Electrical Design Manual: Metropolitan Water District Of Southern California

MWD METROPOLITAN WATER DISTRICT OF SOUTHERN CALIFORNIA ENGINEERING SERVICES SECTION

ELECTRICAL DESIGN MANUAL

ESD-106

JANUARY 2006

TABLE OF CONTENTS

MWD Electrical Design Manual

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CHAPTER 1

PAGE

INTRODUCTION...................................................................... 1-1 1.1 1.2 1.3

1.4 2

TITLE

OBJECTIVE................................................................... 1-1 RESPONSIBILITIES OF THE ELECTRICAL DESIGNER.................................................................... 1-1 DESIGN TASKS ............................................................ 1-2 1.3.1 Study Phase ..................................................... 1-2 1.3.2 Preliminary Design Tasks ................................. 1-2 1.3.3 Final Design Tasks (30%)...................................1-2 1.3.4 Final Design Tasks (60%)...................................1-3 1.3.5 Final Design Tasks (90%)...................................1-3 1.3.6 Final Design Tasks (100%).................................1-4 DOCUMENT CONTROL ............................................... 1-4

PROJECT DESIGN ELEMENTS ............................................. 2-1 2.1

2.2

2.3

GENERAL APPROACH ................................................ 2-1 2.1.1 Design Criteria .................................................. 2-1 2.1.2 Drawings........................................................... 2-1 2.1.3 Specifications.................................................... 2-1 BASIC ELECTRICAL ENGINEERING FORMULAS ...... 2-2 2.2.1 List of Symbols ................................................. 2-2 2.2.2 Direct Current (dc) Formulas ............................ 2-2 2.2.3 Alternating Current (ac), Single Phase ............. 2-3 2.2.4 Alternating Current (ac), Three Phase .............. 2-3 2.2.5 Motors............................................................... 2-4 2.2.6 Power Factor Correction ................................... 2-4 DESIGN CALCULATIONS ............................................ 2-4 2.3.1 General ............................................................. 2-4 2.3.2 Load.................................................................. 2-5 2.3.3 Conductor Size, General ................................. 2-5 2.3.4 Conduit Size and Fill ......................................... 2-8 2.3.5 Motor Branch Circuit ......................................... 2-9 2.3.6 Power Factor Correction Capacitors................ 2-14 2.3.7 Transformer Primary and Secondary Conductors 2-17 2.3.8 Voltage Drop.................................................... 2-20 2.3.9 Short Circuit ..................................................... 2-23 2.3.10 Lighting ............................................................ 2-27

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TABLE OF CONTENTS CHAPTER

2.4

2.5 3


TITLE

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2.3.11 Grounding ........................................................ 2-36 DRAWINGS.................................................................. 2-36 2.4.1 General ............................................................ 2-34 2.4.2 Organization .................................................... 2-34 2.4.3 Legend............................................................. 2-37 2.4.4 Abbreviations ................................................... 2-37 2.4.5 Site Plan(s) ...................................................... 2-37 2.4.6 One-Line Diagrams.......................................... 2-38 2.4.7 Floor Plans....................................................... 2-39 2.4.8 Grounding Plan................................................ 2-40 2.4.9 Equipment Elevations ...................................... 2-40 2.4.10 Control Schematic Diagrams ........................... 2-40 2.4.11 Installation Details.............................................2-40 2.4.12 Electrical Schedules .........................................2-40 PROJECT FILES .......................................................... 2-44

STANDARD ELECTRICAL DESIGN PROCEDURES............. 3-1 3.1

3.2

3.3

3.4

3.5

GENERAL APPROACH ................................................ 3-1 3.1.1 Types of Electrical Systems.............................. 3-1 3.1.2 References ....................................................... 3-1 3.1.3 Plant Distribution Systems ................................ 3-2 3.1.4 Voltage Considerations..................................... 3-7 3.1.5 Voltage Selection.............................................. 3-8 3.1.6 Voltage Rating ....................................................3-8 3.1.7 Protection/Coordination Philosophy .................. 3-8 3.1.8 Equipment Heat Dissipation Data ................... 3-13 LOCATING ELECTRICAL EQUIPMENT ..................... 3-13 3.2.1 Equipment Rooms and Buildings.................... 3-13 3.2.2 Equipment Enclosures .................................... 3-14 SWITCHGEAR ............................................................. 3-15 3.3.1 Low Voltage ..................................................... 3-15 3.3.2 Medium Voltage (4.16 kV through 13.8 kV) ..... 3-17 TRANSFORMERS........................................................ 3-17 3.4.1 Pad-Mounted ................................................... 3-18 3.4.2 Unit Substations............................................... 3-18 3.4.3 Equipment Selection........................................ 3-20 MOTOR CONTROL EQUIPMENT ............................... 3-20 3.5.1 Low Voltage ..................................................... 3-20 3.5.2 Medium Voltage............................................... 3-25 3.5.3 Adjustable Speed Drives.................................. 3-27 3.5.4 Power Factor Correction .................................. 3-32

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3.6

3.7

3.8

3.9

3.10

3.11


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3.5.5 Control Circuit Devices .................................... 3-32 MOTORS...................................................................... 3-33 3.6.1 Basic Motor Types ........................................... 3-33 3.6.2 Design Considerations..................................... 3-33 3.6.3 Low-Voltage Single-Phase Induction Motors ... 3-39 3.6.4 Low-Voltage Three-Phase Induction Motors.............................................................. 3-39 3.6.5 Medium-Voltage Induction Motors ................... 3-39 3.6.6 Synchronous Motors........................................ 3-40 3.6.7 Direct Current Motors ...................................... 3-40 RACEWAY SYSTEMS ................................................. 3-41 3.7.1 Conduit System ............................................... 3-41 3.7.2 Conduit Identification ....................................... 3-42 3.7.3 Wireway ........................................................... 3-42 3.7.4 Cable Tray System .......................................... 3-42 3.7.5 Trench System................................................. 3-43 3.7.6 Ductbank System............................................. 3-43 CONDUCTORS ............................................................ 3-44 3.8.1 Low-Voltage Wiring Systems (600 Volts and Below) ....................... 3-44 3.8.2 Medium and High Voltage Conductors (Above 600 Volts) ............................................ 3-47 3.8.3 Splices and Terminations................................. 3-47 3.8.4 Conductor Identification ................................... 3-48 3.8.5 Conductor Installation ...................................... 3-48 JUNCTION BOXES AND PULL BOXES ...................... 3-49 3.9.1 Indoor Locations .............................................. 3-49 3.9.2 Outdoor Locations ........................................... 3-50 3.9.3 Corrosive Locations ......................................... 3-50 3.9.4 Hazardous Locations ....................................... 3-50 3.9.5 Terminal Junction Boxes.................................. 3-50 MANHOLES AND HANDHOLES.................................. 3-51 3.10.1 Handholes........................................................ 3-51 3.10.2 Manholes ......................................................... 3-52 LIGHTING SYSTEMS................................................... 3-52 3.11.1 General Illumination......................................... 3-53 3.11.2 Recommended Illumination Levels .................. 3-54 3.11.3 Lighting System Design ................................... 3-54 3.11.4 Luminaries ........................................................3-54 3.11.5 Emergency/Standby Lighting ........................... 3-57 3.11.6 Exit Signs......................................................... 3-58 3.11.7 Controls ........................................................... 3-58

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TABLE OF CONTENTS CHAPTER 3.12

3.13

3.14

3.15

3.16

4


TITLE

PAGE

LOW VOLTAGE POWER DISTRIBUTION................... 3.12.1 Voltage Selection............................................. 3.12.2 Panelboards..................................................... 3.12.3 Convenience Receptacles ............................... 3.12.4 Hazardous Area Receptacles .......................... 3.12.5 Power Receptacles.......................................... GROUNDING ............................................................... 3.13.1 General ............................................................ 3.13.2 System Grounding ........................................... 3.13.3 Grounding Electrode Systems and Grounding Grids .............................................. 3.13.4 Equipment Grounding...................................... 3.13.5 Instrumentation and Computer Grounding....... 3.13.6 Lightning Protection System Grounding .......... EMERGENCY AND STANDBY POWER SYSTEMS.... 3.14.1 General ............................................................ 3.14.2 Emergency Power Systems............................. 3.14.3 Legally Required Standby Power System........ 3.14.4 Optional Standby Systems............................... 3.14.5 Engine Generators........................................... 3.14.6 Unit Equipment ................................................ 3.14.7 Computer Power Systems ............................... SPECIAL SYSTEMS .................................................... 3.15.1 Plant Communication System.......................... 3.15.2 Fire Alarm System ........................................... ELECTRICAL TESTING ............................................... 3.16.1 General Requirements..................................... 3.16.2 Plant Electrical System .................................... 3.16.3 Medium and Low Voltage Equipment .............. 3.16.4 Conductors ...................................................... 3.16.5 Emergency/Standby Generators...................... 3.16.6 Grounding ........................................................

3-59 3-59 3-59 3-60 3-61 3-61 3-64 3-64 3-64 3-65 3-67 3-67 3-67 3-67 3-67 3-68 3-68 3-69 3-69 3-70 3-71 3-71 3-71 3-74 3-76 3-76 3-77 3-78 3-80 3-80 3-81

CONTROL SYSTEM DESIGN PROCEDURES ....................... 4-1 4.1

CONTROL PANELS ...................................................... 4.1.1 NEMA Standards .............................................. 4.1.2 Panel Design .................................................... 4.1.3 Indicating Devices............................................. 4.1.4 Switches, Pushbuttons, and Lights ................... 4.1.5 Annunciators..................................................... 4.1.6 Relays and Timers............................................

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4.2

4.3

APPENDIX A B C D E F G H

3-3 4-1 4-2 4-3

TITLE

PAGE

4.1.7 Control Panel Layout ........................................ 4-5 4.1.8 Wiring and Terminations ................................... 4-6 4.1.9 Nameplates....................................................... 4-8 4.1.10 Installation......................................................... 4-8 4.1.11 Seismic Design Requirements.......................... 4-8 FIELD WIRING .............................................................. 4-9 4.2.1 Field Signal Wiring............................................ 4-9 4.2.2 Conduit ............................................................ 4-13 4.2.3 Spare Conductors............................................ 4-14 CONTROL DEVICE INTERFACING............................. 4-14 4.3.1 Remote Terminal Unit Outputs ........................ 4-15 4.3.2 Control Panels ................................................. 4-15 4.3.3 Status Monitoring............................................. 4-16 4.3.4 Signal Convertors ............................................ 4-17 TITLE

PAGE

REFERENCES ............................................................................ A-1 ABBREVIATIONS........................................................................ B-1 SAMPLE ELECTRICAL DESIGN CRITERIA MEMO .................. C-1 ENCLOSURE TYPES ................................................................. D-1 MOTOR ENCLOSURE TYPES ................................................... E-1 MOTOR DESIGN TYPES.............................................................F-1 MOTOR TORQUE DEFINITIONS ............................................... G-1 STANDARD SPECIFICATIONS FOR THE IDENTIFICATION OF ELECTRICAL CURRENT CARRYING CONDUCTORS.............. H-1

FIGURE 2-1 2-2 2-3 2-4 2-5 3-1 3-2


TITLE

PAGE

Relation Between kVA, kW, and kvar ....................................... Impedance Diagram ................................................................. Zonal Cavity Calculations ......................................................... Calculation of Task Illumination ................................................ Example Panel Drawing ........................................................... Example Control Station Wiring................................................ NEMA Configurations of General Purpose Nonlocking Plugs and Receptacles....................................................................... Additional NEMA Configurations .............................................. Constant Speed Motor Control ................................................. Reversing Motor Control........................................................... Two-Speed Motor Control ........................................................

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TABLE OF CONTENTS CHAPTER 4-4 4-5 4-6 4-7 4-8 F-1 F-2 F-3 F-4 F-5 F-6 F-7

2-4 2-5 3-1 3-2 3-3 4-1 A

TITLE

PAGE

Incremental Valve Control ........................................................ 4-20 Open/Close Valve Control, Electric Motor Applicator ............... 4-21 Open/Close Valve Control, Hydraulic/Pneumatic Operator ...... 4-22 Variable Speed Motor Control-Single Phase ..............................4-23 Variable Speed Motor Control-Three Phase...............................4-24 Examples of Power Feeder Cable Identification for Water Treatment Plant Section ....................................................F-5 Examples of Control and Instrumentation Cable Identification for Water Treatment Plant Section ..........................F-6 Cable Identification .......................................................................F-8 Identification for a Multi-Conductor Cable.....................................F-9 Identification for a Single-Conductor Cable ..................................F-9 Typical Box Identification............................................................F-11 Typical Duck Bank Identification.................................................F-12

TABLE 2-1 2-2 2-3


TITLE

PAGE

Motor Circuit Design Data--480 Volt, Three-Phase Motors ....... 2-12 480-Volt Lighting Transformer Circuit Design Chart (75o C) ...... 2-17 Three-Phase Line-to-Line Voltage Drop for 600 V SingleConductor Cable per 10,000 A-ft ............................................... 2-21 Coefficient of Utilization Zonal Cavity Method ........................... 2-27 Candlepower Distribution Curve ................................................ 2-31 Losses in Electrical Equipment................................................... 3-8 Recommended Illumination Levels............................................ 3-45 Requirements for Fire Alarm and Detection Devices................. 3-65 Annunciator Sequences ............................................................. 4-4 Conductor Voltage Level Color Codes ....................................... F-7

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Chapter 1

INTRODUCTION



1.1 OBJECTIVE The objective of these electrical design standards is to provide a guide that can be used for Metropolitan Water District of Southern California's (Metropolitan) electrical practice. Anticipated users of this manual include the engineer/designer with limited experience, management staff, and the more experienced engineer/designer. The senior staff may find the manual useful as a training tool for subordinates. The information contained herein has been assembled from a number of sources; a list of the readily available sources is contained in Appendix A, References. These electrical design standards shall be used as the basis for all designs prepared for Metropolitan. Outlined within these standards are procedures for preparing design instructions, procedures for making most of the calculations that will be required for a design, a data table that can be used in making those calculations, drawing presentation formats, standard legend items and abbreviations, descriptions of materials to be used, and a number of informative memos. This information, used with engineering judgment in conjunction with appropriate codes, national standards, and other reference information, will provide electrical systems that are safe and electrically suited for the intended application. 1.2 RESPONSIBILITIES OF THE ELECTRICAL DESIGNER The electrical engineer/designer is responsible for all facets of a project that are related to: x Electrical energy for equipment located on the project site; x Adequate illumination in all areas; x Special electrical systems; x Conduits and conductors for power distribution and instrumentation and control (I&C) systems; x Protective and safety alarm systems; x Grounding and lightning protection systems;

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INTRODUCTION x Communication systems;


x Emergency power systems; The engineer/designer must take an active role in consulting with other members of the project team to identify the needs of his or her design and the needs of other design groups.

1.3 Design Tasks The following is a partial list of design tasks that the electrical engineer/ designer must assume responsibility for during the course of the design. 1.3.1 Study Phase x Provide electrical support for preparation of draft study. x Review electrical elements of project description in draft study. 1.3.2

Preliminary Design Tasks x Prepare the written electrical design criteria that are specific to the needs of the project. x Provide input to preparation of preliminary design report (PDR). x Define the method of electrical service. Contact the utility that will serve the site to define the interface required between the utility’s system and the site’s electrical distribution system. Obtain a copy of the electrical rates that will apply to the service. x Identify and talk to the electrical inspection authority having jurisdiction at the project site and obtain copies of any special ordinances or codes that may apply to the electrical design. x Work with the process design staff and mechanical engineers as well as other concerned design disciplines to define the electrical load that will be required on the project site and identify the electrical equipment. x Develop a preliminary one-line diagram and written narrative that describes the proposed electrical distribution system. x Prepare a preliminary electrical site plan showing the location of all major electrical equipment such as switchgear, transformers, electrical ductbanks, etc. x Perform preliminary calculations to size major electrical equipment. x Prepare a draft power system study.

