loose 1 mark each day till the report is submitted.

3. After the completion of each experiment student must take the signature of course Lecturer on the cover page.

4. Attach the cover page to each Lab report before submission. 5. The report must be written on plane A4 sheets & preferably on both sides of the paper

6. Neat report with all the required data, graph, units and conclusion will get better marks.


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Dos and Don’ts:

Dos: 1.

Before starting Laboratory work follow all written and verbal instructions carefully. If you do not understand a direction or part of a procedure, ASK YOUR CONCERN TEACHER BEFORE PROCEEDING WITH THE ACTIVITY

2.

Do your wiring, setup, and a careful circuit checkout before applying power.

3.

Conduct yourself in a responsible manner at all times in the laboratory. D on’t talk aloud or crack jokes in lab.

4.

Appropriate Personal Protective Equipment should be worn during laboratory experiments.

5.

Do not eat food, drink beverages or chew gum in the laboratory and do not use laboratory glassware as containers for food or beverages. Smoking is strictly prohibited in lab area

Don’ts 1.

Avoid contact with energized electrical circuits.

2.

Do not make circuit changes or perform any wiring when power is on.

3.

Do not wear loose-fitting clothing or jewelry in the lab. Rings and necklaces are usual excellent conductors in contact with your skin.

4.

Do not touch anything if your hands are wet. The "one-hand" approach is safest.

5.

Do not wander around the room, distract other students, startle other students or interfere with the laboratory experiments of others


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Electrical Accidents/ Hazards are attributed to: 

Shock/ Electrocution



Arcing



Fire



Explosion

Which result in: 

Loss of Life



Loss of Property

Safety First SAFETY CLOTHING MUST BE WORN WORN Boys

SAFETY SHOES MUST BE

Girls


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Introduction Electricity and related water sector in Sultanate of Oman The Law for The Regulation and Privatization of the Electricity and Related Water Sector (the Sector Law) was promulgated by Royal Decree # 78/2004 and came into effect on 1 August 2004.

Reference : http://www.ehcoman.com


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Electricity Distribution in Oman: Geographical Coverage

Reference : http://www.ehcoman.com

Majan Electricity Company: Profile Majan through its systems, processes and people offers sustainable management of electricity with the purpose of serving the people of Oman by delivering safe, reliable and economical electricity. * Reference : http://www.majanco.co.om


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Regulation


Describe about

OES 1

33KV & 11KV Overhead Lines

OES 2

Underground Cables

OES 3

LT Overhead Lines

OES 4

Electrical Installations in Buildings

General Derogation OES 4 clause 6.5

Use of PVC Conduits

OES 5, 5A & 6

Transformers

OES 7, 21, 22, 23, 28 & 31

LT Equipment

OES 8,9,10,16,17,18,20,25, 26, 29 & 33

Overhead Line Material & Equipment

OES 11

General Specifications Electrical Equipment & Materials

OES 21A, 12B, 13, 14, 15, 19, 34 & 35

Switchgear & Associated Equipment

OES 24 3311KV

Indoor Substations

OES 27 Volume

1 132 33KV Substations

OES 27 Volume 2

132 33KV Substations

OES 30 33

11KV Outdoor Substation

OES 32

132KV OHL


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STANDARD OES 4 Ministry of Electricity and Water (now MHEW), Sultanate of Oman has issued REGULATIONS FOR ELECTRICAL INSTALLATIONS known as STANDARD OES 4 which is available at http://www.aer-oman.org

BS 7671:2008 •

•

•

•

This British Standard specifies the “Requirements for Electrical Installations” It is also known as IEE Wiring Regulations The regulations apply to the design, erection, and verification of electrical installations. These regulations are updated and applicable in the region.


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STANDARD OES 4 Scope and Coverage (Where to use the standard?) The regulations apply to electrical installations such as those of, –

Residential Premises

–

Commercial Premises

–

Public Premises

–

Industrial Premises

–

Agricultural and Horticultural Premises

–

Prefabricated Buildings

–

Construction Sites, Exhibitions, Fairs and other temporary installations.

The regulations cover, –

–

–

Circuits supplied at normal voltages up to and including 415/240 V AC 50 Hz. Any wiring not specifically covered by the specifications of appliances. Fixed wiring for telecommunications, signaling, control (excluding external wiring of apparatus).

Reference: STANDARD OES 4, SECOND EDITION, MAY 1989


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ELECTRICAL STANDARD Compliance with Regulations (Why to use/meet the standard?) Compliance with electrical regulations is essential to ensure safety of life, plant, equipment and buildings especially from the hazards of fire, electrical shocks and mishaps in the utilization of electricity in and around buildings. PROTECTION AGAINST ELECTRIC SHOCK In electrical installations, one of the major risks is electric shock. Persons and livestock (animals) shall be protected against dangers that may arise, a. from contact with live parts of the installation by: –

–

appropriate measures to prevent contact; ISOLATION Limiting the value and duration of current which can pass through a body to a value lower than shock current. INSULATION

b. From contact with exposed metal parts by one of the following methods. –

–

–

Preventing a fault current from passing through the body of any person or any livestock. EARTHING Limiting the value and duration of current which can pass through a body to a value lower than shock current. INSULATION Automatic disconnection of the supply on the occurrence of a fault likely to cause a current to flow through a body in contact with the exposed metal parts, where the value of the current is equal to or greater than the shock current . ISOLATION

PROTECTION AGAINST THERMAL EFFECTS Another major risk with the electrical installations is excessive temperature likely to cause burns, fires and other injurious effects. Protection shall be provided against –

–

The harmful effects of heat or thermal radiation developed by electrical equipment. Ignition, combustion or degradation or material.

Reference: BS7671-2008 –

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


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EEPW 2241: Electrical Skills Lab Manual –


Safety services being cutoff by the failure of electrical equipment.

PROTECTION AGAINST OVERCURRENT Persons or livestock shall be protected against injury and property shall be protected against damage due to excessive temperatures or electro-mechanical stresses caused by over currents likely to arise in live conductors by, –

–

Automatic disconnection on the occurrence of over-current before the overcurrent attains a dangerous value taking into account its duration. Limiting the maximum over-current to a safe value and duration.

Conductors other than live conductors and any other parts intended to carry a fault-current shall be capable of carrying that current without assuming excessive temperature. PROTECTION AGAINST VOLTAGE DISTURBANCES AND ELECTROMAGNETIC DISTURBANCES Shall cover, –

Protection of low voltage installations against temporary over-voltages due to earth fault in high voltage systems and due to faults in the low voltage systems.

–

Protection against over-voltages of atmospheric origin or due to switching.

–

Measures against electromagnetic influences.

–

Protection against under voltages

Reference: BS7671-2008


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Compliance with OES4 is achieved through following steps: (How to meet the Standard?) 1. Submission of Drawings: Schematic and wiring diagrams, layout drawings and schedule of points with site layout should be submitted to the Ministry before commencement of any electrical work whatsoever large or small, new or additions, and work shall start only after due approval of the Ministry. All work should be carried out in accordance with the approved drawings. 2. Inspection: All installation work will be subject to inspection and testing by the ministry and will be connected to the power supply only after the work is checked and approved by the ministry. 3. Electrical Supervision: All electrical installation works shall be carried out by or under the direct supervision of a qualified electrical engineer or a supervisor holding a competency license issued by the Ministry. Such competency license will be issued after necessary tests and interview by the Ministry. 4. Standards, Materials and Workmanship: The works shall be carried out in a neat and workmanlike manner to meet the requirements of these regulations. All materials used shall be the best of their respective kinds and shall comply with the latest relevant recommendations of the International Electro-technical Commission (IEC) if available and if no IEC recommendation is available with the latest relevant British Standard Specification (BSS)

Reference: STANDARD OES 4, SECOND EDITION, MAY 1989


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Exercise 1: Electrical Supply Aim: To understand different types of supply systems and trace the electrical supply system in Shinas College of Technology (After discussion of the topic in class the students will be taken around the campus of the institute to trace the electrical supply system) Electrical Power System in Oman:


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Electrical supply at the consumers (domestic/ commercial/ industrial) is drawn from distribution substations. Depending on the applications and KVA the supply voltage is 11kV or 400 V. The distribution substations are equipped with necessary means for isolation and protection. Bulk consumers of electricity such as Shinas College of Technology receive electrical supply at 11kV from distribution substation. In the consumer premises, the consumer has another substation to step down this voltage to 400V to meet lighting and low voltage applications.