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INTRODUCTION 1.3.3 Final Design Tasks (30%)


Update the electrical one-line diagram. Update the electrical site plan and sections. Update calculations for sizing of electrical equipment. Complete the power system study. Update the electrical equipment list Prepare draft electrical equipment specifications Table of Contents. x Prepare the electrical drawings required to define the electrical system to be constructed (See paragraph 2.4, Drawings). x Prepare draft schedules for panelboards, lighting fixtures, electrical boxes, manholes, conduit, cable,etc. x x x x x x

1.3.4

Final Design Tasks (60%) x x x x

x x x x

x

1.3.5

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Update the electrical one-line diagram. Update the electrical site plan and sections. Complete and stamp all electrical calculations. Update the electrical drawings required to define the electrical system to be constructed such as the power plan, lighting plan, grounding plan, communication systems, fire alarm systems, etc. Prepare the text electrical specifications required to define the electrical system to be constructed (See paragraph 2.1.3, Specifications). Update all schedules for panelboards, lighting fixtures, electrical boxes, manholes, conduit, cable, etc. Prepare draft control schematics and wiring diagrams. Review the Instrumentation and Control System Diagrams (I&CS) to verify that all equipment on the project site that must be interfaced with the electrical system has been accounted for. In addition, the I&CSs should be consulted when the control diagrams are being prepared because they define the relationships that exist between the electrical control equipment, the instrumentation system, and many of the equipment items supplied in other divisions of the text specifications. Prepare the ladder diagrams required for all panels that will be provided by the I&C supplier. These ladder diagrams should be used during the preparation of the process plans to determine the conduit and conductor requirements of the discrete control systems.

Final Design Tasks (90%)

1-3

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INTRODUCTION


x Complete the electrical one-line diagram. x Complete the electrical site plan and sections. x Complete all electrical drawings required to define the electrical system to be constructed such as the power plan, lighting plan, grounding plan, communication systems, fire alarm systems, etc. x Complete all electrical equipment lists. x Complete all text specifications for electrical equipment. x Complete all control schematics and wiring diagrams. x Complete all schedules. x Complete the coordination of process control schematic diagrams with Mechanical, I&C and SCADA design. x Complete all protection relay settings. 1.3.6

Final Design Tasks (100%) x Signoff of electrical plans and specifications.

1.4 DOCUMENT CONTROL This manual is intended to be (1) the primary technical reference resource for new employees in this discipline, and (2) the only reference guide for engineering consultants who will augment Metropolitan engineering staff. It is important that this manual be updated to keep it current and maintain its usefulness. To propose changes to this manual, follow the change control system procedure, located in ESD-171, Engineering Administration Manual.

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Chapter 2

PROJECT DESIGN ELEMENTS



2.1 GENERAL APPROACH A design project can be broken down into a number of specific elements that are prepared during several phases of the project. The two project phases that are being covered by this design manual are the preliminary design and final design phases. During the preliminary design phase, the needs of the project must be evaluated, a preliminary one-line diagram and electrical site plan prepared, the needs of the project outlined in a brief report, and the design criteria for the project prepared. The electrical drawings and text specifications are then prepared during final design using the information prepared during preliminary design as a basis for that design. All of the major decisions should be made during preliminary design. Final design is an implementation of those decisions. 2.1.1 Design Criteria The Electrical Design Criteria is a compilation of general information, specific requirements that are applicable to the project, and design instructions that shall be used by all of the design team members to assure a complete and consistent product. An example Electrical Design Criteria memo is presented in Appendix C. 2.1.2 Drawings The purpose of a design is to develop a set of instructions and rules that a contractor can use to bid the project and, if awarded the contract, build what the designer had in mind. The drawings are a part of that installation instruction set and describe the location and quantity of materials and equipment needed for the project; the text specifications describe the type and quality of materials and equipment and the quality of workmanship. See paragraph 2.4, Drawings, for a description of the drawings to be included in a construction package. 2.1.3 Specifications The text specifications shall describe the materials to be furnished by the contractor and the requirements for the products themselves, the requirements for installing the products, and the quality control measures that will be used to check the products and the execution of construction. Moreover, the text specifications provide these descriptions in one place for the general contractor's comprehension and use. As an electrical engineer/designer, one may think that the electrical text specifications are written for the electrical contractor, subcontractor, or equipment supplier, but this is not the case. The text specifications are addressed to the general contractor, who decides who shall do the work.

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2.1.3.1 Organization. The electrical text specifications will be prepared in Construction Specifications Institute (CSI) narrative format in the indicative mood. The standard electrical text specifications will consist of sections organized as shown in Metropolitan's ESD-135, Standard Specifications Sections Catalog. 2.1.3.2 Standard Specifications. The Standard Master Specifications have been prepared to cover all normal projects that are expected to be designed for or by Metropolitan. It is intended that the engineer will select only those text specification sections that are applicable to the project and then use those sections without changes. 2.1.3.3 Project Specifications. The engineer shall prepare project specifications in the CSI narrative format for any additional requirements not covered by the Standard Master Specifications. These specifications shall also be prepared in the indicative mood. Only three parts will be provided for in each technical section: x x x

Part 1--General; Part 2--Products; Part 3--Execution.

2.2

BASIC ELECTRICAL ENGINEERING FORMULAS

2.2.1

List of Symbols E I R X Z P VA W ș ĭ Eff

= voltage (volts) = current (amps) = resistance (ohms) = reactance (ohms) = impedance (ohms) = power (watts) = voltampere = watt = angle whose cosine is the power factor = phase = efficiency

2.2.2 Direct Current (dc) Formulas Basic formulas for dc current include: Voltage (E) = Current (I) x Resistance (R) Power (P) = E2/R = EI

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(Eq. 2-1) (Eq. 2-2)

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P = I2 x R 2.2.3

(Eq. 2-3)

Alternating Current (ac), Single Phase

Basic formulas for ac current, single phase, include: Voltage (E) = Current (I) x Impedance (Z) Power factor (PF) = cosș Apparent Power (VA) = E x I Reactive Power (vars) = E x I x sinș Real Power (Watts) = E x I x PF ș = arctan (vars/Watts) PF = Watts/(E x I) = Watts/VA

(Eq. 2-4) (Eq. 2-5) (Eq. 2-6) (Eq. 2-7) (Eq. 2-8) (Eq. 2-9) (Eq. 2-10)

The voltage drop formula is: Ed = 2 x (I x R x cosș) + (I x X x sinș)

(Eq. 2-11)

where: Ed sin ș X

= voltage drop in circuit = load reactive factor = line reactance for one conductor, in ohms

2.2.4 Alternating Current (AC), Three Phase Basic formulas for ac current, three phase, include: Line Voltage (E) = 31/2 x Eĭ (Wye-connected) Current (I) = 31/2 x Iĭ (Delta-connected) Apparent Power (kVA) = (31/2 x E x I)/1000 Real Power (kW) = kVA x cosș Reactive Power (kvar) = kVA x sinș ș = arctan (kvar/kW) Power Factor (PF) = cosș = kW/kVA PF = kW/((E x I x 31/2)/ 1000)

(Eq. 2-12) (Eq. 2-13) (Eq. 2-14) (Eq. 2-15) (Eq. 2-16) (Eq. 2-17) (Eq. 2-18) (Eq. 2-19)

The voltage drop formula is: Ed

= 31/2 x (I x R x cosș + I x X x sinș)

(Eq. 2-20)

where: Ed = voltage drop in circuit sinș = load reactive factor

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PROJECT DESIGN ELEMENTS X R


= line reactance for one conductor in ohms = line resistance for one conductor in ohms

2.2.5 Motors Motor (general) formulas include: 1 horsepower (hp) = 746 Watts Torque (ft-lb) = (hp x 5250)/rpm Fan hp = (cfm x Pressure)/(33,000 x Eff) Pump hp = (gpm x Head x Specific Gravity)/(3960 x Eff)

(Eq. 2-21) (Eq. 2-22) (Eq. 2-23) (Eq. 2-24)

Motor (single phase) formula is: Horsepower = (E x I x Eff x PF)/746

(Eq. 2-25)

Motor (three phase) formulas include: Synchronous Speed: ns = (120)(Frequency)/(# Poles) Horsepower = (E x I x 31/2 x Eff x PF)/746

(Eq. 2-26) (Eq. 2-27)

2.2.6 Power Factor Correction The size of the capacitor needed to increase the power factor from PF1 to PF2 with the initial kVA given is: kvar = kVA([1-(PF1)2]1/2 - PF1/PF2[1-(PF2)2]1/2) 2.3

(Eq. 2-28)

DESIGN CALCULATIONS

2.3.1 General Electrical calculations shall be made for all projects and filed in the project notebook. They may be made either manually or by computer programs approved by Metropolitan. As a minimum, the following types of calculations shall be made where applicable and submitted to Metropolitan for review:

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Load calculations;

x

Conductor sizing;

x

Conduit sizing;

x

Motor branch circuit sizing;

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x

Power factor improvement;

x

Transformer primary and secondary circuit sizing;

x

Voltage drop;

x

Motor starting voltage dip;

x

Short circuit analysis;

x

Lighting levels;

x

Grounding in substations.

Note: All references to the National Electrical code (NEC) for calculations shown in this design manual are based on the 2005 Edition of the NEC. If computer programs are used to make the calculations, the name and version of the software, along with all input and output data, shall be included in the submittal to Metropolitan. All calculations shall be certified by the signature and stamp of a registered professional electrical engineer. 2.3.2 Load Load calculations shall be made using applicable sections of Articles 220, 430, and other sections of the NEC. The following load calculations will be used for sizing: x x x x x

Feeder conductors and protective devices; Transformers; Panelboard and switchboard main busses; Motor control center components; Service entrance devices and conductors.

Load calculations must include all loads and should be made by summing all of the loads, using appropriate diversity factors as allowed by NEC Article 220, that are connected to each panelboard, switchboard, and motor control center. The loads for each branch of the distribution system can then be summed back to the service entrance equipment. 2.3.3 Conductor Size, General Conductor sizes must be determined for general purpose branch circuit

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conductors and feeder conductors in accordance with the requirements of NEC Article 220, the size of service entrance conductors as covered in NEC Article 230, the size of motor branch circuit conductors as covered in NEC Article 430, the size of air conditioning equipment branch circuit conductors as covered in NEC Article 440, the size of generator conductors as covered in NEC Article 445, the size of transformer primary and secondary conductors as covered by NEC Article 450, and the size of conductors to capacitors as covered in NEC Article 460. In this section we will look at the general requirements for sizing conductors once the calculated load current is known. Paragraphs 210.19 and 215.2 of the NEC require that branch circuit and feeder conductors have an ampacity not less than the load to be served. NEC Paragraph 220.18 contains additional information relative to branch circuit loads. Once branch circuit and feeder loads have been determined using applicable sections of NEC Article 230 and other applicable articles, conductor sizes shall then be determined using Tables 310.16 through 310.20 of the NEC for conductors zero through 2,000 volts and Tables 310.67 through 310.86 of the NEC for conductors rated above 2,000 volts. The four examples presented below are based on the ampacities presented in NEC Table 310.16 as modified by the applicable correction factors for temperature and conduit fill. 2.3.3.1 Example No. 1. Conditions: Continuous load rated 37 amps served by a conduit containing only the conductors for the load, running through an area having an ambient temperature of 38o C. Conductors shall be copper with type TW insulation. Required ampacity per NEC Paragraphs 210.19 and 210.18: Ampacity required = continuous load x 125% = 37 x 1.25 or 46.25 amps A No. 6 AWG copper conductor having an ampacity of 55 amps would appear to be the correct choice. Where the ambient temperatures exceed the 30o C ambient that NEC Table 310.16 is based on, the allowable ampacity of the conductor must be corrected using the correction factors at the bottom of Table 310.16 as required by NEC Paragraph 310.10. Corrected ampacity of No. 6 conductor = 55 x correction factor (0.82) or Corrected ampacity = 55 x 0.82 = 45.1 amps

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Because an ampacity of 46.25 amps is required, this conductor is not adequate and the next larger size (or a conductor with different insulation) will need to be used. 2.3.3.2 Example No. 2. Conditions: The same load and ambient temperature as above but with six phase conductors in the same conduit. Assume that the conductors used above were No. 6 copper with RHW insulation. Corrected ampacity of No. 6 RHW = 65 x 0.88 = 57.2 amps Where more than three current carrying conductors are contained in the same raceway, the ampacity of the conductors must also be derated by the ampacity adjustment factors contained in NEC Table 310.15(B)(2)(a). Corrected ampacity of No. 6 RHW conductor = 57.2 (ampacity corrected for temperature) x 0.8 (ampacity adjustment factor) = 45.7amps Because an ampacity of 46.25 amps is required, this conductor size is not satisfactory for this application. A larger conductor or a different configuration must be used. 2.3.3.3 Example No 3. Conditions: A feeder with 200 amps of noncontinuous load and 65 amps of continuous load to be installed in conduit in a wet area with an ambient temperature of 30o C or less. Required ampacity per NEC Paragraph 215.2 = noncontinuous load + 1.25 x continuous load or 200 + 1.25 x 65 = 281.25 amps The feeder overcurrent device would be sized at 300 amps since that is the next largest standard rating (see Article 240 of the NEC). The conductor ampacity requirement can be met by either one 300 kCMIL conductor or two 1/0 conductors with RHW insulation per phase. Because the ampacity of one 300 kCMIL RHW conductor is only 285 amps, NEC Paragraph 240.4(B) must be invoked.

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2.3.3.4 Example No. 4. Conditions: The same load as used in example No. 3 but the conduit is to be installed in a dry area with an ambient temperature of 38o C. Required ampacity calculated above = 281.25 amps. Ampacity of one 300 kCMIL RHH conductor is 320 in a dry location. Correction factor for 90o C conductors in a 38o C ambient = 0.91. Corrected ampacity = 320 amps x 0.91 = 291.2 amps The results are the same as for example No. 3, so NEC Paragraph 240.4(B) must be invoked. 2.3.4 Conduit Size and Fill Where conductors are installed in conduit, the conduit shall be sized in accordance with Tables C.1 through C.12(A) in Annex C of the NEC, and all associated notes. Following are two examples of how conduits can be sized under different circumstances. 2.3.4.1 Example No. 1. Conditions: Three 4/0 AWG conductors with RHH/RHW insulation installed in rigid steel conduit (no separate ground conductor). See NEC Table 3C.8 for conduit size required for three 4/0 AWG conductors with RHH/RHW insulation. NEC Table 3C8 would allow three conductors to be installed in a 2-inch conduit. 2.3.4.2 Example No. 2. Conditions: Three No. 4/0 AWG phase conductors, one No. 1/0 AWG neutral and one No. 2 AWG equipment ground conductor to be installed in rigid steel conduit. Phase and neutral conductor insulation will be RHH/RHW and the ground conductor will have TW insulation. Because NEC Table C.8 is for situations where all conductors in a conduit are the same size, they cannot be used for this example. Table 4 in Chapter 9 of the NEC, using appropriate conduction areas from Table 5 in Chapter 9 of the NEC, must

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then be used. Total conductor area: Conductor size 4/0 RHH/RHW 1/0 RHH/RHW # 2 TW

Area 0.4754 0.3039 0.1333

Total Area = 3(0.4754) + 0.3039 + 0.1333 = 1.8634 sq.in. Conduit size required: Because more than two conductors that are not lead covered are being installed, the column for 40 percent fill in Table 4 in Chapter 9 of the NEC can be used. Select conduit with a usable area greater than 1.8634 square inches; therefore, conduit size = 2-1/2 inch (40 percent of total area = 1. 946 sq.in.)