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: m a r g a i d g n i w o l l o f e h t n i d e y a l p s i d s i m e t s y s a h c u s f o m a r g a i d c i t a m e h c S


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Exercise 1: Electrical Supply Systems: Reference: Chapter 7, Advanced Electrical Installation Work, Fifth Edition, Publication: Newens Author: Trevour Linsley

As per the Electricity Regulations applicable in the region to ensure safety, electrical installations must be equipped with 1. Basic protection and 2. Fault protection

This protection is provided using principle of “Protective equi -potential bonding coupled with automatic disconnection of supply” . In this method all exposed metal work is electrically connected together to an effective earth connection.

This expose metalwork includes,  Electrical conduits  Trunking  Metal switches  Metalwork of electrical appliances  Water service pipes  Gas and other service pipes and ducting  Central heating and air conditioning systems  Exposed metallic structural parts of the building  Lightening protective systems


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There are three commonly used arrangements of the earthing connection as described in IEE Electricity Regulations which are discussed here. TN-S System  TN-C-S System  TT System These have been designated in the IEE Regulations using the letters: T, N, C and S. These letters stand for: T - terre (French for earth) and meaning a direct connection to earth. N - neutral C - combined S - separate. When these letters are grouped, they form the classification of a type of system. The first letter denotes how the supply source is earthed. The second denotes how the metalwork of an installation is earthed. The third and fourth indicate the functions of neutral and protective conductors. 


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TN-S System (Cable Sheath Earth Supply)



Used where the electricity company’s supply is provided by underground cables.



Neutral and protective conductors CP (also called as protective earth PE) are separate throughout the system.



The protective earth conductor (PE) is the metal sheath and armour of the underground cable and this is connected to the consumer’s main earthing terminal.



All exposed metalwork is connected to the protective conductor via the main earthing terminal of the installation.


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

This system has the neutral of power supply with connection of earth only at one point to the source. The consumer’s earthing terminal is usually connected to the metallic Armour of the distributor’s cable into the HV / LV transformer.



It is commonly used for underground power supply to the premise or factory from the distributor substation to customer substation. This earth terminal is connected by the supply protective conductor (PE) back to the star point (neutral) of the secondary winding of the supply transformer, which is also connected at that point to an earth electrode.


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TN-C-S System (Protective Multiple Earthing Supply)


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

The supply cable uses a combined protective earth & neutral (PEN) conductor.



At the supply intake point a consumer’s main earthing termi nal is formed by connecting the earthing terminal to the neutral conductor.



All exposed conductive parts of the installation are then connected to the main earthing terminals. Thus phase to earth faults are effectively converted into phase to neutral faults


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TT System (No Earth Provided Supply)



installations protective conductor must be connected to earth via an earth electrode provided by the consumer. The TT method is used mostly in country areas with overhead transmission lines.



In contrast to the TN-S system there is no metallic path from the consumer's terminals back to the sub-station transformer secondary windings. Because the earth path may be of high resistance, a residual current circuit-breaker (R.C.C.B.) is often fitted so that if a fault current flows in the earth path then a trip disconnects the phase supply. For protection against indirect contact in domestic premises, every socket outlet requires an RCCB with a maximum rated current of 30mA.


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Residual Current Protection RCDs are designed to disconnect the circuit if there is a leakage current. By detecting small leakage currents (typically 5–30 mA) and disconnecting quickly enough (<300 ms), they may prevent electrocution. They are an essential part of the automatic disconnection of supply (ADS), i.e. to switch off when a fault develops, rather than rely on human intervention; this is one of the essential tenets of modern electrical practice. By contrast, conventional circuit breakers or fuses only break the circuit when the total current is excessive (which may be thousands of times the leakage current an RCD responds to). A small leakage current, such as through a person, can be a very serious fault, but would probably not increase the total current enough for a fuse or circuit breaker to break the circuit, and certainly not to do so fast enough to save a life.


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Advantages 1. They are less sensitive to fault conditions. 2. While voltage and current on the earth line is usually fault current from a live wire, this is not always the case, thus there are situations in which an ELCB can nuisance trip. 3. When an installation has two connections to earth, a nearby high current lightning strike will cause a voltage gradient in the soil, presenting the ELCB sense coil with enough voltage to cause it to trip. 4. If the installation’s earth rod is placed close to the earth rod of a neighboring building, a high earth leakage current in the other building can raise the local ground potential and cause a voltage difference across the two earths, again tripping the ELCB. 5. If there is an accumulated or burden of currents caused by items with lowered insulation resistance due to older equipment, or with heating elements, or rain conditions can cause the insulation resistance to lower due to moisture tracking. If there is a some mA who is equal to ELCB rating than ELCB may give nuisance Tripping. 6. If either of the earth wires become disconnected from the ELCB, it will no longer trip or the installation will often no longer be properly earthed. 7. Some ELCBs do not respond to rectified fault current. This issue is common for ELCBs and RCDs, but ELCBs are on average much older than RCB so an old ELCB is more likely to have some uncommon fault current waveform that it will not respond to. 8. Voltage-operated ELCB are the requirement for a second connection, and the possibility that any additional connection to earth on the protected system can disable the detector. 9. Nuisance tripping especially during thunderstorms.


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Disadvantages 1. They do not detect faults that don’t pass current through the CPC to the earth rod. 2. They do not allow a single building system to be easily split into multiple sections with independent fault protection, because earthing systems are usually use common earth Rod. 3. They may be tripped by external voltages from something connected to the earthing system such as metal pipes, a TN-S earth or a TN-C-S combined neutral and earth. 4. As electrically leaky appliances such as some water heaters, washing machines and cookers may cause the ELCB to trip. 5. ELCBs introduce additional resistance and an additional point of failure into the earthing system.

Answer following questions: 1) Why and where protection is required in the Electrical Installations?

2) Where we can use the earthing systems? a) TN – S System b) TN – C – S System c) TT System

3) What is RCD? How does it work?

4) What is the supply voltage obtained from the electricity board to Shinas college of Technology? 5) What is the kVA rating of the distribution substation in the college premises?

6) What is the type of transformer in the substation?

7) How much voltage is required at the consumer’s premises for Lighting and low voltage applications?


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Exercise 2: Measurement of the Earth Resistance STANDARD, OES4 Section 4.2.9 CONSUMER EARTING SYSTEM An independent, separate earthing system shall be installed and maintained by the consumer. This shall comprise the following, 

Earth electrode of 15mm diameter copper earth rod set with driving pin and head driven to a minimum depth of 3 meters. This shall be installed as near to the consumer’s main board as possible inside earth pit with inspection cover as per figure 2.1. The earth electrode shall include a corrosion resistant terminal clamp.



PVC insulated stranded copper earth conductor (35 mm 2 copper for single consumer

installation

and

70

mm 2 copper

multiple

consumer

installation) with cramped terminal lugs, shall be connected between the earth electrode and the consumer’s main earthing terminal or bar. 

PVC insulated earth continuity conductor of every outgoing circuit from the consumer’s main board shall be connected to the main earthing terminal.



The resistance of the consumer’s earthing system to the general mass of earth shall not exceed 50 Ω. To achieve this value in the areas of high soil resistivity, additional earth electrodes with a minimum spacing of 3 meters shall be installed.



Consumer’s earth electrode resistance shall be measured in accordance with the method described in Appendix VI of the OES4.



All metal work, exposed conductive parts and enclosures, in the consumer’s installation (other than live conductors and current carrying parts) shall be connected with PVC insulated earth continuity conductor to the main earthing terminal.



The consumer’s earthing system shall be connected to the MEW (electricity Distribution Company) earthing system.



The neutral conductor shall remain insulated throughout the installation and shall not at any point be connected to the earthing system.


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(Note: all dimensions are in mm ) Figure 2.1: Earth Pit


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Aim: To measure the value of earth resistance and earth voltage by using Earth Resistance Tester (Kyoritsu 4102A).

Apparatus Required: 1) Earth resistance tester

- 1 No.

2) Connecting leads

- 3 Nos.

3) Earth Electrodes

- 2 Nos.

4) Hammer

- 1 No.

Theory: The importance of earthing lies in the fact that it deals with safety. The word ‘earthing’ comes from the fact tha t the technique itself involves making a lowresistance connection to the earth or to the ground. The earth is considered to be a large conductor which is at zero potential. Reason for Earthing: The basic reason for earthing is to prevent or minimize the risk of shock to human beings and livestock by providing a low resistance discharge path for earth leakage currents which would otherwise provide injuries or even death to a person or animal touching the metal part. The following diagram describes the degree of danger of the leakage current; if, it flows in the human body.


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The following example through the figures describes how the earthing system works: In the following diagram the metallic part is not earthed and the human being is touching it.

Let, The supply voltage is 240V, AC circuit. The apparatus is having 40Ω and the defective insulation is making the metallic body live and it is not earthed. Let the body resistance is 1000Ω:

As shown above the leakage current may cause death to the person that is in contact with the metallic part. The fuse in the path will not be able to identify the small rise in current. In the following diagram the metallic part is earthed and the human being is touching it. With the same supply system let, the sum of the resistance of cable and the metallic part be 10Ω

Now the current is 4.8 times the fuse rating current. So, the fuse will operate and protect the human by: i. Blowing out and separating the supply from the body in touch with the equipment ii. By making the potential across the body ‘Zero’ (i.e. a shorted electric part through the earth wires).


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Types of earth electrodes: Rod and pipe electrodes: The following drawing describes how such electrodes are used in a distribution wiring system:

Plate electrodes:


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The following drawing describes how such electrodes are used in a distribution wiring system:


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Preparation for Measurement: A) Mechanical Zero Adjustment To obtain a measurement value with high accuracy, rotate the meter zero adjuster with a screwdriver with the range selector switch OFF, and surely match the indicator to “0” graduation value at the left of the scale board. B) Connecting Connecting Test Probe Insert the plug of the probe securely into the terminals of the instrument. Loose connection may result in inaccurate measurements. C) Battery Voltage Check Set the range selector switch to BATT.CHECK position and press the test button. Then the indicator swings, make sure that the indicator is at the right of BATT.GOOD graduation borderline on the scale board. Otherwise, the batteries are exhausted.

Connection Diagram:


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Procedure: 1) Strike the auxiliary earth spikes P and C into the ground deeply. They should be aligned at and interval of 5 -10 meters from the earthed equipment under test. 2) Connect the Green Green Wire to the earthed equipment under test, Yellow Yellow to the auxiliary earth spike P and the Red to Red to the auxiliary earth spike C from terminals E, P and C of the instrument respectively. 3) Set the range switch to EARTH VOLTAGE position to check earth voltage. Record the reading in table below. 4) Set the range switch to × 100

positions,

and press the test button. The LED

remains illuminated during testing. Turn the range switch to × 10

 and

×1



when the earth resistance is low. This indicated value is the EARTH E ARTH RESISTANCE of the earthed equipment under test. 5) Change the spike ‘P’ position to 2m, 4m, 6m, 8m, 10m from the earth pin ‘E’ and note down the earth resistance and tabulate the readings. Observations: Distance From the Earth Pin ‘E’ to the Spike P

Earth Resistance Observed Resistance Observed Value (Unit)

2m 4m 6m 8m 10 m


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Graph The variation of earth resistance with distance

Conclusions: Answer Following Questions,   

Why is it necessary to provide earthing? From the observations above, comment if the earth resistance measured is acceptable as per the OES 4. If the value of resistance is unacceptable, what are the measures required to bring it to the acceptable range?


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Exercise 3: Preparation of Galvanized Steel Conduit STANDARD, OES 4 Section 3.13 Steel Conduits and fittings for use in building electrical installations shall comply with BS 4568, Parts 1 and 2 of heavy gauge hot dip galvanized inside and outside, screwed type. Section 6.1 Installation of Conduits The conduits for each circuit shall be completely installed before any cable is drawn in. Conduits shall be securely fixed and where they are liable to mechanical damage they shall be adequately protected. Provision for the safe and easy drawing in of cables shall be made by use of inspection fittings, draw boxes. Provisions shall be such that cables can be drawn in or replaced without the cables being damaged or conduit dismantled. All runs of the conduit shall be truly vertical or horizontal. Section 6.2 Conduit Saddles Where conduits are installed on the surface of building fabric they shall be supported by purpose made conduit saddles or spacer bar saddles. Supports shall be provided at a maximum spacing of 1500 mm for galvanized steel conduits and 1200 mm for high impact PVC conduit. Section 6.3 Smooth Finish of Conduits The boxes of all the conduits shall be smooth and free from projection which may injure cables or obstruct their drawing in. ends of conduits shall be so reamed and when they terminate at boxes, trunking and accessories not fitted with spout entries, shall be so bushed as to obviate abrasion of cables.


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Section 6.4 Radius of Bend The radius of every conduit bend shall not be less than 2.5 times the outside diameter of the conduit. Section 6.5 Galvanized Steel Conduits Galvanized Steel conduit system shall be earthed and connected to the earthcontinuity conductor. All joints shall be made mechanically and electrically continuous by screwing. The conduit shall not however be used as an earth continuity conductor and a separate earth continuity cable shall be drawn into the conduit for every final sub-circuit. Only Galvanized Steel conduits shall be used in the space between a roof and suspended false ceiling, in situations subject to fire risk and in surface mounted industrial installation. PVC conduits shall not be used for such applications. (Derogation issued in2009 to use PVC conduits) Galvanized Steel conduits shall not be used under floor tiles of buildings or in concealed wiring systems embedded in walls or floors. PVC conduits shall be used for all such applications. Section 6.6 PVC Conduits and Fittings PVC conduits and fittings shall be of the unthreaded type. All joints shall be made with vinyl cement and entries of all conduit fittings shall be designed such that reliable water tight joints can be obtained. Surface mounted PVC conduit systems shall be so supported as to allow for longitudinal expansion and contraction. A cement that shall remain in adhesive plasticized state shall be used for expansion couplers. Section 6.7 Flexible Conduits Flexible conduits shall only be used for the final connection of motors and other equipment subject to vibration or adjustment of position. PVC flexible conduits and fittings shall comply with BS 4607 part 3. Metallic flexible conduits and fittings shall comply with BS 731 Part 1 and shall preferable be provided with an outer sheath of PVC. Flexible metal conduit shall not be used as the sole means of providing earth continuity and a separate earth continuity cable shall be provided.


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Where necessary, flexible conduit shall be adequately supported and / or protected. In damp or wet situations flexible conduits shall be watertight and remain impervious to ingress of water or moisture. The ends of flexible conduit shall be securely anchored to fixed conduit and / or equipment entries by purpose made flexible conduit adaptors. Section 6.8 Conduit Sizes Conduits shall be limited to the following sizes 16 mm, 20 mm, 25 mm, 32 mm and 50 mm


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Aim: To make the Galvanized Steel conduit to do the wiring for the following measurement. 1) Making 900 bend from a fixed point. 2) Making two 900 set. 3) Making thread for 1.5 cm at one end. Tools Required: 1) Steel Pipe Bending Vice 2) Steel Pipe 3) Threading Die 4) Hand File 5) Wire Brush 6) Measuring Tape 7) Marker Pen

- 1 No. - 1 No. - 1 No. - 1 No. - 1 No. - 1 No. - 1 No.