2.3.5 Motor Branch Circuit NEC Article 430, Motors, Motor Circuits, and Controllers, covers the provisions for motors, motor circuits, and controllers. NEC Article 430 includes tables for motor full-load currents, which are the minimum values that can be used in determining sizes of motor branch circuits, motor feeders, short circuit and overcurrent device sizes and settings, and miscellaneous load calculations. Actual nameplate currents should be used if they are known and must be used if they are larger than the minimum. The full load current to be used for motors with speeds less than 1,200 rpm should be obtained from the motor manufacturer. NEC Article 440 contains special provisions that apply to the installation of airconditioning and refrigeration equipment and should be referred to for these applications. The following calculations and the accompanying table are based on the applicable provisions of NEC Article 430 and are provided as a guide for performing motor branch circuit and feeder calculations and for sizing components for motor branch circuits as part of a design. The typical calculations that are required are demonstrated by the following examples.

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2.3.5.1 Example No. 1. Conditions: Induction motor is rated 60 hp, 460 volts, three-phase, 1,800 rpm continuous, and will be powered by a combination motor starter through a conduit system. All equipment and the conduit system is located in areas with ambient temperatures of 30o C or less. In NEC Table 430.250, the motor full-load current that must be used in the calculations is 77 amps. Using this value we can size the motor branch circuit and ground fault protection device, the branch circuit conductors, and the motor disconnecting means. Motor branch circuit and ground fault protection devices are to be sized as outlined in Part IV of NEC Article 430 with maximum settings as provided in NEC Table 430.52. Actual settings should reflect the recommendation of the manufacturer of the motor control equipment that will be provided. For example, the following are General Electric's recommendations: Device type Magnetic only circuit breaker Thermal magnetic breaker Time delay fuses

Rating 100 amp 125 amp 90 amp

Branch circuit conductors shall be sized in accordance with the requirements of Part II of NEC Article 430. NEC Paragraph 430.22 requires that conductors supplying a motor must have an ampacity not less than 125 percent of the full-load current of the motor. A special exception is made for motors that are operated intermittently for short periods of time. Motor branch circuit ampacity shall be equal to or greater than: 77 amps x 1.25 = 96.25 amps Conductor size to be No. 1 AWG copper with RHH insulation No. 1 AWG = 110 amps at 60o C Note: 60o C ampacity rating of conductors No. 1 AWG and smaller must be used unless the engineer is sure that all terminals are rated for use at 75o C--see the Underwriters Laboratories, Inc. General Information Directory for more details on this subject.

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Motor disconnecting means shall be sized in accordance with the requirements of Part IX of NEC Article 430. The disconnecting means for motor circuits rated 600 volts, nominal, or less, shall have an ampere rating of at least 115 percent of the full-load current rating of the motor. Motor disconnecting means shall be sized greater than: 77 amps x 1.15 = 88.5 Disconnect to be rated 100 amps See Table 2-1 for the conduit and conductor requirements for motors typically found in design projects. 2.3.5.2 Example No. 2. Conditions: Determine the size of the feeder conductors and thermal magnetic circuit breaker feeding a motor control center that has a total connected motor load of 215 amps with the uppermost 60-hp motor being the largest motor. In addition, there are 45 amps of continuous load and 65 amps of noncontinuous load. Conductors shall be copper with type RHH/RHW insulation installed in an area where the ambient temperature is less than 30o C. Assume all motors are 460 Volt, 3 phase and 1800 rpm. Motor feeder conductors shall be sized in accordance with applicable portions of Part II of NEC Article 430 and feeder breakers shall be sized in accordance with applicable portions of Part V of NEC Article 430. NEC paragraph 430.24 requires that the conductors supplying the motor control center have an ampacity not less than 125 percent of the full-load current rating of the highest rated motor plus the sum of the full-load current ratings of all other motors in the group, as determined by Paragraph 430.6(A), plus the ampacity required for the other loads. The required ampacity of the conductors shall be calculated as follows: Total motor load + 25% of largest motor FLA + noncontinuous load + 125% of continuous load or 215 + (.25 x 77) + 65 + (1.25 x 45) = 355 amps Conductors may be either one 500 kCMIL or two No. 3/0 AWG per phase (one 500 kCMIL = 380 amps, two No. 3/0 = 400 amps).

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NEC Paragraph 430.62 covers the requirements for sizing the motor feeder short-circuit and ground-vault protection. NEC Paragraph 430.63 covers the requirements for sizing the feeder protection when the feeder supplies a motor load and other power and lighting loads.

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Table 2-1. Motor Circuit Design Data 480 Volt, Three-Phase Motors HP

Mcp Size

Starter Size

FLA

FLA *1.50

Conductor Size

Conduit Size

Max. Dist.

1/2

3/M

1

1

1.25

3#12,1#12G

3/4”

5,333

3/4

3/M

1

1.4

1.75

3#12,1#12G

3/4”

3,810

1

3/M

1

1.8

2.25

3#12,1#12G

3/4”

2,963

1-1/2

7/M

1

2.6

3.25

3#12,1#12G

3/4”

2,051

2

7/M

1

3.4

4.25

3#12,1#12G

3/4”

1,569

3

7/M

1

4.8

6.00

3#12,1#12G

3/4”

1,111

5

15/M

1

7.6

9.50

3#12,1#12G

3/4”

701

7.5

15/M

1

11

13.75

3#12,1#12G

3/4”

485

10

30/M

1

14

17.50

3#12,1#12G

3/4”

381

15

30/M

2

21

26.25

3#10,1#10G

3/4”

403

20

50/M

2

27

33.75

3#8,1#10G

1”

485

25

50/M

2

34

42.50

3#6,1#10G

1-1/4”

580

30

100/M

3

40

50.00

3#6,1#10G

1-1/4”

493

40

100/M

3

52

65.00

3#4,1#8G

1-1/4”

577

50

100/M

3

65

81.25

3#3,1#6G

1/1/2”

554

60

250/M

4

77

96.25

3#1,1#6G

2”

719

75

250/M

4

96

120

3#1,1#6G

2”

577

100

250/M

4

124

155

3#2/0,1#12G

2”

611

125

250/M

5

156

195

3#3/0,1#12G

2-1/2”

577

150

300

5

180

225

3#4/0,1#12G

2-1/2”

615

200

400

5

240

300

3#350Kcm,1#3G

3”

600

Notes:1) 2) 3) 4) 5)

6)

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Conductor ampacity is based on 60 C through size No. 1 AWG and on 75 C above size No. 1 AWG. Use thermal/magnetic circuit breakers in all autotransformer type starters. Conduit size is based on NEC Table 4 and 5, and areas are based on conductor insulation Type RHH/RHW. Conductor size is based on 125% of motor full load current. Maximum distance is based on an allowed voltage drop of 3%. These distances are calculated using Table 2-3 assuming copper conductors in rigid metal conduit and a PF of 80%. Ground conductor size (1#_G) shown in conductor size column is based on NEC Table 250-95.

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For the above example, a 400-amp device would be selected. For the 400-amp device to be used to protect the 500-kcm conductors, NEC Paragraph 240.4(B) needs to be invoked. 2.3.6 Power Factor Correction Capacitors Power factor correction capacitors are installed for either one of the following reasons: x

To increase the measured power factor at the serving utilities meter and reduce the power factor penalty being imposed by the utility. Power factor correction for this reason cannot be justified unless the serving utility actually has a power factor penalty in their rate schedule.

x

To release additional capacity in existing feeder conductors.

For example, a three-phase load of 200 kW would be equal to 301 amps at 480 volts if the power factor were 80 percent, but would be only 254 amps if the power factor were raised to 95 percent. This would release 47 amps of capacity for additional loads. Article 460 of the NEC covers the installation of capacitors on electric circuits. In this section those calculations needed to determine the size of the capacitor required and the size of conductors required to connect the capacitors to their electric power supply will be discussed. Following are several examples to illustrate the required calculations: 2.3.6.1 Example No. 1. Conditions: A load of 200 kVA exists at 480 volts with a power factor of 80 percent. Determine the amount of capacitors required to improve the power factor to 95 percent. Power factor = Real power (kW) y Apparent power (kVA)

(Eq. 2-29)

Figure 2-1 is provided to show the relation that exists between apparent power, real power, and reactive power (kvar). By definition, the power factor is the cosine of the angle that exists between the real power and apparent power phasors. The calculation to determine the amount of capacitance (measured in kvar) shall be made as follows:

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RESULTANT REACTIVE POWER (kV AR)

REAL POWER (KW)

T1 T2 RESULTANT POWER SUPPLIED BY CAPACITATORS (kV AR)

APPARENT POWER (kVA)

REQUIRED REACTIVE POWER (kV AR)

Figure 2-1. Relation Between kVA, kW, and kvar

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kvar @ initial power factor = [(kVA)2 - (kW)2 ]1/2 or [(kVA)2 - (kVA X PF)2]1/2

(Eq. 2-30) (Eq. 2-31)

kvar = [(200kVA)2 - (160kW)2]1/2 kvar = (40,000 - 25,600)1/2 = 120 kvar Because the real power of a load is not changed when the power factor is improved, we can use the known real power and desired power factor to calculate the new kvar value in the phasor triangle. kvar @ 95% power factor = [( kW y PF)2 - (kW)2] 1/2 (Eq. 2-32) kvar = [(160 y .95)2 - (160)2]1/2 kvar = (28,366 - 25,600)1/2 = 52.6 Required kvar for correction = 120 - 52.6 = 67.4 kvar Similar calculations can be made to determine the size of the capacitor required to improve the power factor of a single motor to a higher power factor, but tables are available from capacitor manufacturers to simplify the selection of these capacitors. Capacitors larger than the maximum size recommended by motor manufacturers must not be installed. 2.3.6.2 Example No. 2. Conditions: Load is a 60-hp, 1,800-rpm motor operating at 480 volts, three-phase. Capacitors rated 15 kvar at 480 volts are being installed to improve the power factor. Determine the size of the conductor needed to meet the requirements of the NEC. NEC Paragraph 460.8 contains two criteria that must be met when sizing branch circuit conductors to capacitors. First, the ampacity of the conductors must be at least 135 percent of the rated current of the capacitors. Second, if the capacitors are connected to a motor circuit, the conductors to the capacitor shall have an ampacity not less than one third of the ampacity of the motor branch circuit conductors. Capacitor rated amps = 15 y (0.48 x 1.73) = 18 Branch circuit amps = 18 x 1.35 = 24.4 minimum Motor branch circuit amps = 1.25 x 77 = 96.25 Need to use No. 1 AWG at 110 amps (60o C ampacity) Capacitor branch circuit amps as one-third of motor branch circuit conductor ampacity = 110 y 3 = 36.7 amps

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Therefore, the branch circuit conductors to the capacitor must have an ampacity of 37 amps or greater. Refer to the Industrial Power Systems Handbook by Beeman or Electrical Systems Analysis and Design for Industrial Plants by Lazar for additional formulas related to the application of capacitors on electrical systems. 2.3.7 Transformer Primary and Secondary Conductors Article 450 of the NEC, Transformers and Transformer Vaults, covers the installation of all transformers. Article 450 deals with transformers over 600 volts nominal and transformers 600 volts, nominal, and less. The calculations most often made during an electrical system design are for a transformer 600 volts, nominal, or less with both primary and secondary protection. The following calculations and Table 2-2 are based on the provisions of NEC Paragraph 450.3(B). Primary conductors and feeder overcurrent and ground fault protection devices (feeder breakers) are sized for the next larger device above 150 percent of the transformer full-load amps to minimize the possibility of the feeder breaker tripping on transformer inrush (NEC would allow breaker to be sized up to 250 percent of primary full load amps). The secondary conductors and secondary breaker are sized at the standard rating that is nearest to 125 percent of the calculated secondary full load current as required by the NEC. Note 1 to Table 450.3(B) of the NEC allows moving up to the next higher standard rating. Following are two examples to show the calculations that are required for three-phase and single-phase transformers. 2.3.7.1 Example No. 1. Conditions: Assume a 45-kVA 3-phase transformer with a 480-volt primary and a 208Y/120-volt secondary. Calculate primary full-load amps: 45 kVA y [(480 volts x 1.73) y 1000] = 54.2 amps Calculate required feeder breaker and conductor ampacity: 54.2 amps x 1.5 = 81 amps

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2-18

3

3

45

75

480

480

480

480

480

480

480

480

480

480

480

480

Volts

90

54

36

18

11

104

78

52

31

21

16

10

Amps

135.00

81.00

54.00

27.00

16.50

156.00

117.00

78.00

46.50

31.50

24.00

15.00

Ckt. Amps

2" C-3#1/0,1#6G

1 1/2" C-3# 3,1#8G

1" C-3# 6,1#8G

3/4" C-3# 10,1#8G

3/4" C-3# 12,1#8G

2" C-2#2/0,1#6G

1 1/2" C-2# 1,1#6G

1 1/4" C-2# 3,1#8G

1 1/4" C-2# 6,1#8G

1" C-2# 8,1#8G

3/4" C-2# 10,1#8G

3/4" C-2# 12,1#8G

Ckt. Conduit & Wire

Primary Circuit

150A/3P

90A/3P

60A/3P

30A/3P

20A/3P

175A/2P

125A/2P

80A/2P

50A/2P

30A/2P

25A/2P

20A/2P

Ckt. Breaker

208

208

208

208

208

240

240

240

240

240

240

240

Volts

208

125

83

42

25

208

156

104

63

42

31

21

Amps

260.00

156.25

103.75

52.50

31.25

260.00

175.00

130.00

78.75

52.50

38.75

26.25

Ckt. Amps

2 1/2" C-4# 4/0,1#2G

2 1/2" C-4# 2/0,1#4G

1 1/2" C-4# 2,1#6G

1 1/2" C-4# 6,1#8G

1" C-4# 10,1#8G

2 1/2" C-3# 4/0,1#2G

2”6,3#3/0,1#4G

2" C-3# 1,1#6G

1 1/2" C-3# 4,1#8G

1 1/2" C-3# 6,1#8G

1" C-3# 8,1#8G

3/4" C-3# 10,1#8G

Ckt. Conduit & Wire

Secondary Circuit

250A/3P

175A/3P

110A/3P

60A/3P

35A/3P

250A/2P

200A/2P

150A/2P

80A/2P

60A/2P

40A/2P

30A/2P

Ckt. Breaker

______________________________________________________________________________________________________________________________________________ Rules Used: 1) Feeder circuit breaker at next size larger than 1.5 times primary amps (NEC 450.3(b) allows up to 250% of primary amps). 2) Panel main breaker sized at next size larger than 1.25 times secondary amps. (NEC 450.3(B) allows up to next larger than 125% of sec. Amps) 3) All conductors No.1 AWG and smaller sized based on 60q C ampacities, larger conductor sizes based on 75q C ampacities. (Conductors sized per NEC 240-4 including exceptions. 4) Minimum ground conductor sized at #8; Table 250.122 used for other primary side grounds and Table 250.66 used for secondary side grounds. 5) Conduit size based on NEC Chapter 9 Table 3C. ______________________________________________________________________________________________________________________________________________

3

3

3

9

30

1

50

15

1

1

25

15

37.5

1

1

10

1

1

5

Phase

7.5

KVA

Transformer

Table 2-2. 480-Volt Lighting Transformer Circuit Design Chart (75q C)

PROJECT DESIGN ELEMENTS MWD Electrical Design Manual




Use a 90-amp breaker and No. 3 AWG copper conductors* Calculate secondary full-load amps: 45 kVA y [(208 volts x 1.73) y 1000] = 125.06 amps Calculate required secondary breaker size and conductor ampacity: 125.06 amps x 1.25 = 156.3 amps Use a 150-amp breaker and No. 1/0 copper conductors* Note: This selection limits the continuous load that can be supplied by the transformer to 43.2 kVA ((80% x 208 volts x 150 amps x 1.73) y 1000). The ground conductors for the above circuits shall be sized in accordance with NEC Tables 250.66 and 250.122. The ground conductor in the feeder to the primary shall be sized as an equipment ground in accordance with NEC Table 250.122. The grounding electrode conductor on the secondary of the transformer shall be sized as required by NEC Paragraph 250.30 using Table 250.66. 2.3.7.2 Example No. 2. Conditions: Assume a 25-kVA single-phase transformer with a 480-volt primary and a 120/240-volt secondary. Calculate primary full-load amps: 25 kVA y (480 volts y 1000) = 52.1 amps Calculate required feeder breaker size and conductor ampacity: 52.1 amps x 1.5 = 78.1 amps Use an 80-amp breaker and No. 3 AWG copper conductors* Calculate secondary full-load amps: 25 kVA y (240 volts y 1000) = 104.2 amps Calculate required secondary breaker size and conductor ampacity: 104.2 amps x 1.25 = 130 amps *

Conductor sizes for examples No. 1 and No. 2 are based on the use of 60q C wire for sizes Nos. 14 through 1 AWG and 75q C wire for sizes No. 1/0 and larger as required by the General Information Directory 1988, published by Underwriters Lab, Inc., because many items of equipment are still not rated with 75q C terminals in these sizes.