Cutting: Conduit pipes can be cut by using a hacksaw or a pipe cutter as shown in the following figures:

Procedure: 1. Fix the conduit in the vice so that the vice grips the conduit 50 or 75mm from the point where the cut has to be made 2. The blade is to be installed so that the cut is made on the forward stroke. Precautions: a. After cutting by any method the inside edge of the conduit must be smoothed with half round file as shown in the figure. b. Be sure that the ridge is cleared before installing the pipe for wiring. c.


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Threading: When short lengths of conduits are to be used for switch or lamp drops, the end of the pipe needs to be threaded to enable fixing of the conduit to the accessories. The threads on the conduit in all cases shall be between 11mm to 27mm long. This threading of conduit is done by using dies and a die-stock. Note: 1. Apply cutting oil to the end before starting to cut threads. 2. Cutting threads longer than necessary will leave exposed threads that are not protected from corrosion. Precaution: a. Use only a brush to remove the metal burrs from the die. Do not use your hand. Metal conduit boxes and the symbols used in metal conduit wiring: The following figure shows different popular outlet boxes used in metal conduit wiring:


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Following figure shows the various symbols used for different boxes in a single line diagram for such a wiring:

The following figure shows the wall and ceiling boxes for conduit wiring, a switching box is also displayed:


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Preparing the boxes for the conduit wiring: The boxes can be used after removing the knock-outs in the boxes. The knock-outs can be removed from the boxes by using any of the method shown in the following figures:

After removing the knockouts the boxes are prepared as shown in the following figure:


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Conduit pipe bending: It is often necessary to set or bend the conduit to enable it to pass over an obstruction as shown in the following figure:

The bending can be made by using: a. Simple bending block:

b.

Simple bending hickey:


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EEPW 2241: Electrical Skills Lab Manual c.


Using a bending machine:

d

  160 

8 

Actual radius of bend = inner radius of the pulley

8

d = outer diameter of the bending pulley

63 mm

60 mm

80 mm

Pulley


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Procedure: 1. Measure diameter of the Galvanized Steel Pipe given for the exercise. 2. Select suitable pulley for bending the pipe. 3. Making 900 bend from a fixed point. 1) Take a steel pipe of length 900 mm and mark 300 mm from the edge or a fixed point consider that mark as an initial mark. 900 300

2) Add

1 8

th of the outer circumference of the bending pulley from the initial mark

Example: 300mm + (

300

  160

8

) =363 mm and consider this as a new mark.

63 mm

3) Place the tube in the former with the fixed point at the rear and place the pipe exactly at the new mark which should be aligned with the perpendicular scale. 4) This will give a 900 bend at the required distance from the fixed point to the back of the bend.

300 mm

4. Making two 900 set: 1) From initial mark of 300 mm, measure another 300 mm and mark.


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2) Take this new mark as reference, subtract

1 8

th of

the outer circumference of the

bending pulley. Consider this as reference mark for the second bend. 300 mm

63 mm

300 mm

3) Now measure the gap between two bends. If you get 300mm from center to center of the bends means your work is carried out successfully.

300 mm

300 mm

300 mm

5. Making thread at one end: 1) Mark the threading length in the steel pipe from the fixed end. Take the die and fix it with the tool used for making the thread. 2) Place the threading tool at the edge of the pipe and rotate it in forward direction for one full circle and rotate in opposite direction for one full circle.


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3) Repeat the same thing until the full thread is made at one end as per the measurement.

S.No

Quantity

1

Length of pipe used

2

Size of Pipe used

3

The angle made at one end

4

The angle made at other end

5

Radius of the bend

6

Distance between the bends

7

Distance from one end to center of the bend

Measurement

Results: 1. Mention the various types of conduits. 2. What are the available sizes of conduits used in industry? 3. Mention the applications of various types of conduits. 4. Mention the precautions taken while performing the exercise?


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Exercise 4: Wiring Lighting Circuit STANDARD OES 4 Section 4.2.10 Connection of Switch and Control Gear Switches, circuit breakers, fuses, thermostats and similar control devices shall be connected in live (phase) conductor only, a bolted or screwed link being connected in the neutral conductor. If the switch or circuit breaker includes an isolating neutral link, it shall be arranged to make before and open after the live (phase) poles. Section 4.2.17 Load on lighting circuits Load on lighting circuits in domestic installations shall not exceed 1500 W per final sub circuit. Section 4.2.20 Lighting Switches Local switches for lighting points and for appliances not connected to socket outlets shall have a minimum current rating of 5A. For outdoor and industrial use, switches shall be metal clad and water tight. Switches for control of discharge lighting shall have a current rating of not less than twice the steady state continuous current of the circuit. All local switches shall be mounted in readily accessible positions with the dollies at the minimum height of 1250 mm from finished floor level. In kitchens and in situations other than bathrooms, where water is regularly used no switch shall be mounted within 2 meters of any tap, basin, sink, if this is not possible, ceiling mounted insulating cord operated switches shall be used. In bathroom and toilets, switches shall be of the ceiling mounted insulating cord operated type. If wall mounted switches are used for control of lighting and exhaust fans, same shall be located in an accessible position outside the bathroom or toilet and immediately adjacent to the door. Special wall mounted switch for control of supply to water heater shall be similarly mounted. Switches for lighting and fans inside a room shall be mounted inside the room on the side of the door nearest to the door catch, handle knob or lock approximately 150mm from the door frame.


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Section 5.2 Current Ratings Current Ratings for single core and multicore cables to be adopted for use in consumer’s installation are set out in tables 2, 3, 4 and 5 (Appendix IV) of OES4. The current carried by the cables at any time shall not exceed the specified ratings. Section 5.4 Protection against damage All conductors and cables shall be adequately protected against any risk of mechanical damage to which they may be liable in normal condition of service. Where cables pass through hole in metal works, rubbers or plastic grummets or bushes shall be provided of the edge lined with soft material to prevent abrasion of the cables. Section 5.18 Flexible cord and cables Current ratings for flexible cords and cables are set out in Table 1 (Appendix IV) of OES4. Where the apparatus requires to be earthed, flexible with earth core shall be used. Where the flexible cables and cords are exposed to the risk of mechanical damage, they shall as a minimum be sheathed with PVC or rubber and where necessary shall be armored, the armour not being used as sole means of providing earth continuity. Flexible cords and cables shall be connected to plugs, ceiling roses and movable apparatus with the BROWN core to phase, BLUE core to neutral and GREEN/YELLOW core to earth terminal of accessory or frame of the apparatus. In situations where high temperatures are encountered, flexible cables and cords shall be insulated with silicon rubber type E12 of BS6899/IEC540 Where a flexible cord supports or partially supports a luminaire, the maximum mass supported by the cord shall not exceed the values given in Table 1 (Appendix IV)


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Section 5.19 Colour identification of cable cores a. Colour identification of insulated cable cores for fixed installation and of sleeve, band or disc for bare conductors shall be as follows: - earthing conductor

green and yellow

- phase of a.c. single phase circuit

red

- neutral of a.c.single phase or three phase circuit black - phase R of three phase a.c. circuit

red

- phase Y of three phase a.c. circuit

yellow

- phase B of three phase a.c. circuit

blue

- positive of d.c. 2 wire

red

- negative of d.c. 2 wire

black

b. Colour identification of flexible cables and flexible cords shall be as follows: - live

brown

- neutral

blue

- earthing

green and yellow

Mounting Heights of Accessories Item

Height from finished floor level

Lighting Switch

1250 mm

Ceiling Fan Regulator

1250 mm

20Amp, D.P switch for water heater or A/C units

1250 mm

Shaver socket outlets

1250 mm

13Amp switched socket outlet for general purpose

450 mm

13Amp switched socket

250 mm

outlet in kitchen

Cooker control unit


1000 mm

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Symbols of Electrical Accessories – (Appendix 3 of OES 4)


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Aim : To connect two lamps in parallel Objectives: 1) Knowing the OES 4 and its sections pertaining to wiring at different installations 2) Category of load as per OES 4 3) Standards pertaining to wiring of a building for a normal household consumer 4) Standard pertaining to voltage drop, current rating, parallel operation and protection against damage. 5) Practice of wiring for a normal parallel connected load for domestic application. Tools Required: 6) Electrical / Manual Driller 7) Screw Drivers 8) Hacksaw frame with Blade 9) Wire Stripper 10)

Pliers

Accessories Required: 1) PVC Conduit 2) Conduit Saddles and Screws 3) Elbow or Bend 4) Junction box 5) Lamp Holders with Lamps 6) Single pole switch 7) Miniature Circuit Breaker (MCB) 8) Earth Leakage Circuit Breaker (ELCB) 9) 15 Amps , 1 Way Terminal Box Measuring Instruments: Multi Meter for measurement of current and voltage


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Circuit Diagram:

S

L

Single Phase 240 V, 50 Hz

L1

L2

N E

Line Diagram:

Lamp 1 Distribution Board

ELCB

MCB

Switch Lamp 2


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Layout Diagram:


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List of Material: Sr. No.

Item

1

Conduit

2

Saddles

Specification

Quantity Required

Cable Red 3

Cable Black Cable Yellow and Green

4

Switch

5

Junction box

6

Elbows or Bends

7

Lamp holder

8

MCB

9

ELCB

10

Lamp1

11

Lamp2

12

Clamp meter


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Procedure: 1) Connect the items collected per the layout diagram on the work board. 2) Check the tightness of the connections. 3) Never forget to verify the tracing of the wires as per the layout diagram. 4) CHARGE THE CIRCUIT UNDER THE SUPERVISION OF TECHNICIAN. 5) Verify the live terminal at input of the ELCB using line tester. 6) Switch ON the ELCB and using line tester observe that the circuit is live and the wiring is perfect. 7) Switch on the MCB and observe that the wiring is working perfect. 8) Similarly check that the live terminal at the Lamp Holders turns Live, only on making the switch ON. 9) Note the Operation of the circuit by visual inspection and record the data in your report. 10) Note down the reading of Voltage and current in the observation table and calculate the power.


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Measurements and Calculations: Sr. No.

Condition

1

Only Lamp1 (______W,______V)

2

Only Lamp2 (______W,______V)

3

Lamp 1 and 2

Voltage (V)

Current (I)

Calculations:

Sl No

Result:

Specification

1

Lamp 1 (alone): ______W

2

Lamp 2 (alone): ______W

Voltage V

Current I

Power Consumed (P)

Write how the activity performed meets the requirements of various

sections of OES referred at the beginning of this experiment. Answer the following questions. 1. What is the use of MCB in the circuit? 2. What is the use of ELCB in the circuit? 3. By observing the Currents drawn by the circuit and bulbs, How the bulbs are connected? 4. What is the use of earth terminal in the circuit?


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5. Exercise 5: Testing Wiring Circuits GUIDELINES FOR TESTING WIRING CIRCUITS AND CERTIFICATION OF TESTING The Oman Electricity Standard, OES 4 in Section 11 guides on the testing and inspection of the electrical installation. STANDARD, OES4 Section 11.1 General Every installation and major alteration to an existing installation shall on completion and before being energized, be inspected and tested to verify compliance with MEW regulations. Section 11.2 Visual Inspection A visual inspection shall be carried out to verify if the installation is in accordance with approved drawings and the execution of the work and workmanship and the installation methods adopted meet the requirements of the MEW regulations. Section 11.3 Colour Identification It shall be verified that the correct colour identification has been adopted for all wiring and the fuses and switches are connected in the live conductors only and links or linked switches are connected in the neutral conductor. Section 11.4 Earth Continuity Test Earth continuity test shall be carried out between the consumer’s earthing terminal and the remote end earth continuity conductors. The resistance value obtained shall not exceed 0.5 ohm. Section 11.5 Insulation Resistance Test Insulation resistance test shall be carried out on the installation. For purpose of these tests large installations must be divided into groups each containing 50 outlets. A 500V DC test voltage shall be applied. The insulation resistance to the earth shall not be less than 1 mega ohm, when measured with all poles and phases of wiring connected together and switches and fuses all in place. The insulation resistance when measured between all the conductors connected to any one pole or phase of supply and in turn all conductors connected to each other pole or phase shall not be less than 1 mega ohm.


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Section 11.6 Continuity Test Test shall be made to verify the continuity of all conductors including the earth continuity conductor of every ring circuit. Section 11.7 Earth Electrode Resistance Measurement Earth Electrode Resistance Measurement shall be carried out in accordance with method described in Appendix VI. The resistance shall not exceed 50 Ohms. Additional electrodes shall be provided where necessary to obtain this value. Section 11.8 Protection Test Tests shall be carried out to verify effective and correct operation of all earth leakage circuit breakers, close excess current protection of circuit breakers and fuse links and other protective devices. Section 11.9 Completion Certificate Following the inspection and testing, a completion certificate in the attached format shall be submitted by the electrical contractor to MEW signed by contractor’s competent engineer. The installation will then be further inspected and tested by MEW inspector and if found satisfactory, the installation will be permitted to be connected to supply.


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COMPLETION CERTIFICATE (Completion certificate to be given by the Electrical Contractor and signed by Contractor’s Competent Engineer/ Supervisor):

I hereby certify that the electrical installations at:

has been completed, inspected and tested in accordance with the regulations for electrical installations issued by the Ministry of Electricity and Water, Sultanate of Oman and is now ready for connection to mains supply.

The results are given in the attached forms.

Signed: ___________________________________ Date:__________________ For and on behalf of : _____________________________________________ _______________________________________________ _______________________________________________ Address: ______________________________________________ ________________________________________________ _______________________________________________ MEW Registration No. and Date: _____________________________________


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FORM A Particulars of the installation covered by this Certificate: New Installation.

Alteration / Extension to existing installation.

Installation Drawing: It is anticipated that the installation would comprise the following: kW S. No.

Description

No. Unit

1

Light Points

2

Air conditioners

3

Fans

4

Single Phase Motors

5

Three Phase Motors

6

Water Heaters

7

Refrigerators

8

Freezers

9

Cookers

10

13 A Socket Outlets

11

Other Loads

12

…………………………………

13

…………………………………

Total

Comment (if any) on existing installation (where the certificate relates to an alteration or addition)

Signed:____________________________________ Date:_________________


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FORM B INSPECTION AND TEST REPORT 1. Compliance with drawings: 2.

Standard of Installation: Material: Workmanship:

3. Colour identification of wiring: 4. Polarity Checks: Switches: Breakers: Links: Linked Switches: 5. Resistance of Earth Continuity Conductor from remote end to main earthing point: 6. Insulation Resistance: - With all poles and phases connected together and switches, fuses and breakers all in place - With all conductor on one phase connected together and in turn all conductors connected to each other. –

Red:

–

Yellow:

–

Blue:

–

Neutral:


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7. Continuity of all Conductors

-

Red:

-

Yellow:

-

Blue:

-

Neutral:

-

Earth:

8. Continuity of earth continuity conductor in ring circuit for socket outlet.

9. Earth Electrode Resistance:

10. Earth Leakage Circuit Breakers(Residual Current Operated Type) Continuous Rating

Operating Current

(A)

(mA)

Main Subsidiary 1) 2) 11. Load Balance Red

-

Lights

-

Refrigerators

Yellow

Blue

- Air conditioners -

Freezers

-

Cooker

-

Motors

-

Water Heaters

-

13A Socket Outlet

-

Other Loads

Signed:_____________________________________ Date:_________________


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Objectives: At the end of the exercise the student should be able to understand the following: 1) Understanding the need for Testing and Inspection of wiring in electrical installations 2) Understanding the different types of Testing and Inspection procedures as per OES 4 3) Preparing ‘Completion Certificate’ pertaining to Testing and Inspection of electrical wiring as per OES 4 4) Inspection & Testing procedure required to follow as per OES 4, for a given electrical circuit. Aim : To Connect a 3 Pin Plug connection and perform following tests 1) Visual inspection 2) Color Identification 3) Earth Continuity Test 4) Continuity Test and 5) Protection Test Tools Required: 1) Electrical / Manual Driller 2) Screw Drivers 3) Hacksaw frame with Blade 4) Wire Stripper 5) Pliers 6) Line Tester Accessories Required: 1) Conduits 2) Conduit Saddles and Screws 3) Elbow or Bend 4) Red, Black and Yellow/ Green Cable 5) Junction box 6) 3 Pin Plugs with Switches 7) Miniature Circuit Breaker (MCB) 8) Earth Leakage Circuit Breaker (ELCB) 9) 15 Amps , 1 Way Terminal Block


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Measuring Instruments: Multi Meter (KYORITSU KEW SNAP 2017)


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Circuit Diagram:

Single Phase 240 V, 50 Hz AC Supply

Line Diagram:

Distribution Board

MCB 1 ELCB

Switch Socket Outlet 1 MCB 2 Switch Socket Outlet 2


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Layout Diagram:


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List of Material: Sr. No.