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Use a 125-amp breaker and No. 1 AWG copper conductors*. 2.3.8

Voltage Drop

2.3.8.1 Feeder and Branch Circuits. Fine-print note No. 4 to NEC Paragraph 210.19 says that branch circuit conductors must be sized so that voltage drop on the branch circuit does not exceed 3 percent. Furthermore, it states that the total voltage drop on feeder conductors plus branch circuit conductors must not exceed 5 percent. Fine-print note No. 2 to NEC Paragraph 215.2(A) would allow the voltage drop on a feeder to be 3 percent as long as the total voltage drop to the load is 5 percent or less. Steady-state voltage drops are caused by current flowing through an impedance. To calculate steady-state voltage drop, the circuit impedance, circuit current, and power factor of that current relative to some voltage must be known. Rigorous methods of calculating voltage drop can be very involved and complicated and for purposes of ordinary use in designing power circuits for industrial projects, approximate methods are generally satisfactory. IEEE Standard 141 (Red Book) gives the approximate formula for voltage drop as: V = IR cos ș + IX sin ș

(Eq. 2-33)

where: V I R X ș cos ș sin ș

= voltage drop in circuit, line to neutral = current flowing in conductor = line resistance for one conductor in ohms = line reactance for one conductor in ohms = angle whose cosine is the load power factor = load power factor in decimals = load reactive factor in decimals

The voltage drop calculated using this formula must be multiplied by 2 for single-phase circuits and 1.73 for three-phase circuits. Calculations using the above formula are not required for most designs *

Conductor sizes for examples No. 1 and No. 2 are based on the use of 60q C wire for sizes Nos. 14 through 1 AWG and 75q C wire for sizes No. 1/0 and larger as required by the General Information Directory 1988, published by Underwriters Lab, Inc., because many items of equipment are still not rated with 75q C terminals in these sizes.

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because the results obtained using published tables give satisfactory results. The following calculations were made using Table 2-3 which is a reproduction of Table 3-12 of IEEE STD 141-1993 and the procedure for making the calculations that accompanies Table 3-12. Similar results can be obtained using published tables and graphs available in other reference books and manufacturer's catalogs. 2.3.8.2 Example. Condition: No. 1 AWG copper conductors feeding a motor rated 60 hp (77 amps full-load), three-phase, 460 volts through rigid metal conduit with a circuit length of 520 feet. Assume that the motor power factor is 85 percent. Calculate voltage drop on a three-phase circuit from Table 2-3. The factor for No. 1 AWG copper conductors in magnetic conduit at 85 percent PF = 2.7 (need to interpolate between 0.8 and 0.9 PF) Voltage drop = ((520 ft x 77 amps) y 10000) x 2.7 volts drop = 10.8 volts Calculate percent voltage drop by dividing the calculated volts drop by the system voltage and then multiplying by 100: (10.8 volts y 480 volts) x 100 = 2.25 % drop Factors are provided at the bottom of Table 2-3 and are to be used to convert the calculated voltage drop to single-phase line-to-line and singlephase line-to-neutral values.

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2-22

0.33 0.50 0.55 0.62 0.66

0.55 0.76 0.82 0.88 0.92

0.51 0.67 0.71 0.76 0.78

Section 2: Copper conductors in nonmagnetic conduit 1.00 0.23 0.26 0.28 0.29 0.95 0.40 0.43 0.45 0.47 0.90 0.47 0.48 0.52 0.54 0.80 0.54 0.55 0.57 0.59 0.70 0.57 0.59 0.62 0.64

Section 3: Aluminum conductors in magnetic conduit 1.00 0.42 0.45 0.49 0.52 0.95 0.62 0.65 0.70 0.73 0.90 0.69 0.72 0.76 0.79 0.80 0.76 0.80 0.83 0.85 0.70 0.80 0.83 0.87 0.89

Section 4: Aluminum conductors in nonmagnetic conduit 1.00 0.36 0.39 0.44 0.47 0.95 0.52 0.56 0.60 0.63 0.90 0.57 0.61 0.65 0.68 0.80 0.63 0.66 0.71 0.7 0.70 0.66 0.69 0.73 0.75

*Solid conductor. Other conductors are standard.

0.42 0.64 0.71 0.80 0.83

0.37 0.59 0.66 0.74 0.80

0.70 0.85 0.89 0.92 0.92

0.74 0.94 0.99 1.0 1.1

0.45 0.62 0.68 0.73 0.74

0.50 0.71 0.78 0.85 0.88

500

0.88 1.0 1.1 1.1 1.1

0.91 1.1 1.2 1.2 1.2

0.55 0.71 0.76 0.81 0.83

0.60 0.81 0.88 0.95 0.97

400

1.2 1.3 1.3 1.3 1.3

1.2 1.4 1.4 1.4 1.4

0.73 0.92 0.95 0.97 0.97

0.78 1.0 1.1 1.1 1.1

300

1.4 1.5 1.5 1.5 1.4

1.4 1.6 1.6 1.6 1.6

0.88 1.0 1.1 1.1 1.1

0.92 1.1 1.2 1.2 1.2

250

1.7 1.8 1.8 1.7 1.6

1.7 1.8 1.9 1.8 1.7

1.0 1.1 1.1 1.1 1.1

1.1 1.3 1.3 1.4 1.3

4/0

2.1 2.2 2.2 2.1 1.7

2.1 2.3 2.3 2.2 2.1

1.3 1.5 1.5 1.4 1.4

1.4 1.5 1.6 1.6 1.5

3/0

To convert voltage drop to Single-phase, three-wire, line-to-line Single-phase, three-wire, line-to-neutral Three-phase, line-to-neutral

1.0 1.1 1.2 1.2 1.1

1.0 1.2 1.3 1.3 1.3

0.62 0.80 0.85 0.88 0.88

0.68 0.88 0.95 1.0 1.0

350

Wire size (AWG or kemil)

3.3 3.4 3.3 3.1 2.8

3.3 3.4 3.4 3.2 2.9

2.1 2.2 2.2 2.1 2.0

2.1 2.3 2.3 2.3 2.1

1/0

Multiply by 1.15 0.577 0.577

2.6 2.7 2.6 2.5 2.3

2.6 2.7 2.7 2.6 2.4

1.6 1.8 1.8 1.7 1.6

1.7 1.9 1.9 1.9 1.8

2/0

4.2 4.2 4.1 3.8 3.4

4.2 4.2 4.1 3.9 3.6

2.6 2.7 2.7 2.5 2.4

2.6 2.8 2.8 2.6 2.5

1

5.2 5.2 5.0 4.6 4.2

5.2 5.3 5.1 4.7 4.3

3.3 3.4 3.3 3.1 2.8

3.4 3.5 3.4 3.2 3.0

2

Reproduced from IEEE Std 141-1993, IEEE Recommended Practice for Electric Power Distribution for Industrial Plants, © 1994, by the Institute of Electrical and Electronics Engineers, Inc., with the permission of the IEEE.

0.59 0.74 0.79 0.83 0.83

0.63 0.83 0.88 0.95 0.98

0.38 0.54 0.59 0.66 0.69

600

700

Load Power factor Lagging 1000 900 800 750 Section 1: Copper conductors in magnetic conduit 1.00 0.28 0.31 0.34 0.35 0.95 0.50 0.52 0.55 0.57 0.90 0.57 0.59 0.62 0.64 0.80 0.66 0.68 0.71 0.73 0.70 0.71 0.73 0.76 0.78

8.4 8.2 7.9 7.2 6.4

8.4 8.2 7.9 7.3 6.5

5.3 5.3 5.1 4.7 4.3

5.3 5.3 5.2 4.8 4.4

4

13 13 12 11 9.9

13 13 12 11 10

8.4 8.2 7.9 7.2 6.4

8.4 8.2 8.0 7.3 6.6

6

21 20 19 17 15

21 20 19 17 15

13 13 12 11 9.7

13 13 12 11 9.9

8*

Table 2-3. Three-phase line-to-line voltage drop for 600 V single-conductor cable Per 10 000 A-ft (60q C conductor temperature, 60 Hz)

33 32 30 27 24

33 32 30 27 24

21 20 19 17 15

21 20 19 17 15

10*

52 50 48 42 37

52 50 48 43 37

33 32 30 27 24

33 32 30 27 24

12*

------

------

53 50 48 43 38

53 50 48 43 38

14*

PROJECT DESIGN ELEMENTS MWD Electrical Design Manual




2.3.8.3 Motor Starting. The calculations required to determine the voltage drop on an electrical system because of motor starting are too complex to be covered in this design guide. The Industrial Power Systems Handbook by Beeman and Electrical Systems Analysis and Design for Industrial Plants by Lazar both have very complete sections on this subject. These calculations are often done as part of a short circuit analysis using a computer program such as ETAP, because they are very complex and are based on much of the same information required to do the short circuit analysis. These calculations should be made based on the largest motor at each load center to determine if the voltage drop on motor starting is of such magnitude that it will cause adverse impacts on other equipment in the system. For instance, a 20 percent voltage dip could cause control relays to drop out since many of these are only designed to operate at voltage levels 10 percent below rated voltage. 2.3.9 Short Circuit The proper selection of protective devices and coordination of their trip settings is based on short circuit calculations. The calculations required to complete a detailed short circuit analysis are very complex and beyond the scope of this design guide. The Industrial Power Systems Handbook by Beeman, Electrical Systems Analysis and Design for Industrial Plants by Lazar, the IEEE Std 141-1993, and many other references contain detailed procedures for performing short circuit analysis. In those situations where an approximate value of short circuit current is needed for preliminary design purposes, the following abbreviated method can be used to determine a very conservative value. In every situation where this method is used, a detailed calculation, either made by hand or using an approved computer program, shall be made during final design. Calculations to determine an approximate value of symmetrical short circuit current in a power distribution system are shown in the following example: 2.3.9.1 Example. Conditions: The load will be served by a 1,500-kVA transformer at 480 volts three-phase through a single motor control center. The fault current available from the utility on the source side of the transformer is unknown, the transformer impedance is assumed to be 5.75 percent (based on published data), and the motor load on the transformer is approximately 75 percent of the rating of the transformer. The current flowing during a fault at any point in an electrical system is limited by the impedance of the circuits and equipment from the source or sources to the point where the fault has

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occurred. For these simplified calculations we will assume that the only sources are the transformer and the motors connected to the system. Figure 2-2 shows that the motors are connected in parallel with the transformer as impedance with an infinite bus as the source of the fault current. The basic formula used to calculate short circuit currents is: Short circuit current = volts y total impedance (ohm's law)

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(Eq. 2-34)

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A point-to-point calculation of short circuit current available at any point can be made using this formula and it is the basic formula used in the perunit method to calculate short circuit current values in electric power circuits. The reactance of the utility system must be assumed to be zero and the following simplification can be made to determine short circuit current let-through by a transformer: Approximate transformer per-unit Z = (%Z)(base kVA) y [(100) (transformer kVA)] (Eq. 2-35) If we let base kVA = transformer kVA, then: per-unit Z of the transformer = %Z / 100

(Eq. 2-36)

The basic formula for calculating short circuit current when the per-unit method is used is: Is.c. rms sym = base kVA y (1.73 x kV x (per-unit Z of the transformer)) (Eq. 2-37) Because we have let base kVA = transformer kVA and transformer kVA y (1.73 x kV) = Transformer load current for three phase transformers, we can simplify the above formula to: Is.c. rms sym = Transformer FLA y (%Z y 100)

(Eq. 2-38)

Transformer FLA = 1,500 kVA y (0.48 x 1.73) or FLA = 1,806.4 amps (Eq. 2-39) The resulting short circuit current let through by the transformer in our example would be: Is.c.rms sym = 1806.4 y (5.32* y 100) or Is.c. rms sym = 33,914 amps

*.Note:

Published transformer impedances are subject to a ±7.5 percent tolerance. To be conservative in these calculations, the lower limit of 5.32 percent (5.75 - (0.075 x 5.75)) has been used.

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The motor contribution to a fault by a single or group of low-voltage induction motors can be taken as approximately four times the motor fullload current since the reactance of a low-voltage induction motor, including the leads, is approximately 25 percent. A point-to-point calculation made as above for a transformer would result in a multiplier of 4. Motor load of 75 percent of transformer rating was given; therefore, motor FLA would be 1,806 x .75 = 1,355 amps. Is.c. rms sym = 1,355 x 4 = 5,420 amps The total short circuit current available at the point of the fault would be the total of the contribution from the transformer plus the contribution for the motor load or total Is.c. rms sym = 33,914 + 5,420 or 39,334 amps rms sym Because neither the serving utilities' source impedance nor the impedances of the interconnecting conductors and equipment are included in this calculation, this value can be very conservative and must be used carefully. 2.3.10 Lighting Lighting calculations shall be made using the recommended procedures established by the Illuminating Engineering Society and outlined in the IES Lighting Handbook. Two methods are available for calculating the lighting levels in a space. The first is the lumen or zonal cavity method and the second is the point-by-point method. The zonal cavity method is used to calculate the average footcandle level within the space and the point-bypoint method is used to predict the illumination for a specific visual task. The following examples are provided to demonstrate these two calculation methods. 2.3.10.1 Example No. 1--Lumen or Zonal Cavity Method. Conditions: Design a lighting system for a room 15 feet x 25 feet having an 11-foot ceiling that will be used for general office work. The ceiling will be lay-in ceiling tile and the walls will be painted an off-white. The luminaries will be cleaned regularly and lamps will be group-replaced when the first failures start to occur.

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Basic equations: Footcandles =

Footcandles =

total lumens striking area square feet of area

(Eq. 2-40)

lamps x lumens per lamp x CU x LLF area (Eq. 2-41)

where: CU = LLF =

LLD = LDD = RSD =

coefficient of utilization light loss factor, which is made up of a number of factors. The ones to be included in most calculations are the LLD, LDD, and RSD lamp lumen depreciation luminaire dirt depreciation room surface depreciation

The coefficient of utilization (CU) of a luminaire is calculated by the zonal cavity method and is a measure of how a specific luminaire distributes light into a given room. The CU takes into account luminaire efficiency, candlepower distribution of the luminaire, room size and shape, mounting height, and surface reflectances. The CU for a specific luminaire must be obtained from the manufacturer's catalog. To determine the CU for a specific application, several values must be determined. x x x x

Effective floor cavity reflectance; Effective ceiling cavity reflectance; Wall reflectance; RCR or room cavity ratio.

Most CU tables are based on a floor cavity ratio (pfc) of 20, so that figure will be used for this example (Table 2-4). If the suspension length of the luminaire below the ceiling is zero, which it is for this example, the ceiling cavity ratio is equal to the ceiling reflectance. If the luminaire is suspended, a ceiling cavity ratio must be calculated before the effective ceiling cavity reflectance can be determined. Reflectance values for various surfaces are available in the IES Lighting Handbook. For this example, 70 percent will be used. The wall reflectance of materials can again be obtained from the IES

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Lighting Handbook. For this example, 70 percent will be used. The room cavity ratio (RCR) must be calculated and it is equal to 2.5 times the area of the walls divided by the area of the work place. RCR = (2.5) (room height - work plane height) x perimeter of walls y area (Eq. 2-42) The work plane height is the level at which most tasks will be performed and is assumed to be 30 inches for this example. RCR = (2.5) (11-2.5) (2 (15+25)) = 4.53 (15) (25)

Table 2-3. Coefficient of Utilization Zonal Cavity Method 4-Lamp pfc 20 pcc 80 70 pw 70 50 30 70 RCR 0 76 76 76 74 1 70 68 66 69 2 65 61 57 64 3 60 55 50 59 4 56 49 45 55 5 51 44 39 50 6 48 40 35 46 7 44 36 31 43 8 40 32 27 40 9 37 29 24 36 10 35 26 21 34 Test No. 7834 S/MH = 1.3. For 2-lamp: multiply above C.U.s by 1.16. For 3-lamp: multiply above C.U.s by 1.09.

50

30

50 50

30

74 66 60 54 49 44 39 36 32 29 26

74 64 56 50 44 39 35 31 27 24 21

70 64 58 52 47 42 38 35 31 28 25

70 62 55 49 43 38 34 30 27 24 21

From the table of coefficients of utilization, the resultant coefficient of utilization must be interpolated between 0.55 and 0.50. The resultant CU = 0.523 Before the calculation to determine the number of lamps required can be

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performed, there are still several decisions that must be made. x

Type of lamp to be used; this affects lumens per lamp. Assume 3150.

x

Lamps per luminaire; this affects the coefficient of utilization, which was calculated. For this calculation, assume four, which is the basis of the CU table.

x

LLD must be determined.

x

LDD must be determined.

x

RSD must be determined.

x

Footcandle level desired must be determined.

Values for LLD, LDD, RSD, and a number of other factors that cause light loss in the space can be found in the IES Lighting Handbook but for most calculations dealing with lighting in noncritical areas all of these factors can be combined into a single factor, which is often referred to as the light loss factor (LLF). For this calculation, an LLF of 0.75 has been assumed. Footcandle levels are recommended for a number of applications in the IES Lighting Handbook. The recommended level for general office work falls between 50 and 150 footcandles depending on the level of difficulty of the task. For this calculation, the level required is assumed to be 100 footcandles. Put all of the numbers into a basic equation (Eq. 2-41) and solve it for the number of lamps required: 100 = lamps x 3150 x 0.523 x 0.75 15 x 25 No lamps = 30.4 At four lamps/fixture = 7.6 fixtures Figure 2-3, Zonal Cavity Calculations, provides a form to be used in making lighting calculation. It, or something similar, shall be used to document all calculations.

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Project Name: _____________________________________________________________________________ Date: _______________ Room Name: __________________ A. ROOM DATA

Reviewed By: _________________________

B. CAVITY DATA

Room

1. Length

ft

Room

9. Height

dimen.

2. Width

ft

Cavity

10. Ratio

sq ft

Ceiling

11. Height

Cavity

12. Ratio

3. Floor area 4. Ceiling ht.

ft

Surface

5. Ceiling

%

Reflect.

6. Wall

%

7. Floor

%

C. FIXTURE DATA ft

18. Cat. No. etc. ft 19. Lamps per fixture

13. Eff. Reflectance

%

Floor

14. Height

ft

Cavity

15. Ratio

8. Fixture mounting ht.

20. Lumens per fixture 21. Coeff. Of util (cu) 22. Light loss factor

16. Eff reflectance

D. FOOTCANDLES

17. Mft.

(LLF)

%

E. CALCULATING CAVITY RATIOS

No. of fixtures required to 5 x cavity height x (length + width)

produce a give number of

Cavity ratio =

footcandles

Length x width

23. Desired lighting level

fc

24. No. of tootcandles produced

ROOM: 27.

by a given no. of fixtures Option A

25. Fixtures fc

CEILING:

Option B

26. Fixtures fc

28.

5 x line 9 x (line 1 + line 2) line 1 x line 2

=

5 x __x (__ + __) __ x __

= __

5 x line 11 x (line 1 + line 2)

=

5 x __x (__ + __) __ x __

= __

=

5 x __x (__ + __) __ x __

= __

line 1 x line 2 FLOOR: 29.

5 x line 14 x (line 1 + line 2) line 1 x line 2

F. CALCULATING NUMBER OF FIXTURES Floor are x desired footcandles 30. No. fixtures = lamps per fixture x lumens per lamp x coeff. Of utilization x light loss factor 31. No. of fixtures = 5 x line 14 x (line 1 + line 2) = 5 x __x (__ + __) __ x __ line 1 x line 2

= __

G. CALCULATING FOOTCANDLES Footcandles = no. of fixture x lamps per fixture x lumens per lamp x 32. Coeff. Of utilization x maintenance factor 33. 34.

Option A

floor area Line 25 x line 19 x line 21 x line 22

=

Option B

line 3 Line 26 x line 19 x line 21 x line 22

=

line 3

___ x __x __ x __ __ x __ ___ x __x ___ x ___ __ x __

= __ = __

Figure 2-3. Zonal Cavity Calculations

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The next task is to lay out the luminaries in the room to determine if they will fit in a logical arrangement. Since the luminaries are being installed in a lay-in ceiling, spacing can only be in multiples of 2 feet. For this example, installation of eight luminaries would require two rows of four luminaries each. Spacing across room = 15 y 2 or 8 feet Between rows and (15 - 8) y 2 or 3.5 feet between wall and closest luminaire (all dimensions are to centerline) Spacing length of room = 25 y 4 or 6 feet Between luminaries in the row and (25 - (3 x 6)) y 2 or 3.5 feet from the wall to the end luminaries The footcandle level that results from the number of luminaries to be installed should then be checked: Footcandles = (8 x 4) x 3150 x 0.523 x 35 = 105.4 (15) (25) The maximum spacing of the luminaries shall also be checked against the mounting height above the work plane (S/MH ratio) to determine if it is within the ratio of the luminaire being used. 8 ft spacing y 8.5 ft mounting height = 0.94 This is well within the 1.3 S/MH ratio of the luminaire used in the example. If the luminaries required could not have been fit into the space in a reasonable layout, or the footcandle levels that resulted from the selected layout were not acceptable, or the S/MH ratio calculated was not less than that of the luminaire being used, then the layout would need to be revised using a luminaire with a different number of lamps or different characteristics. The footcandle level calculated tells us the quantity of light that reaches the work surface. Other factors that affect visual comfort and ability to see include direct glare, indirect glare, reflected glare, and veiling reflections. In areas where seeing tasks are critical, these must also be evaluated. See the IES Lighting Handbook and other lighting design and application

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guides for additional information on these subjects. 2.3.10.2 Example No. 2--Point-by-Point Calculation. Conditions: Referring to the luminaire layout for Example No. 1, calculate the footcandle level on a desk located at point No. 1. For this calculation, use the candlepower distribution table (Table 2-4) and assume that no light is reflected from the end wall. Point-to-point calculations are typically used to determine the footcandle level, either horizontal or vertical, on a specific task location from a point source or multiple point sources of light. Illumination on the task is inversely proportional to the square of the distance from the source of illumination. Table 2-4. Candlepower Distribution Curve 4-Lamp Angle

45o

End 0 5 15 25 35 45 55 65 75 85

3429 3396 3293 3061 2649 1982 1229 681 314 94

Cross 3429 3401 3328 3133 2814 2051 1110 425 218 90

3429 3460 3401 3245 2906 2188 1247 662 306 78

Basic equations: Footcandles (horizontal plane) Fc(h) = candlepower x cos ș distance2

(Eq. 2-43)

Footcandles (vertical plane) Fc(v) = candlepower x sin ș distance 2

(Eq. 2-44)

where:

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Candlepower (CP)

=

the candlepower of the source in the direction of the ray

Cos ș

=

height above task (H) y actual distance from task (D)

Sin ș

=

horizontal distance from task (R) y D

Using the above data, calculate the horizontal footcandles on the work surface 4 feet horizontal from the luminaire. (Figure 2-4)

H 8.5 FT 0 ACTUAL DISTANCE OF LIGHT SOURCE FROM TASK POINT

VERTICAL HEIGHT OF LIGHT SOURCE FROM WORK SURFACE

WORK SURFACE

R 4 FT HORIZONTAL DISTANCE OF LIGHT SOURCE FROM TASK POINT

Figure 2-4. Calculation for Task Illumination

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D = (H2 + R2)½ = (8.52 + 42)½ = 9.4 Cos ș = H y D = 8.5 y 9.4 = 0.904 ș = Arc cos 0.094 = 25.3o Use candlepower from Table 2-5 at 25o = 3245 Fc(h) = (3245 x 0.904) y 9.42 = 33.2 fc To determine the total footcandles on the task, the same calculation must be made for each luminaire that could contribute to the illumination level. All of the contributions would then be totaled. Contribution from the luminaire on the opposite side of the point will be the same as calculated above. The next pair of luminaries are close enough that their contribution must also be checked. Calculate footcandles contributed by one luminaire horizontal distance F = (42 + 62)½ = 7.2 ft D = (8.52 + 7.22)½ = 11.14 ft Cos ș = 8.5 y 11.14 = 0.763 ș = arc cos 0.763 = 40.27o Use value for candlepower at 45o with respect to the luminaire and interpolate between 35o and 45o values (Table 2-5). Use 2420 for candlepower. Fc = (2420 x 0.763) y (11.14)2 = 14.88 fc The footcandle level on the task is the sum of the contributions from the four closest luminaries. Fc total = (33.2 x 2) + (14.88 x 2) = 96.16 fc The IES Lighting Handbook contains a table to simplify these calculations. If you know the mounting height above the work plane and the horizontal distance from the task, the table provides the angle to be used to enter the candlepower distribution table and a multiplier to be used with the resultant candlepower to calculate footcandle contribution on the task by

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the luminaire. This method is seldom used within a building except where a single workstation may exist within a larger space where a lower average level of illumination is required and a higher level is required at the workstation. This procedure is often used with outdoor lighting systems to determine the lighting levels on parking lots and roadways. It is the basis used by luminaire manufacturers in their computer programs for laying out area and roadway lighting systems. As previously shown in Figure 2-3, a form can be used in making these calculations. This form shall be used with data provided by the manufacturer of the lighting equipment being specified to determine the lighting levels, in footcandles, for the spaces being illuminated. 2.3.11 Grounding Grounding system calculations shall be made for substation and other areas where step potential will be of concern. The subject is too complex for presentation in this design guide. Grounding system calculations shall be in accordance with applicable sections of ANSI/IEEE Standard 80. 2.4

DRAWINGS

2.4.1 General The purpose of a design is to develop a set of instructions and rules whereby a contractor can bid the project and, if awarded the contract, build what the designer had in mind. The drawings are a part of that instruction set and describe the location and quantity of materials and equipment needed for the project; the text specifications describe the type and quality of materials and equipment and the quality of workmanship. 2.4.2 Organization The drawings are generally divided into the following groups and appear in the order shown below: x x x x x x x x x

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Electrical Legend and Abbreviations; Site Plan(s); One-Line Diagrams(s); Facility Lighting Plan; Facility Power Plan; Facility Grounding Plan (if needed); Equipment Elevations; Control Schematic Diagrams; Connection Diagrams;

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PROJECT DESIGN ELEMENTS x x


Installation Details; Electrical Schedules.

A general description of each group or kind of drawings is given on the following pages. 2.4.3 Legend The legend is a list of the symbols to be used on the design drawings. Generally, they are based on the standard legend symbols contained in NEMA, ICS, and ANSI Standard Y32. Where a design requires the use of a symbol that is not present on the legend, the symbol shall be added to the legend if it is used on more than one sheet of the design. If it is used on only one sheet, it may be described on that sheet. The standard legend symbols shall be used wherever practical to reduce confusion and time spent on inventing unnecessary new symbols. 2.4.4 Abbreviations The abbreviations used on the electrical drawings shall be listed on the electrical legend sheet to minimize possible confusion with similar abbreviations that are used on the sheets prepared by other disciplines. All abbreviations used on the drawings shall be included in the abbreviations list. Unless a word is used often, it should not be abbreviated. 2.4.5 Site Plan(s) The electrical drawings usually include a plan view of the overall project site that typically shows the following data: relative location of buildings and structures, exterior raceways and circuits, locations of manholes and handholes, exterior lighting, and references to the drawings for buildings and structures that need to be shown in more detail. Often, the large size of a site requires a scale so small that additional site plans at a larger scale are required to show the detail required for the design. The single site plan shall always be provided, but when the scale of the overall site plan is less than 1 inch = 40 feet, detailed site plans at a larger scale shall also be provided. The detailed site plans should always be at the same scale used for process equipment layout if possible; that is, 1 inch = 20 feet or larger. The detailed site plans should be used to show all equipment wiring and general lighting and the overall site plan should be used to highlight the locations of switchgear, motor control centers, transformers, and the ductbank system, including all manhole and handhole locations. The overall site plan can also be used as a key to the detailed site plans and detailed plans for buildings and structures.

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2.4.6 One-Line Diagrams One-line or single-line diagrams are a symbolic representation of the major electrical components of the electrical system of the project and their interconnection. All applicable information shall be included on oneline diagrams as follows.

ESD-106

x

Power sources, including voltage and available short circuit currents;

x

Power ratings, voltages, impedances, connections, and grounding methods of all transformers;

x

Protective relay types and sensing connections;

x

Frame rating, trip rating, and special features of over-current and short circuit protection devices;

x

Size and type of motor control devices;

x

Voltage, enclosure, short circuit, and main bus ampacity ratings of switchgear assemblies, switchboards, motor control centers, and distribution panelboards;

x

Instrumentation, including instrument transformers, instrument switches, voltmeter, and ammeter, with appropriate ratios and ranges;

x

Type and location of surge arresters and capacitors;

x

Identification of all loads;

x

Identification of all distribution system equipment;

x

Key interlock systems;

x

Motor sizes;

x

Generator--size, voltage, phase, and power factor;

x

Function lines to show interaction between components in the system such as protective device trip functions and restraints.

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When the electrical distribution system is too large to be shown on a single drawing, the major components and feeders shall be shown on a single drawing. Additional one-line diagrams shall be provided for individual motor control centers as required to show all the loads supplied from them. 2.4.7 Floor Plans Two types of building floor plans are used to depict the electrical requirements for buildings and enclosed structures: the facility lighting plan and the facility power plan. Although the entire electrical design can be shown on a single drawing when facility lighting and power requirements are minimal, separating of floor plans by the kind of work involved is often a preferred method of design that makes the floor plans less crowded and easier to read. The electrical facility power plans show the general location of equipment to be wired and connected under the electrical specifications, and show the necessary conductors and raceways associated with the work. For facilityexpansions, the power plan shall show the interface with existing facility power system. Symbols used on the drawings are usually not to scale but, by definition, tell the contractor how a particular device is to be connected to the electrical system. Conductor and conduit requirements, definitions, and "homerun" designations are shown on electrical drawings. In some cases the conductor and conduit requirements are called out by the symbol used, in other cases the specific requirements are shown on the drawings, and in still other cases a code is used. The code definition can be either a small circuit callout list located on the drawing or a more complete circuit and raceway schedule for the entire project. The circuit codes and circuit names must be developed for each specific project. Lighting, general purpose outlets, special system equipment, connections to HVAC equipment, and miscellaneous power requirements that are directly related to the building or structure are shown on the facility drawings. Luminaire types are identified and located, general purpose outlets are located, special purpose outlets and power connections are located and identified, and all conduit and conductor requirements associated with the above-named equipment is shown. All panelboards and equipment from which the above luminaire, outlets, and power connections receive their power supply shall be shown on the drawings, or the drawings that show them must be referenced.