Item

1

Conduit

2

Saddles

3

Elbows or Bends

Specification

Quantity Required

Cable Red 4

Cable Black Cable Yellow and Green

5

Switch Socket Unit

6

Junction box

7

Terminal Box

8

MCB

9

ELCB

10

Clamp meter


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Procedure: Visual Inspection Test: Observe the following points in this test and write observations. 1. The installation is as per the layout diagram. 2. The installation comprises of the protection devices as shown in the line diagram. 3. Accessories used are of standard quality and note down the standards printed (if any) 4. Connections and joints of the cable are firm/ tight and appropriately insulated. 5. Cables are protected against mechanical damage. 6. Switches are mounted at a minimum height of 1250 mm from finished ground surface.

Colour Identification: Observe that appropriate colour code is used in the electrical installation. Write the observations below, 1. Colour of the cable used for Live/ phase wire:__________________ 2. Colour of the cable used for Neutral wire: _____________________ 3. Colour of the cable used for Earth wire: _______________________

Earth Continuity Test: Write observation in the table below. Sr. No.

Connection of the multimeter

1

Earth terminal of Socket Outlet 1 and Earth terminal of the Distribution board

2

Earth terminal of Socket Outlet 2 and Earth terminal of the Distribution board

Observation Sound Resistance


Comment

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Continuity Test: Sr. No.

Connection of meter

1

Line terminal of outlet 1 and Line terminal of outlet 2

2

Neutral terminal of outlet 1 and Neutral terminal of outlet 2

3

Line terminal of outlet 1 and Line terminal of Distribution Box

4

Neutral terminal of outlet 1 and Neutral terminal of Distribution Box

5

Line terminal of outlet 1 and Earth terminal of Distribution Box

6

Neutral terminal of outlet 1 and Earth terminal of Distribution Box

Observation Sound

Resistance

Comment

Protection Test: Press the test button of the ELCB and note your observation:


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Answer the following questions 1. What is Visual Electrical Inspection? 2. Explain color identification procedure for electrical installation 3. What is Earth continuity test? 4. What should be the Insulation resistance as per OES-4? 5. What is continuity test? 6. How much should be the earth resistance as per OES -4?


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Exercise 6: Connection of Fluorescent Tube Light Objectives: At the end of the session the student should be able to, 1) Draw the circuit diagram of a single tube fluorescent lamp 2) State the function of each component in the circuit 3) State probable causes for different problems in the circuit malfunctioning Aim: To study the working principle, assemble, connect and check the fluorescent tube light. Tools Required: 1) Line Tester Accessories Required: 1) Fluorescent Tube Light 20 W 2) Tube light fitting 3) Ballast 4) Starter 5) Connecting wires

Types of lamps:


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Construction:

The fluorescent tube light consists, a sealed glass tube. The tube contains very small amount of Mercury mixed with an inert gas, typically Argon, kept under very low pressure. The tube also contains a Phosphor powder, coated along the inside of the glass.


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The tube has two electrodes, one at each end, which are connected to the electrical supply through bi-pin plugs at both ends of the tube. Ballast/ Choke:

Starter:

Circuit diagram: Starter Capacitor

Cathode

Bi-Pin Plug

Cathode

Bi-Pin Plug

Switch Ballast/ Choke

240V, AC Supply


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Features of Fluorescent Tube Light:       

require a ballast have a range of color temperatures and color rendering capabilities have low surface brightness compared to point sources have a cooler operation are more efficacious compared to incandescent ambient temperatures and convection currents can affect light output and life all fixtures installed indoors must use a Class P ballast that disconnects the ballast in the event it begins to overheat; high ballast operating temperatures can shorten ballast life  have options for starting methods and lamp current loadings  require compatibility with ballast  low temperatures can affect starting unless a "cold weather" ballast is specified

Working of the Fluorescent Tube Light Circuit: The electrical circuit is connected to an alternating current (AC) supply of 240V, 50 Hz. When the switch is turned ON, the path of least resistance is through the bypass circuit, and across the starter switch. In this circuit, the current passes through the electrodes on both ends of the tube. These electrodes are simple filaments, like you would find in an incandescent light bulb. When the current runs through the bypass circuit, electricity heats up the filaments. This boils off electrons from the metal surface, sending them into the gas tube, ionizing the gas.


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At the same time, the electrical current sets off an interesting sequence of events in the starter switch. The conventional starter switch is a small discharge bulb, containing neon or some other gas. The bulb has two electrodes positioned right next to each other. When electricity is initially passed through the bypass circuit, an electrical arc (essentially, a flow of charged particles) jumps between these electrodes to make a connection. This arc lights the bulb in the same way a larger arc lights a fluorescent bulb

One of the electrodes is a bimetallic strip that bends when it is heated. The small amount of heat from the lit bulb bends the bimetallic strip so it makes contact with the other electrode. With the two electrodes touching each other, the current doesn't need to jump as an arc anymore. Consequently, there are no charged particles flowing through the gas, and the light goes out. Without the heat from the light, the bimetallic strip cools, bending away from the other electrode. This opens the circuit. By the time this happens, the filaments have already ionized the gas in the fluorescent tube, creating an electrically conductive medium. The tube just needs a voltage kick across the electrodes to establish an electrical arc. This kick is provided by the lamp's ballast , a special sort of transformer wired into the circuit.


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When the current flows through the bypass circuit, it establishes a magnetic field in part of the ballast. This magnetic field is maintained by the flowing current. When the starter switch is opened, the current is briefly cut off from the ballast. The magnetic field collapses, which creates a sudden jump in current and the ballast releases its stored energy. Now the tube light becomes switched ON. Procedure: 1) Connect circuit as per the diagram. 2) Energize the circuit with 240V, 50 Hz single phase power supply. 3) Check Whether Light is glowing properly. 4) Switch off the supply and dismantle the circuit.


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Troubleshooting of Fluorescent Tube Light Circuit: Problem Possible Cause Solution Replace with new fluorescent tube Burnt-out tube. of correct dimensions and wattage Replace starter with new one of Defective Starter appropriate wattage Defective Ballast, Sometimes accompanied Replace ballast with new one of smell of burnt appropriate wattage Lamp will with insulation not glow Defective Switch Replace Switch Turn the tube and insert both the Tube not fixed correctly in bi-pin plugs into the socket the sockets correctly Check availability of power and No power to lamp continuity Replace Tube. If the lamp has been Defective Tube flashing ON and OFF repeatedly for Lamp glows long time, also replace Starter. dim Replace starter with new one of Defective Starter appropriate wattage Wiring incorrect Check wiring Replace starter with new one of Tube lit at Shorted Starter appropriate wattage the ends but middle part Replace with new fluorescent tube Tube Burnt-out is dim or of correct dimensions and wattage dark Replace ballast with new one of Wrong Ballast appropriate wattage Replace with new fluorescent tube Lamp Defective tube of correct dimensions and wattage Flashes On and also replace Starter and OFF Replace starter with new one of repeatedly Defective Starter appropriate wattage

Observations: Specifications printed on ballast: --------------------------Specifications printed on the Fluorescent Tube: -------------------Specifications printed on the Starter: ----------------------------------Voltage of the electrical supply: _________________ Current taken by the circuit from supply: ____________ Power (P) measured: __________________ Power factor of the Fluorescent Tube circuit (calculate): _________________


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Layout Diagram:

Result: The tube light connections were made and checked as per the circuit diagram. Answer the following questions. 1. What do you understand by power factor? 2. Which kind of circuit is your fluorescent lamp circuit? 3. What is the power factor of the circuit? 4. How can you improve the power factor of such a circuit? 5. If the power factor will improve. What will happen to the total power consumed? 6. Current drawn by this lamp circuit?