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2.4.8 Grounding Plan The grounding Plan should be a separate and complete group of drawings. The set of drawings should show the below-grade grounding such as the ground grid including locations of all ground rods. If the grounding plan is for a facility expansion where electrical service will be provided by the existing facility, show the interconnection of the facility expansion ground grid with the existing facility ground grid. The abovegrade grounding should be shown in plan form, indicating which steel columns, fence or specific equipment require bonding. The type of grounding connection welded type for below-grade and above-grade or bolted type of above-grade shall be shown using appropriate symbols as defined in the legend sheet. 2.4.9 Equipment Elevations Two-dimensional drawings of control pads, switchboards and motor control centers, secondary unit substations and switchgear shall show the arrangement of components of the assemblies. The elevation drawings are usually nonscale drawings. However, their intent is to determine general space requirements for the assembly so they need to be laid out using the dimensions of the equipment being specified. The front elevations typically show main service and feeder circuit protective devices, metering, branch circuit protective devices and controllers, terminal board compartments, and future designated space requirements. Control Schematic Diagrams 2.4. 10 The purpose of the electrical control schematic diagram is to illustrate schematically for the equipment supplier and contractor how a system is controlled. The control schematic diagrams contained in the electrical drawing set are for I&C panels, motor starters, contactors, etc., that are to be installed as part of the I&C and electrical systems. Each control schematic diagram shall show all devices that are to be located on the panel starter or contactor and all field-installed devices. Control logic that is provided in a remotely located control panel supplied with equipment shall be shown as a terminal connection. All interfaces with remote equipment shall be clearly shown using appropriate symbols and clearly identified so that the contractor can easily make the interconnections in the field. 2.4.11 Control Panel Drawings. Control panel drawings provide the following information to the contractor: x Panel size; x Major panel components and their layout;

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x Panel installation. The following format and content guidelines shall be followed in preparing control panel drawings:

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x

Show full views of the front of the panel. (Partial views may be used for details.)

x

Show front and side views as a minimum. Show further views as needed.

x

Show smaller panels (wall mount) as manufactured item (e.g., Hoffman or equal).

x

Show only outlines of instruments and devices. Show future instruments and controls in phantom.

x

Show overall panel dimensions (H,W,D). Dimension the location of only critical components. Use drawing scale for location of other components.

x

Show conduit and tube entry points.

x

Show the mounting of the panel (installation detail). Preferred mounting of freestanding panel is 3-1/2-inch-thick concrete pad secured with anchor bolts and holddown clips.

x

Show location key plans for each panel and include the sheet number of the mechanical plan where the panel is located, building and room names where the panel is located, title (e.g., LP-XXX LOCATION PLAN), scale (1s=100c or 1s=50c), panel name (e.g., LP-XX), and north arrow.

x

Note any special features on the drawing (e.g., special enclosure).

x

Include schedules for panel face mounted devices and annunciators. Include device number (as noted on panel drawing), tag number, and nameplate or service legend inscription in the schedules. Annunciator schedules shall include point location (row-column), alarm tag number, and annunciator window inscription.

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Refer to Figure 2-5 for an example of a panel drawing. Installation Details 2.4. 12 Installation details illustrate specific requirements that an engineer/designer has in mind for construction, installation, or connection of equipment and/or materials that are better shown by a drawing than by wordy specifications. Many installation details are provided in the standard drawing package and should be used whenever possible. If the engineer/designer encounters a unique situation that requires a special detail, he or she shall prepare a new detail using materials that are equivalent to those used in the standard detail and then have the detail reviewed for constructability and compatibility of materials. Thedetails to be used shall always be referenced on the plan drawings by either notes or symbols. Details should, where possible, include notes to indicate the area and/or circumstances where they apply.

2.4. 13 Electrical Schedules. The electrical drawing package usually includes some electrical material or equipment listings in schedule format. Typical schedules provided are: x x x x x

Lighting fixture schedule; Distribution panel schedules; Conduit and cable schedules; Special electrical device schedules; Pull box and junction box schedule.

On small projects, separate drawings for the schedules may not be required. They shall be located throughout the drawing set where they are required. On very large projects, it is better to include all of the schedules as a supplement to the specifications so they can be found and handled more easily. The use and presentation of schedules shall be reviewed for each project. There is no single correct way to prepare and present them. 2.5 PROJECT FILES Each engineer/designer shall keep a project file that contains all information received and/or originated by the individual during the performance of his or her duties on the project. The project file shall contain a copy of the project instructions and all addenda to it, telephone conversation record of all phone conversations, copies of all written correspondence and memorandums, field notes, and copies of all design calculation prepared as required by paragraph 2.3, Design Calculations. The project files shall be kept in a notebook with identified divider tabs.

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At the completion of the project, each individual shall purge the file of the project instructions and other memos that were originated by other team members and submit the purged project files to the project manager for inclusion in the overall project file. Any memos, instruction sets, and similar items prepared by the individual shall be left in his or her project file so that originals of all material prepared or used on the project are contained within the overall project files.

8”

24”

1

FULL LENGTH PIANO TYPE HINGE

2 3

6

9

4

7

10

30”

5

8 15

18

13

16

19

14

23

11

12

20

17 21

24

22

24 24

27 25 29

30 31 32 33

FRONT

SIDE

SCALE 1 ½“ = 1’-0”

SCALE 1 ½“ = 1’-0”

Figure 2-5. Example Panel Drawing

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Chapter 3

STANDARD ELECTRICAL DESIGN PROCEDURES


ŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮŮ

Note: All references to the National Electrical Code (NEC) are based on the 2005 Edition of the NEC. 3.1 GENERAL APPROACH Because no single electrical system is adaptable to all projects, the specific requirements of each project must be analyzed and the electrical system designed to meet those needs. Any approach to providing the required design shall include several considerations that will affect the overall design. First, safety of personnel and preservation of property are important factors in the design of electrical systems. Second, reliability and continuity of service is of utmost importance. This chapter discusses many of the basic decisions that shall be made during a design, identifies reference sources that shall be used to help make those decisions, and outlines the materials that shall be used in implementing those decisions. 3.1.1 Types of Electrical Systems Electric power is distributed through a network of conductors and electric circuit protective and control equipment from its source of supply in the serving utility to the utilization equipment located on the premises. This assembly of conductors and equipment is called the electrical distribution system and is the main subject of this design guide; other subjects covered include motor controls, lighting, and special systems such as telephone, paging, and fire alarm. 3.1.2 References There have been a number of codes, standards, and handbooks prepared on the basic subjects covered by this design guide. A brief list of some of the more applicable references, many of which have been used in the preparation of this design guide are contained in Appendix A. The latest edition of each of these references shall be used.

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3.1.3 Plant Distribution Systems A variety of basic circuit arrangements is available for industrial plant power distribution. Selection of the best system or combination of systems will depend upon the needs of the plant process. In general, system costs increase with system reliability if component quality is equal. The first step is the analysis of the plant process to determine its reliability need and potential losses and costs in the event of power interruption. Some plant processes are minimally affected by interruption. Other plant processes may sustain long-term damage or experience excessive cost by even a brief interruption, therefore, a more complex system with an alternate power source for critical loads may be justified.

3.1.3.1 Simple Radial System Figure 3-1 shows a simple radial system where the distribution is at the utilization voltage. It is the simplest and lowest cost way of distribution power. A single primary service and distribution transformer supply all the feeders. This system is satisfactory for small industrial installations where process allows sufficient down time for adequate maintenance and the plant can be supplied by a single transformer. 3.1.3.2 Expanded Radial System Figure 3-2 shows an expanded radial system. The advantage of a simple radial system may be applied to larger loads by using an expended radial primary distribution system to supply a number of unit substations located near the load, which in turn supply the load through radial secondary systems. This system provides better voltage conditions, lower system losses, less expensive installation cost than using relatively long, highamperage, low-voltage feeder circuits. 3.1.3.3 Primary Selective System If pairs of substations are connected through a secondary tie circuit breaker, the result is a secondary selective system (see Figure 3.3). Each unit substation is connected to two separate primary feeders through switching equipment to provide a normal and an alternate source. Upon failure of the normal source, the distribution transformer is switched to the alternate source. Switching can be either manual or automatic, but there will be an interruption until load is transferred to the alternate source. Cost is somewhat higher because of duplication of primary cable and switchgear.

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3.1.3.4

Secondary Selective System (Double-Ended Substation with Single Tie) If pairs of substation are connected through a secondary tie circuit breaker, the result is a secondary selective system (See Figure 3.4). Under normal conditions, the system operates as two separate radial systems with the secondary bus-tie circuit breaker normally open. A key interlock system is used to prevent parallel operation of the transformers. Maintenance of primary feeders, transformer, and main secondary disconnection means is possible with only momentary power interruption. If the primary feeder or transformer fails, supply is maintained through the secondary tie circuit breaker. To allow for this condition, the following should be considered: x x x x

Oversizing both transformers so that one transformer can carry the total load Providing forced-air cooling to the transformer in service for the emergency period Shedding nonessential load for the emergency period Using the temporary overload capacity in the transformer and accepting the loss of transformer life.

The double-ended substation with single tie configuration is the preferred method of power distribution in the Metropolitan’s water treatment plants. Primary power is distributed at 4160 volts to the substation and secondary power is distributed at 480 volts from the substation to motor control centers and switchboards. 3.1.3.5

Secondary Selective System (Individual Substations with Interconnecting Ties) Figure 3-5 shows modified secondary selective system with only one transformer in each secondary substation. Adjacent substations are interconnected in pairs by normally low-voltage tie circuit. When the primary feeder or transformer supplying one secondary substation bus is out of service, essential loads on that substation bus can be supplied over the tie circuit. Operation of the system is somewhat complicated if the two substations are separated by distance. A key interlock system would be required to avoid typing two substations together while they are both energized.

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BUS DUCT

PANEL

FIGURE 3-1 SIMPLE RADIAL SYSTEM

FIGURE 3-2 EXPANDED RADIAL SYSTEM ESD-106

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FIGURE 3-3 PRIMARY SELECTIVE SYSTEM

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SECONDARY UNIT SUBSTATION

FIGURE 3-4 SECONDARY SELECTIVE SYSTEM (DOUBLE-ENDED SUBSTATION WITH SINGLE TIE)

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FIGURE 3-5 SECONDARY SELECTIVE SYSTEM (INDIVIDUAL SUBSTATIONS WITH INTERCONNECTING TIES)

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual 3.1.4 Voltage Considerations ANSI/IEEE Std 141 refers to ANSI C84.1 for nominal standard system voltages and their associated tolerances. The standard defines three voltage classes: x x

x

Low voltages are used to supply utilization equipment and are 1,000 volts and less. Medium voltages are used as primary distribution voltages to supply stepdown transformers to low-voltage systems and are greater than 1,000 volts but less than 100,000 volts. Medium voltages of 13,800 volts and less are also used to supply utilization equipment such as large motors. High voltages are used to transmit large amounts of electrical power between transmission substations, and are higher than 100,000 volts.

The nominal voltage of the systems covered by this design guide will be in either the low or medium voltage class. Table 3-1, Standard Nominal System Voltages and Voltage Ranges in Chapter 3 of ANSI/IEEE Std 1411993 lists the standard and nonstandard nominal system voltages within all three of the voltage classes. The table uses a system voltage nomenclature that describes how the nominal voltage is supplied. A single-number, single-phase voltage, such as 120 volts, indicates a twowire single-phase system where the voltage indicated is the nominal voltage between the two wires. A single-number, three-phase voltage, such as 480 volts, indicates a three-wire, three-phase system where the voltage designates the nominal voltage between any two phase wires. A two-voltage designation where the smaller number is first, such as 120/240, indicates a single-phase three-wire voltage in which the nominal voltage between phase conductors is 240 volts and the nominal voltage between either phase conductor and neutral is 120 volts. If the two numbers are reversed with a Y between, such as 480Y/277 volts, a three-phase four-wire system supplied by a wye connected transformer is indicated. The first number indicates the nominal phase-to-phase voltage and the second number indicates the nominal phase-to-neutral voltage.

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3.1.5 Voltage Selection The preferred utilization voltage for industrial plants is 480Y/277 volts, three-phase, four-wire. Three-phase loads can then be supplied at 480 volts with single-phase loads such as high bay lights supplied at 277 volts. Small dry-type transformers rated 480-120/240 or 208Y/120 are then provided to supply 120-volt lighting and convenience receptacles. The three-phase 208Y/120 volt utilization voltage is preferred except where only very small loads are involved because it also allows small three-phase loads to be supplied and it balances the loads on the 480Y/277 volt system. Where double-ended unit substations with tie breakers are used, loads shall not be connected phase-to-neutral on the 480-volt system to simplify the ground fault protection scheme. Where individual loads of 500 kVA or more must be supplied, 4,160 volts should be considered for the utilization voltage for this equipment. Power distribution voltage within a plant site is often dependent on the supply voltage available from the serving utility. In a case where the load on the plant site is small and located in a concentrated area, service from the utility at 480Y/277 volts shall be specified. Larger sites where the loads are spread out and a number of unit substations will be required shall be supplied at a higher voltage. If there are large motors that could be supplied at a higher voltage, the distribution voltage shall be selected to supply the large motors without additional transformation. This would make 4,160 volts three-phase the preferred distribution voltage unless very large motors are involved. 3.1.6 Voltage Rating Most electrical utilization equipment has a nameplate voltage that matches the nominal supply voltage for which the equipment is designed. Motors are the exception. Motors designed for connection to a 480-volt threephase system are rated 460 volts three-phase. Similar differences are found in the ratings for motors designed for operation on 120-volt, 208-volt, 240-volt, and 4,160-volt systems. See Table 3-7 in Chapter 3 of ANSI/IEEE Std 141-1993 for the nameplate voltages of motors as specified in NEMA MG1. Table 3-8 in Chapter 3 of ANSI/IEEE Std 1411993 also contains information on the effect of voltage variations on the operation of motors and other equipment. 3.1.7 Protection/Coordination Philosophy The primary objectives of electrical system protection and coordination are to prevent injury to personnel, to minimize damage to the system components, and to limit the duration of outages that result from the operation of the system protective devices. Protection of personnel and equipment shall be given first consideration and then coordination of devices within the system to limit the extent of service interruptions.

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3.1.7.1 Protection Equipment. The electrical system components shall be protected against overcurrent, phase to phase faults, and phase to ground faults. There are two basic types of equipment available to perform these protection functions: the fuse and the circuit breaker. There are a variety of devices that fall within these two broad categories, and in this design guide we will only review a few of them. A.

Fuses. A fuse may be defined as a device that protects a circuit by fusing open its current-responsive element when an overcurrent or short circuit passes through it. It combines both the direct sensing and interrupting elements in one self-contained device. A fuse is also direct-acting in that it responds to a combination of magnitude and duration of circuit current flowing through it, it is single phase, it is nonresettable, and it is not capable of being used to interrupt a circuit during normal operation. It must be used in conjunction with a switch for normal circuit interruption.

B.

Low Voltage Circuit Breakers. The NEC defines a circuit breaker as a "device designed to open and close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent without injury to itself when properly applied within its rating." Low voltage circuit breakers have contacts to interrupt the circuit that are isolated from the thermal or solid state elements, which determine that an overcurrent condition has occurred. Low voltage circuit breakers are divided into two basic classes and three types. 1.

2.

Classifications: a. Low-voltage power circuit breakers b. Molded-case circuit breakers Types: a. Low-voltage power circuit breakers (LVPCBs) b. Molded-case circuit breakers (MCCBs) c. Insulated-case circuit breakers (ICCBs)

Low-voltage power circuit breakers are open-construction assemblies on metal frames with all parts designed for accessible maintenance, repair and ease of replacement. They are intended for service in switchgear compartments or other enclosures of dead-front construction. Tripping units are electromagnetic overcurrent direct-acting type or solid-state type. Solid-state trip units are preferred because of the wide range of adjustments through use of interchangeable trip rating plugs, tripping selectively and accurately.

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Molded-case circuit breakers are switching devices and automatic protective devices assembled in an integral housing of insulating material. These breakers are generally capable of clearing a fault more rapidly than power circuit breakers and are available in the following general types: x x x

x

Thermal magnetic—employs thermal tripping for overloads and instantaneous magnetic tripping for short circuits Magnetic—employs only instantaneous magnetic tripping where only short-circuit interruption is required Integrally fused—combines regular thermal magnetic protection against overloads and lower value short-circuit faults with current-limiting fuses responding to higher shortcircuit currents. Current-limiting—provides high interruption rating protection, plus it limits let-through current and emergency to a value significantly lower than the corresponding value for a conventional molded-case circuit breaker.