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Exercise 7: Sodium Vapor Lamps Objectives: At the end of the session the student should be able to: 1) Understand the working principle of Sodium Vapor Lamps 2) Analyse the differences between types of Sodium Vapor Lamps 3) Able to compare the different types of Vapor Lamps 4) Understand the connection of Sodium Vapor Lamps Aim: To assemble, connect and check the High pressure Sodium Vapor Lamp, low pressure sodium vapor lamp and also study the working principle. Accessories required: Module AZ-143a: High Pressure Sodium vapor lamp with diffusing bulb of 230 V, 150 W, lamp socket E 40 Module AZ-143b: High Pressure Sodium vapor lamp with transparent bulb of 230 V, 150 W, lamp socket E 40 Module AZ-143c: Ballast for High Pressure Sodium vapor lamp of 230 V, 150 W power factor correction capacitor of 20 μF Module AZ-144a: Low Pressure Sodium vapor lamp of clear glass with coat reflecting infrared rays - 230 V, 35 W, lamp socket BY 22d Module AZ-144b: Ballast for Low Pressure Sodium vapor lamp of 230 V, 35 W, power factor correction capacitor of 20 μF Theory: A sodium vapor lamp is a gas discharge lamp which uses sodium in an excited state to produce light. There are two varieties of such lamps: low pressure and high pressure. Low Pressure Sodium (LPS) Vapor Lamp

Low-pressure sodium (LPS) vapor lamps, also known as sodium oxide (SOX) lamps, consist of an outer vacuum envelope of glass coated with an infrared reflecting layer of indium tin oxide, a semiconductor material which allows visible light wavelengths to pass and reflects infrared back, keeping it from escaping. It has an inner


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borosilicate glass U-pipe (arc tube) containing solid sodium and a small amount of neon and argon gas mixture to start the gas discharge, so when the lamp is turned on it emits a dim red/pink light to warm the sodium metal and within few minutes it turns into the common bright yellow as the sodium metal vaporizes. LPS lamps are the most efficient electrically-powered light source when measured for photopic lighting conditions up to 200 lm/W, primarily because the output is light at a wavelength near the peak sensitivity of the human eye. As a result they are widely used for outdoor lighting such as street lights and security lighting where faithful color rendition is considered unimportant.   

LPS lamps are available with power ratings from 10 W up to 180 W; however, longer bulb lengths create design and engineering problems. LPS lamps, however, do increase energy usage slightly (about 10%) towards their end of life, which is generally around 18,000 hours for modern lamps. Because they have neither a starting electrode or an ignitor, Low Pressure Sodium Lamps require an open circuit voltage of approximately three to seven times the lamp voltage to start and sustain the lamp.

Advantages of Low-pressure sodium (LPS) lamps: 

Very efficient lamp  Powerful lamp for use of large areas  Despite a warm up time of 5-10 minutes it restarts immediately if there is a brownout  Lumen output does not drop with age (such as in LEDs or incandescent) Disadvantages of Low-pressure sodium (LPS) lamps: 

Worst color rendering of any lamp  Sodium is a hazardous material which can combust when exposed to air (such as if the bulb is broken in the trash)


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High Pressure Sodium (HPS) Vapor Lamp High-pressure sodium (HPS) lamps are smaller and contain additional elements such as mercury, and produce a dark pink glow when first struck, and a pinkish orange light when warmed. Some bulbs also briefly produce a pure to bluish white light in between. This is probably from the mercury glowing before the sodium is completely warmed. The Sodium discharge is the main source of light from the HPS lamp, and it is extremely pressure broadened by the high sodium pressures in the lamp; due to this broadening and the emissions from mercury, colors of objects under these lamps can be distinguished. This leads them to be used in areas where good color rendering is important, or desired such as streetlights and security lighting. HPS Lamps are favored by indoor growers (horticulture) for general growing because of the wide color-temperature spectrum produced and the relatively efficient cost of running the lights. High pressure sodium lamps are quite efficient about 100 lm/W when measured for photopic lighting conditions. Understanding the change in human color vision sensitivity from photopic to mesopic and scotopic is essential for proper planning when designing lighting for roads. Construction of the High Pressure Sodium Vapour Lamp:

Because of the extremely high chemical activity of the high pressure sodium arc, the arc tube is typically made of translucent Aluminum Oxide. Xenon at a low pressure is used as a "starter gas" in the HPS lamp. It has the lowest thermal conductivity and lowest ionization potential of all the non-radioactive noble gases. As a noble gas, it does not interfere with the chemical reactions occurring in the operating lamp.


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The low thermal conductivity minimizes thermal losses in the lamp while in the operating state, and the low ionization potential causes the breakdown voltage of the gas to be relatively low in the cold state, which allows the lamp to be easily started. High Pressure Sodium vapor lamps have no starting electrodes. In addition to an open circuit voltage of approximately two times the lamp voltage, these lamps are started by a high voltage starting pulse, provided by an ignitor, applied across the arc tube. Advantages of High-pressure sodium (HPS) lamps: 

Good efficiency (lumens per watt)



Smaller size than LPS or fluorescent, the HPS fits into many fixture types



Can be retrofitted into older Mercury Vapor fixtures



Better bulb life than LPS lamps

Disadvantages of High-pressure sodium (HPS) lamps:



Still has a bad color rendering compared to metal halide and halogen lamps



Requires a lossy ballast (inefficient) that operates a low arc voltage of 52100V. This reduces the actual efficiency of the lamp when you count the whole system together.

Properties of discharge lamps Ratings Maximum light output Range Efficacy Range Approximate lamp life Color of Light CRI Color Rendering Index Warm up time Re-strike time

Low pressure sodium vapor lamp 18 W to 180 W

High pressure sodium vapor lamp 35 W to 1000 W

70000 Lumens

150000 lumens

50000 lumens

80-180 lm/W

50-140 lm/W

14000 h -18000 h

16000 h -24000 h

Yellow

White

25-60 lm/W 16000 h – 24000 h White

0

25

15-55

7 -10 minutes 3 -12 seconds

3- 4 minutes 0.5 - 1 minute

5 -7 minutes 3 – 6 minutes


Mercury Vapor lamp 50 W to 1000 W

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Circuit diagram: Connection of Low Pressure Sodium Lamp:

Connection of High Pressure Sodium Lamp:


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Procedure: 1) Connect circuit as per the diagram. 2) After giving connection energize the circuit with 240V, 50 Hz single phase power supply. 3) Check Whether Light is glowing properly. 4) Switch off the supply and disconnect the circuit. Observation: Write your observation

Quantity

Low Pressure Sodium Vapor Lamp

High Pressure Sodium Vapor Lamp

Voltage

Current

Power Consumed

Warm-up time

Restrike Time

Result: Write your observation Discussion questions: 1. What are the differences between Low pressure and High pressure Sodium Vapor Lamps? 2. What is the need for Ballast in Sodium Vapor Lamp? 3. What is the need for Ignitor in High pressure Sodium Vapor Lamp? 4. Give the applications of Sodium Vapor Lamps.