Molded-case circuit breakers are generally not designed to be maintained in the field as such are sealed to prevent tampering. Insulated-case circuit breakers utilize characteristics of design from both power and molded-case types. The frame size of this type of breakers I larger than the same size for molded-case breakers. The trip unit can be interchanged, and the breaker can be designed to fix-mounting as well as with drawout configuration. The interruption duty of this type of breaker can be faster than that of molded-case breakers but not fast enough to be a current limiting type. Insulated-case circuit breakers are partially field-maintainable. C.

3.1.7.2

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Medium Voltage Circuit Breakers. Circuit breakers for 5- and 15-kV systems are available in either of two types of construction. The air magnetic contactor type has been the standard of the industry for a number of years. Recent changes in technology have resulted in the manufacture of vacuum and SF6 interrupter circuit breakers. Vacuum interrupter circuit breakers are currently the standard for 5- and 15-kV class circuit breakers. They are integrated with protective relays as may be required for the application, and are installed in switchgear assemblies. They are available in 1,200-, 2,000-, and 3,000-ampere ratings at both 5- and 15-kV. Application.

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual Circuit breakers shall be used to provide overcurrent and short circuit protection on the 4.16-kV distribution systems in water treatment plants and as primary protection for medium voltage transformers. Circuit breakers shall also be used on the load side of all transformers. Fuses shall be used in combination with circuit breakers where current limiting protection is required. A.

Low Voltage Systems. Protection for low voltage systems shall be provided by the use of a combination of low voltage circuit breakers. x Motor branch circuit breakers installed as part of a combination motor starter shall be magnetic-only type. x Motor branch circuit breakers installed as part of a reduced voltage starter or to feed an adjustable frequency drive unit shall be thermal magnetic type. Provide adjustable magnetic trip units for all sizes for which they are available. x Branch and feeder circuit breakers 225 amps and smaller shall be thermal magnetic type. Adjustable magnetic trips shall be specified for all frame sizes where they are available. x Larger branch circuit breakers shall also be the thermal magnetic type with adjustable magnetic trip units. x Feeder circuit breakers from 225 amps through 800 amps shall be molded case with solid state trip units. x Feeder circuit breakers larger than 800 amps shall be molded case with solid state trip units and 100 percent load rating. x Transformer secondary and service entrance circuit breakers 600 amps and less with no subfeed breakers rated 225 amps or more shall be molded case thermal magnetic type with adjustable magnetic trip units. x Transformer secondary and service entrance circuit breakers rated 400 or 600 amps with subfeed breakers rated 225 amps or more and all similar breakers larger than 600 amps shall be low voltage power circuit breakers with solid state trip units. Breakers 1,000 amps and larger shall also be 100 percent load rated.

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual x Secondary unit substation main and feeder circuit breakers 800 amp frame and larger shall be insulated case circuit breakers with solid state trip devices. x Low voltage motor control center main circuit breakers shall be insulated case circuit breakers with solid state trip devices. B.

Low Voltage Ground Fault Protection. Ground fault protection shall be provided on all transformer secondary and service entrance breakers rated 600 amperes or more, all feeder breakers rated 400 amps or more that are downstream of a circuit breaker equipped with ground fault protection. Ground fault protection on transformer secondary and service entrance circuit breakers and feeder breakers shall have adjustable time delays and shall be zone selective interlocked to minimize outage to the zone nearest the ground fault.

C.

Medium Voltage Systems. Protection for medium voltage systems shall be specified to be metal clad switchgear with vacuum interrupter type circuit breakers. All medium voltage main and feeder circuit breakers shall be equipped with time and instantaneous phase overcurrent and time and instantaneous ground overcurrent as a minimum. Motor branch circuits shall have thermal overload relays with instantaneous overcurrent trip attachments, undervoltage and phase sequence relay, and overcurrent ground relay with instantaneous trip attachments as a minimum. This protection for motor branch circuits may be provided by a solid state motor protection module that also incorporates optional modules to monitor motor and bearing temperature.

3.1.7.3 Coordination. Coordination is the selecting or setting, or both, of protective devices to minimize the portion of a power distribution system that is affected by a fault within the system. Although maximum effort needs to be made to select and set protection equipment to provide coordination, protection of personnel, and minimization of equipment damage must be considered first. Safety of life is always the most important consideration. The system shall preserve the safety of the general public and be capable of safe operation by plant personnel. The second consideration should be the preservation of property. Next, the need for reliability must be balanced against the cost of providing the electrical system that provides the level of reliability desired. If the impact of a short outage has little affect on the cost of plant operation, additional expense to provide a fully coordinated system is

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual probably not justified. Should a short outage adversely affect the cost of plant operation, then the additional expense of a fully coordinated system may be justified. The cost/benefit ratio of each situation shall be reviewed and an economic balance struck. 3.1.8 Equipment Heat Dissipation Data Heat is generated in electrical equipment due to the electrical losses that occur within the equipment. An estimate of the electrical losses shall be developed and added to the cooling requirements of the space where the electrical equipment is installed. Table 10-1, Range of Losses in Power System Equipment, in Chapter 10 of ANSI/IEEE Std 141-1993 contains a list of energy losses for a number of types of electrical equipment. Table 3-1 shows energy losses for the equipment that will be most often found in water treatment facilities. 3.2 LOCATING ELECTRICAL EQUIPMENT Electrical equipment is designed for a variety of environmental conditions, and it is important that the equipment selected be suitable for the location where it is to be installed. Both the basic design of the equipment and the requirements of the NEC shall be taken into account when locating electrical equipment. 3.2.1 Equipment Rooms and Buildings Article 110 of the NEC contains a number of specific requirements that pertain to the location of electrical equipment. NEC Table 110.26(A)(1) defines the working space required in front of equipment rated 600 volts and less. NEC Table 110.34(A) defines the working space required in front of equipment rated above 600 volts. Note that these are minimums and do not provide comfortable working space. Table 3-1 Losses in Electrical equipment Percent Energy Loss (full load)

Component Medium voltage switchgear

0.005-0.02

Transformers

0.4-1.90

Medium voltage starters

0.02-0.15

Low voltage switchgear

0.13-0.34

Low voltage motor control

0.01-0.40

Cable

1.00-4.00

Motors x 1-10 hp

14.0-35.0

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x 10-200 hp

6.00-12.00

x 200-1,500 hp

4.00-7.00

Static variable speed drives 6.00-15.00 Note: Use high end of range except when more accurate data are known or provided.

NEC Article 408 contains additional requirements that pertain to the location of switchboards and panelboards. NEC Article 450 contains a number of specific requirements that are applicable to the installation of different types of transformers. It also contains specific requirements for construction of transformer vaults. Major electrical equipment such as transformers, switchgear assemblies, switchboards, and motor control centers shall be installed in dedicated rooms or buildings. Smaller equipment such as individual motor starters and panelboards shall be installed in mechanical spaces that are ventilated and dry. All equipment rated above 600 volts, except padmounted transformers and metal enclosed outdoor switchgear assemblies, shall be located in dedicated spaces that are only accessible to qualified persons. Rooms containing motor control centers should be ventilated, not air conditioned, so that the ambient temperatures around both the motors and their controllers are similar. 3.2.2 Equipment Enclosures Electrical equipment enclosures shall be designed for the conditions that they will be subject to when installed. ANSI/NEMA 250 defines the types of enclosures and the conditions for which those enclosures were designed. The most often used NEMA enclosure types are as follows: x x x x x

NEMA Type 1; NEMA Type 3R; NEMA Types 4 and 4X; NEMA Type 7, Class I, Group A, B, C, or D; NEMA Type 12.

See Chapter 16 of the Switchgear and Control Handbook for a complete list of the NEMA enclosure types and their intended uses. Appendix D also describes each NEMA enclosure type.

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3.2.2.1 Indoor Locations. Enclosures installed indoors in dry industrial type areas shall be NEMA 12. NEMA 1 enclosures may be used in electrical rooms, offices, and laboratory areas where flying dust and debris would not be present. NEMA 4 enclosures shall be installed in indoor damp and wet areas that do not have corrosive atmospheres. Where corrosive atmospheres are also anticipated, 316 stainless steel or reinforced fiberglass NEMA 4X enclosures shall be installed. 3.2.2.2 Outdoor Locations. Enclosures installed outdoors must be designed to meet a number of conditions. If the atmospheric conditions are not known, 316 stainless steel or reinforced fiberglass NEMA 4X enclosures shall be installed. If it is known that no corrosive atmospheric conditions can be expected, then NEMA 3R or NEMA 4 enclosures could be used. NEMA 4 enclosures shall be used in process areas where washdown of the area can be expected, and NEMA 3R can be used for disconnect switches and similar equipment where it is located away from process equipment. 3.2.2.3 Hazardous Locations. Equipment enclosures in hazardous locations shall be classified for use in the hazardous classification that applies. NEMA 7 enclosures for use in Class I Group A, B, C, and D locations (gaseous hazards) and NEMA 9 for Class II Groups E, F, and G locations (explosive amounts of dust) are the two most often needed. 3.3 SWITCHGEAR Switchgear is a general term covering switching and interrupting devices alone or in combination with other associated control, metering, protective, and regulating equipment. A power switchgear assembly consists of a complete assembly of one or more of the above-noted devices and main bus conductors, interconnecting wiring, accessories, supporting structures, and enclosures. Both medium voltage and low voltage enclosed switchgear will be reviewed in this design guide. See Chapter 10 of ANSI/IEEE Std 141-1993 and ANSI/IEEE C37.20-1, C37.20-2, C37.20-3, and C37.100 for additional information on switchgear. 3.3.1 Low Voltage Two types of low voltage enclosed switchgear are used in power distribution systems: the metal-enclosed low voltage power circuit switchgear, and the power switchboard.

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3.3.1.1 Metal-Enclosed Switchgear. Metal-enclosed low voltage power circuit switchgear is constructed in accordance with ANSI C37.20-1 and meets the requirements of UL Standard 1558. It features individually mounted air break power circuit breakers in drawout construction. Power circuit breakers both with and without current limiting fuses are available. Circuit breakers are equipped with solid-state tripping systems and offer a wide range of adjustability. See additional requirements defined in Metropolitan's Standard Specifications Sections Catalog. Metal-enclosed low voltage power circuit switchgear shall be used where the available fault current exceeds 50,000 amps symmetrical at 480 volts or 65,000 amps symmetrical at 208 or 240 volts. 3.3.1.2 Power Switchboards. Power switchboards are available in either group-mounted or individually mounted configurations. The groupmounted configuration is normally used for small boards and in commercial construction. Both types are constructed in accordance with applicable provisions of UL 891 and NEMA PB-2. The main circuit protective devices in group-mounted switchboards are either fixed or drawout-mounted, but the branch devices are all fixedmounted. The main device is either a molded case circuit breaker, a molded case circuit breaker with solid state trip units, an air break power circuit breaker, or a bolted pressure switch. The branch devices are either molded case circuit breakers with or without solid state trip units, or fused switches. The standard short circuit rating for group mounted switchboards is 50,000 amps RMS symmetrical, but higher ratings are available. See Metropolitan's Standard Specifications Sections Catalog for more detailed requirements of this equipment. Both the main and feeder circuit protective devices shall be drawout type in individually mounted configurations. Circuit protective devices shall be applied in a manner consistent with applicable portions of Section 3.1.6, Protection and Coordination Philosophy. The standard short circuit rating for switchboards with individually mounted drawout circuit breakers is 50,000 amps RMS symmetrical, but higher ratings are available. See Metropolitan's Standard Specifications Sections Catalog for more complete and detailed requirements for this equipment. Switchboards with group-mounted circuit protective devices shall be used where the main bus rating is 800 amps or less, the fault current available is less than 50,000 amps RMS symmetrical, and the feeder and/or branch circuit protective devices are all 225 amps or less. Where the main bus rating must be greater than 800 amps and feeder breakers of 400 amps or larger are required, switchboards with individually mounted circuit

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual protective devices shall be used if the fault current available is 50,000 amps RMS symmetrical or less. Where higher fault currents are available, metal-enclosed low voltage power circuit switchgear shall be used. 3.3.2 Medium Voltage (4.16 kV through 13.8 kV) Two types of medium voltage switchgear are available: metal-clad switchgear and load interrupter switchgear. Both are available for either indoor or outdoor installation. Metropolitan standard is metal-clad switchgear with vacuum circuit breakers. 3.3.2.1 Metal-Clad Switchgear. Metal-clad switchgear shall be an assembly of drawout vacuum circuit breakers, auxiliary equipment, metering equipment, and insulated copper bus bars enclosed in a rigid metal assembly and constructed in accordance with ANSI C37.20.2. Each compartment in the assembly shall be isolated from all other compartments by grounded metal barriers. The circuit breakers shall be horizontal drawout type on rails. The breakers shall be operated by a motor-charged, spring-stored energy mechanism. The mechanism shall be front accessible and will be charged normally by a universal electric motor and in an emergency by a manual handle. Each circuit breaker shall contain three vacuum interrupters separately mounted. The detailed requirements for metal-clad switchgear shall be as specified in Metropolitan's Standard Specifications Sections Catalog. Metal-clad switchgear shall be provided as the service entrance equipment for all medium voltage distribution systems that require more than one main device and more than two feeder devices downstream of each main device. Metal-clad switchgear shall also be provided where large motors are served directly from the medium voltage distribution system. 3.4 TRANSFORMERS Unit substations and pad-mounted transformers are both available to transform medium voltage primary power to lower utilization voltages. The lower voltage may be either a low voltage class such as 480 volts or a medium voltage class such as 4,160 volts. There are several basic differences between these transformer types that must be kept in mind when selecting one for an application.

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3.4.1 Pad-Mounted Pad-mounted transformers are intended for use with underground power distribution systems. They offer flexibility and provide a pleasing installation. Their tamperproof construction allows installation in locations accessible to the general public without the need for protective fencing or vaults. They are oil-filled and are not suitable for indoor installation. Compartmental type pad-mounted transformers are designed for the underground entrance of primary and secondary conductors. Provisions are available for live or dead front primary termination on radial or loop feed systems. Secondary connections are spade terminals mounted to the tank wall. Three-phase pad-mounted transformers are available from 45 kVA to 5,000 kVA. They are constructed for a 65o C rise over a 30o C ambient and have no provisions for increasing overload capability. 3.4.2 Unit Substations A unit substation consists of a substation type transformer designed for close coupling to a primary switch or switchgear assembly, and a secondary switchgear assembly. Each of the three parts need to be looked at individually because there are several options available for each. The substation transformer may be installed along or with either the primary or secondary switchgear assembly where proper bushings and terminal cabinets are provided and where the switching and protection functions are provided by remotely located equipment. 3.4.2.1 Primary Switch. Several options are offered for the primary switch of a unit substation. A metal-clad nonfused interrupter switch shall be provided where transformer protection is provided elsewhere. Should transformer protection be required, a metal-clad vacuum circuit breaker shall be bolted to the high voltage flange of the transformer. Should a loop feed or primary selective switching be required, a metal-clad switchgear assembly shall be bolted to the high voltage throat of the transformer to provide both transformer protection and flexibility in the distribution system.

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3.4.2.2 Transformer Section. The transformer section shall be either liquid-filled, dry type, or cast coil type. Selection of the transformer must be made based on where the transformer is to be installed and the expected overload requirements. A.

Liquid-Filled Transformers. Transformers are available from 225 to 5,000 kVA with a variety of high and low voltage windings. Several types of insulating liquid or fluid are available and NEC Article 450 Section II contains special provisions that cover the use of different liquids or fluids in different locations. The standard load rating for liquid-filled transformers is at a 65o C rise. Liquid-filled transformers are available with a 55/65o C rating, which increases the nominal rating of the transformer at a 65o C rise by 12-1/2 percent. In addition, the overload capability of liquid-filled transformers can be increased by the addition of fans. The self-cooled rating of transformers from 225 to 2,000 kVA can be increased by 15 percent and the self-cooled rating of transformers from 2,500 to 5,000 kVA can be increased by 25 percent.