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Exercise 8: Connection and Trouble Shooting of Fan Circuit Objective: 1) To identify components of Fan motor 2) To understand the principle of working and controlling the Fan motor 3) To recognize possible faults and troubleshooting of the Fan circuit Aim: 1) To identify components of Fan motor 2) To understand the principle of working and controlling the Fan motor 3) To recognize possible faults and troubleshooting of the Fan circuit Accessories Required: 1) Motor body Stator and Rotor 2) Cap and cover 3) Housing. 4) Capacitor 5) Terminal Connecter 6) Hanging bolt rod, pin, bobbin. 7) Fan blades 8) Wire guards 9) Speed regulator Theory: Fan is an electrical load which contains single phase induction motor, speed variation resisters, and capacitor etc. We know, that if a single phase induction motor is energized with single phase supply then the resultant torque produced by it will be equal to zero. So the motor does not have self starting torque. To overcome this drawback and make the motor self starting, the motor is temporarily converted into a two phase motor during starting period. For this purpose the stator of a single phase motor is provided with an extra winding which is called as starting or auxiliary winding in addition to the main or running winding. The two windings are spaced 900 electrically apart from each other and connected in parallel across single phase ac supply. The phase difference between currents flowing through the two windings is kept large (ideally 900) just as two phase currents to produce rotating magnetic field and make the motor self-starting.


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Fan motor is generally Permanent Split Capacitor (PSC) Induction Motor.

Ceiling Fan Assembly:

A A B C D E

Yoke Motor Cover Bearing Rotor Stator


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Speed Control of Fan: Fan Speed Regulator

1 OFF

2

3

4 O

L

240 V, 50 Hz, AC Supply

N

VRegulator

VFan VSupply


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Troubleshooting Split Phase Induction Motors: Tight or worn bearings: Tight or worn bearings may be due to the lubricating system failing, or when new bearings are installed, they may run hot if the shaft is not kept well oiled. If the bearings are worn to such an extent that they allow the rotor to drag on the stator, this will usually prevent the rotor from starting. The inside of the stator laminations will be worn bright where they are rubbed by the rotor. When this condition exists, it can generally be easily detected by close observation of the stator field and rotor surface when the rotor is removed. Bent shaft and bearings out of alignment: A bent rotor shaft will usually cause the rotor to bind in a certain position but then run freely until it comes bac k to the same position again. Test for a bent shaft by placing the rotor between centers on a lathe and turning the rotor slowly while a tool or marker is held in the tool post close to the surface of the rotor. If the rotor wobbles, it is an indication of a bent shaft. Bearings out of alignment are usually caused by uneven tightening of the end-shield plates. When placing end shields or brackets on a motor, tighten the bolts alternately, first drawing up two bolts, which are diametrically opposite. Open circuits and defective centrifugal switches: Open circuits in either the starting or running winding will prevent the motor from starting. This fault can be detected by testing in series with the start and finish of each winding with a test lamp or ohmmeter. A defective centrifugal switch is generally caused by dirt, grit, or some other foreign matter getting into the switch. The switch should be thoroughly cleaned with a degreasing solution and then inspected for weak or broken springs. If the winding is on the rotor, the brushes sometimes stick in the holders and fail to make good contact with the slip rings. This causes sparking at the brushes. There will probably also be a certain place where the rotor will not start until it is moved far enough for the brush to make contact on the ring. The brush holders should be cleaned and the brushes carefully fitted so they move more freely with a minimum of friction between the brush and the holders. Reversed connections and grounds: Reversed connections are caused by improperly connecting a coil or group of coils. The wrong connections can be found and corrected by making a careful check on the connections and reconnecting those that are found at fault. The compass test with a DC power source can also be used for locating reversed coils. Test the starting and running windings separately, exciting only one winding at a time, with direct current. The compass should show alternate poles around the winding. The operation of a motor that has a ground in the winding will depend on where the ground is and whether or not the frame is grounded. If the frame is grounded, then when the ground occurs in the winding, it will usually blow a fuse or trip the over-current protective device. A test for grounds can be made with a test lamp or continuity tester. One test lead should be placed on the frame and the other on a lead to the winding. If there is


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no ground, the lamp will not light, nor will any deflection be present when a meter is used. If the lamp does light or the meter shows continuity, it indicates a ground is present due to a defect somewhere in the motor’s insulation. Short circuits: Short circuits between any two windings can be detected by the use of a test lamp or continuity tester. Place one of the test leads on one wire of the starting winding and the other test lead on the wire of the running winding. If these windings are properly insulated from each other, the lamp should not light. If it does, it is a certain indication that a short or ground fault exists between the windings. Such a condition will usually cause part of the starting winding to burn out. The starting winding is always wound on top of the running winding, so a defective starting winding can be conveniently removed and replaced without disturbing the running winding. Procedure: 1. Collect the necessary items like fan, regulator, PVC conduit, saddles, screws, screw drivers, drilling machine and wires required for doing fan experiment. 2. Measure the conduit and wires as per the requirement and cut it. Fix the conduit over the work board with the help of saddles and screws. 3. Take the red wire and connect to the one end if the regulator and take the other end and connect it to the fan’s line terminal. 4. Take the black wire and connect it from the fan’s neutral point to the supply neutral point. 5. Now energize the fan circuit with the help of single phase 240 V, 50 Hz supply. 6. Now vary the speed of the fan by using conventional regulator. Connection Diagram: Complete the connection diagram


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Observations: 1. If regulator is kept in maximum resistance position then part of the input supply will be dropped across the regulator and remaining will be applied across the fan so the fan will run slowly. 2. If regulator is kept in medium resistance position then part of the input supply less than the previous one will be dropped across the regulator and remaining will be applied across the fan so the fan will run at moderate speed. 3. If regulator is kept in minimum resistance position then very less input supply will be dropped across the regulator and remaining will be applied across the fan so the fan will run at maximum speed.

Sr. No. 1

2

3

Connection of Multimeter Red and Black Wire of fan motor White and Black Wire of fan motor Red and White Wire of fan motor

Resistance Value

Sr. No.

Voltage

1

0V

2

25 V

3

50 V

4

75 V

5

100 V

6

125 V

7

150 V

8

175 V

9

200 V

10

225 V

11

250 V

Speed

Conclusions: Write your conclusion from above observations.


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ANSWER THE FOLLOWING QUESTIONS 1. What happens if the connection terminals of are interchanged? 2. Mention any two problems arise in home regarding the fan? 3. What is the Maximum speed in rpm of the fan used in the circuit? 4. Why two windings of the fan circuit connected in perpendicular? 5. What is the use of Capacitor in the fan equivalent circuit.


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Exercise 9: Metal Halide Lamps Objective: To conduct an experiment on the given Metal Halide lamp to record the power consumed and Power factor of this lighting load, operating at laboratory conditions.

Apparatus Required: 1) 2) 3) 4)

Metal Halide Lamps Ballast Ignitor Connecting Patch codes

Construction Features & Working of Metal Halide Lamps


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Metal halide (MH) lamps consist of an arc tube (also called a discharge tube or "burner") within an outer envelope, or bulb. The arc tube may be made of either quartz or ceramic and contains a starting gas (usually argon), mercury, and MH salts (Bromides or Iodides of Sodium/ Scandium/ Thallium/ Indium/ Holmium/ Thulium). Traditional quartz MH arc tubes are similar in shape to mercury vapor (MV) arc tubes, but they operate at higher temperatures and pressures .Inside the fused quartz arc tube two tungsten electrodes doped with thorium, are sealed into each end and current is passed to them by molybdenum foil seals in the fused silica. The ends of the arc tube are often externally coated with white infrared reflective zirconium silicate or zirconium oxide to reflect heat back onto the electrodes to keep them hot and thermionicaly emitting MH lamps start when their ballast supplies a high starting voltage higher than those normally supplied to the lamp electrodes through a gas mixture in the arc tube. The gas in the MH arc tube must be ionized before current can flow and start the lamp. In addition to supplying the correct starting voltage, the ballast also regulates the lamp starting current and lamp operating current . As pressure and temperature increase, the materials within the arc tube vaporize and emit light and ultraviolet (UV) radiation. A bulb (also called "outer jacket" or "outer envelope"), usually made of borosilicate glass, provides a stable thermal environment for the arc tube, contains an inert atmosphere that keeps the components of the arc tube from oxidizing at high temperatures, and reduces the amount of UV radiation that the lamp emits. Some MH lamps have a coated finish on the inside of the bulb that diffuses the light. Often a phosphor coat is used to both diffuse the light and change the lamp's colour properties. Connection Diagram


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Electrical Skills Lab Manual

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