B.

Dry-Type Transformers. Dry-type transformers are available in either ventilated or nonventilated construction for both indoor and outdoor applications. The standard load rating for a drytype transformer is at a 115o C rise over a 40o C ambient. These transformers are capable of carrying a 15 percent overload continuously without exceeding the 150o C enclosure temperature. They are also available with an 80o C rise over a 40o C ambient capable of carrying a 30 percent overload continuously without exceeding 150o C in the transformer enclosure. Dry type transformers are available in sizes from 225 to 2500 kVA self-cooled ratings, and the self-cooled rating can be increased 33-1/3 percent for short-term load peaks with the addition of fans. The standard basic impulse level (BIL) for dry type transformers is typically less than the standard for (BIL) liquid-filled transformers and needs to be kept in mind when selecting transformers.

3.4.2.3 Secondary Switchgear Assembly. Several options are available for the equipment to be located on the secondary of a unit substation. They range from an air terminal cabinet for termination of either a bus duct or cables to a metal-enclosed low-voltage power circuit switchgear. The circuit protective devices used shall be dependent upon the needs of the system.

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3.4.3 Equipment Selection Unit substations are Metropolitan standard. Pad-mounted transformers shall only be used where transformer requirements are so small that unit substations are not available. 3.5 MOTOR CONTROL EQUIPMENT Motor control equipment is a general term that covers a range of voltage and horsepower ratings and innumerable combinations of equipment arrangements and operational functions. All such equipment is designed and produced in accordance with NEMA Standards Publication Industrial and Control Systems. In addition to ac motor starters, this section includes discussions of adjustable speed controllers, DC motor controls, and power factor improvement. Section 10.6 of ANSI/IEEE Std 141-1993 identifies a number of factors that must be kept in mind when selecting the controller for a motor. 3.5.1 Low Voltage In ac motor control, contactors are normally used for controlling the power supply to the motor. The contactor, when applied in conjunction with a thermal overload heater block, is called a starter. The starter is then applied in combination with either a magnetic-only circuit breaker or a thermal magnetic circuit breaker, and is called a combination motor starter. The thermal overload heater block provides overload protection, and the circuit breaker provides short circuit protection. The standards for magnetic controllers rated 115 through 575 volts are summarized in ANSI/NEMA ICS2. Motor starters for Metropolitan projects shall be sized as shown in Table 2-1 for 480-volt three-phase motors. Starters for motors operating at other voltages shall be sized in accordance with appropriate NEMA standards. There are several types of low-voltage motor starters available. Following is a list of the more commonly used types and a brief description of each. A more complete description can be found in either ANSI/IEEE Std 1411993 or the Switchgear and Control Handbook. x Manual motor starter. A manual starter is a manually operated switch that is rated for control of induction loads and includes thermal overload protection. The manual starter may not provide undervoltage protection. x Magnetic, nonreversing motor starter. Provides fullvoltage starting for motors that must be started frequently and are suitable for use with remote control devices such as pushbuttons, selector switches, or similar pilot devices. The magnetic, nonreversing motor starter provides overload

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual protection and can also provide undervoltage protection if momentary contact controls are provided. x Magnetic, reversing motor starter. Control is provided by two contactors wired so that reversing the phases provides the reversing function. In all other respects, control is the same as for magnetic, nonreversing motor starters. Mechanical and electrical interlocks are provided to prevent momentary short circuiting when changing directions. x Combination motor starter. Either a nonreversing or reversing magnetic starter can be provided in combination with a nonfused disconnect switch, a fused switch, or a circuit breaker. The resulting assemblies are then called nonfused nonreversing (or reversing) combination motor starter; fused nonreversing (or reversing) combination motor starter; or circuit breaker type nonreversing (or reversing) motor starter. The control functions are as described above, with the addition of a disconnect function and short circuit protection in the case of the fused and circuit breaker type starters. x Reduced voltage starters. Reduced voltage motor starters include the basic components of a combination motor starter with a means to reduce the inrush current to the motor to some level below that which would be expected should full voltage be applied. Reduced voltage starters shall be provided for all motors 50 hp and larger when installed as part of a retrofit, unless motor starting voltage drop calculations are made that show that the voltage dip that would result from full voltage starting is less than 20 percent. Reduced voltage starters shall be provided for all motors 100 hp or larger when installed as part of new construction, unless motor starting voltage drop calculations are made that show that the voltage dip that would result from full voltage starting is less than 20 percent. Following are the four types of reduced voltage starters that are available from most manufacturers: -

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Autotransformer type (both open transition and closed transition). An autotransformer is used to reduce the voltage being applied to the motor windings.

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual The starting torque will vary almost directly with the variation in motor current. To minimize the short duration, high inrush current that occurs during an open transition, the closed transition connection momentarily uses the autotransformer as a series reactor to minimize the current surge. The autotransformer type reduced voltage starter offers the highest starting torque in foot pound of torque per kVA of inrush. It is a good choice for reduced voltage starting of high inertia loads, but is also the most expensive reduced voltage type starter.

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-

Primary resistor or reactor-type reduced voltage starter. The motor inrush current is limited by the value of resistance or reactance placed in the primary circuit. Because starting torque is a function of the square of the voltage, if the voltage applied to the motor is only 50 percent of rated voltage, the starting torque will be reduced to only 25 percent of normal starting torque. This type of starter shall only be used with low inertia loads where the low starting torque provided is sufficient for the connected load. This type of starter provides the smoothest acceleration of the load possible and is usually the least expensive.

-

Part-winding motor starter. This requires a special motor that is wired for part-winding starting and two magnetic motor starters. It shall only be used on light or low inertia loads. It is fourth in terms of smooth acceleration of the load.

-

Wye-delta type motor starter. This type of motor starter initially energizes the motor windings in a wye configuration and then transitions (either open transition or closed transition are available) when the load approaches full speed. Because wye-delta starters only provide 33 percent of normal starting torque, this method shall only be used where the drive equipment can be started unloaded. This installation requires a special motor, and both ends of each motor winding shall be brought back to the motor starter. This type of reduced voltage starter is especially useful for long acceleration type applications such as centrifuges. Table 10-17, Comparison of Different Reduced Voltage Starters, in Chapter 10 of ANSI/IEEE 141-1993 shows a comparison of the operating characteristics of different reduced voltage starters.

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x Solid-state motor starters. Solid-state motor starters can control the starting cycle and provide reduced voltage starting for conventional ac motors. The solid-state electronics provide a smooth and adjustable acceleration rate for motor starting that limits inrush current surges and reduces sudden torque surges to the motor. Solid-state motor starters shall be considered where smooth acceleration is a must and where maximum limitation of inrush current must be achieved. Reduced voltage auto transformer-type starters shall be specified unless special starting requirements exist. Review special starting requirements with Metropolitan before selection of alternate equipment is made. The branch circuit device provided in a combination motor starter shall be selected with care. If an upstream device provides the necessary short circuit protection, then a simple disconnect switch may be sufficient. In motor control center applications, the branch circuit device must provide both the disconnect function and the short circuit protection for the branch circuit. Short circuit protection shall be provided by circuit breakers except that properly sized fuses shall be used in combination with them where current limiting protection is required. Two types of circuit breakers are available for motor branch circuit protection and each functions differently. When a branch circuit device is used in combination with a motor starter it may be selected to provide both overcurrent and short circuit protection, or only short circuit protection. The two types of circuit breakers used in low voltage motor control, magnetic-only and thermal magnetic, are discussed below. x Magnetic-only circuit breakers (MCP) are the type most often used in combination motor starters. They can only be used in combination with a motor starter because they do not provide any overcurrent protection. The NEC allows MCPs to be sized up to 700 percent of motor full-load ampere (FLA) and set up to 1,300 percent of motor FLA. In most situations, the selection of the proper MCP shall be left to the motor starter manufacturer and it should be sized so that its range of adjustment allows it to be set between 7 and 13 times motor FLA. MCPs are less expensive than thermal magnetic circuit breakers and clear short circuit currents faster. For motors 50 hp and larger, they may provide less protection than a properly sized thermal magnetic circuit

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STANDARD ELECTRICAL DESIGN PROCEDURES breaker.


x Thermal magnetic circuit breakers are also used as motor branch circuit protection. They provide both short circuit and overcurrent protection. Depending on the type of motor being protected, the NEC allows thermal magnetic circuit breakers to be sized at as much as 250 percent of motor FLA. Thermal magnetic breakers 70 amps and larger with an adjustable magnetic trip unit can be sized such that the magnetic trip assembly provides adequate short circuit protection for the motor branch circuit. Smaller breakers with only fixed magnetic trip units cannot be sized small enough so that the instantaneous trip point is between 7 and 13 times motor FLA and will not be tripped by motor running current. Where the convenience of a circuit breaker is desired but the available fault current exceeds the rating of a motor starter with a magnetic-only circuit breaker, a current limiter shall be added to the breaker to increase the rating of the assembly. A current limiter is similar in construction and characteristics to a current limiting fuse. Because circuit breakers offer more convenience, tripping of all three phases, and adequate motor protection if properly selected, they shall be used for motor branch circuit protection unless a special condition exists. Combination motor starters for 480-volt applications shall be provided with magnetic-only circuit breakers (MCPs). MCPs shall be sized in accordance with Table 2-1. 3.5.1.1 Motor Control Center. Except in those situations where only a couple motor starters are required, low voltage combination motor starters shall be grouped in motor control centers (MCC). "Motor control center" is a term that generally refers to a collection of motor control equipment and circuit breakers assembled in a series of steel-clad enclosures. Each circuit breaker and combination motor starter is individually enclosed in a compartment separated from other compartments by metal barriers. Motor control centers are available in a variety of enclosure types. The NEMA 1 enclosure is the most common, but NEMA 1 gasketed and NEMA 12 types are offered for those times when a greater degree of exclusion of dust is required. NEMA 3 and NEMA 3R enclosures can be purchased for outdoor installation. Several types of motor control centers can be purchased. They are defined as Class I Type A, Type B, and Type C; and Class II, which is furnished in Type B and Type C only. The class and type define the type

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual of wiring to be provided within the MCC. See Chapter 23 of the Switchgear and Control Handbook or a manufacturer's descriptive literature for a complete description of the requirements of each. Class I Type B wiring shall be specified for all motor control centers unless significant amounts of wiring are required between control units, and then Class II Type B wiring shall be specified. Motor control centers shall be specified with sufficient ampacity in the main bus to carry the connected load, including known future loads, and have 20 percent spare capacity. Where this criteria results in a main bus with an ampacity greater than 1,000 amps, the selection shall be reviewed with Metropolitan. The short circuit rating of the motor control center shall be greater than the fault current available at the line side terminals of the MCC plus the motor contribution, as required by NEMA ICS 2-322. The short circuit rating of an MCC is equal to the interrupting capacity of the lowest rated device in the assembly. Circuit breaker type combination motor starters are UL listed for 22,000 amps interrupting capacity (AIC). Higher short circuit ratings are available by the substitution of high interrupting circuit breakers or the addition of current limiters. Where fault currents above 22,000 amps symmetrical are available, circuit breakers with current limiters or current limiting circuit breakers shall be specified. 3.5.1.2 Control Power Transformers. Control power transformers (CPTs) shall be provided in all motor starters to provide 120-volt control circuit power. CPTs shall be provided with two primary fuses, one on each side of the transformer, and one secondary fuse on the ungrounded side of the transformer. CPTs shall be sized to carry at least 150 percent of the total connected load of the control circuit. CPTs shall not be smaller than 100 VA. 3.5.2 Medium Voltage The protection of an ac motor is a function of its type, size, speed, voltage rating, application, location, and type of service. Medium voltage motor control equipment (controllers) are rated for use on systems from 2,300 volts to 4,800 volts. Above 4,800 volts, metal-clad switchgear equipment must be used. Medium voltage motors shall be controlled by medium voltage motor starters that are specifically designed for the type of motor to be controlled and that have a horsepower rating equal to or greater than the rating of the motor. Motor starters shall be NEMA Class E-2 as described in ANSI/NEMA ICS2.

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual Each motor starter shall consist of current limiting power fuses, a contactor, instrument and control power transformers, instrumentation, and appropriate protective relay functions for the type of motor being supplied. Two types of contactors are available, vacuum and air break; the vacuum contactor type shall be selected. Motor protection is discussed in detail in ANSI/IEEE Std 242. In addition, manufacturers of medium voltage motor control equipment offer recommendations. The protective, metering, and control functions shall be provided by using a multipurpose microprocessor-based module such as the GE Multilin 469, Areva MiCom P243, or equal. Each starter shall be completely self-contained, prewired with all components in place. Where multiple starters are required in a single location, an assembly of medium voltage motor starters with a common supply bus, grounded metal barriers, and drawout mounting assemblies for each motor starter shall be provided. See the Standard Specifications Sections Catalog for more detailed requirements for medium voltage motor control equipment. 3.5.3 Adjustable Speed Drives The advancements in semiconductor devices have enhanced the design and application of solid-state drives for DC and AC motors’ speed controls. Semiconductor devices like diodes, thyristores, transistors, gate-turn-off switches (TGOs) and insulated bipolar gate transistors (IGBTs) are available with high current-carrying capacity. Microprocessor-based control systems provide reliable and highly accurate speed control. 3.5.3.1 DC devices DC motors have been the prime choice for speed control based on their adaptability to wide ranges of speed-serving duties of small to several thousand horsepower mechanical demands. Varying the armature voltage or field current can change a DC motor’s speed. 3.5.3.2 AC Drives Advances in solid-state electronics have resulted in AC drives that have high reliability and low maintenance. AC drives, which are commonly called inverters, are designed to operate standard squirrel cage induction motors. The basic drive consists of an inverter which converts the 60 Hz incoming power to a variable frequency and variable voltage. 3.5.3.3 Types of AC Drives The major types of AC drives in use today are as follows: A)

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Voltage Source Inverter (VSI). The design of VSI utilizes thyristors in the converter section and thyristors, GTOs, and transistors in the inverter section. The output voltage is controlled as six-step and is pulse-width modulated (PWM).

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B)

Current Source Inverters (CSI). The design of CSI is based on controlling motor current for the voltage frequency requirement. In the case of circuit design, the inductance of the motor plays a major part. This design can accommodate the motor to be driven at higher than the rated horsepower.

C)

Pulse Width Modulated (PWM) Inverter. The design of PWM does not change the amplitude of the controlled variable to the motor (typically voltage). They change the rms value by turning the controlled value on and off at a relatively high frequency while varying the pulse width. The switching frequency (commonly referred to as the “carrier frequency”) will determine the audible motor noise resulting from motor lamination excitation as well as how closely the PWM controller approximates a pure sine wave.

D)

Load Commutated Inverter (LCI). Unlike the first three drives which use forced commutation to turn the inverter on and off, the LCI drive uses the emf generated at the motor armature terminals to commute the thyristor inverter. The LCI drive is typically used on large horsepower synchronous motors.

3.5.3.4 Drive Power Ratings Drive controls are rated to provide a defined amount of current for continuous operation at a defined maximum ambient temperature. Controls re generally identified as one of two basic types. A)

B)

3.5.3.5 A)

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Variable torque. A variable torque control rated with a 1- minute overload capability of typically 110 percent to 125 percent of nameplate continuous rated current which is typically sufficient for variable torque loads. Constant torque. A constant torque control is typically rated with a 1-minute overload capability of 150 percent of the nameplate continuous rated current. Control Methods Volts per Hertz. In V/Hz control the volts to hertz ratio is maintained at a user programmable value ove rthe operating frequency range. It is generally applied where fast response to torque and speed commands is not required. A control using the V/Hz technique is particularly useful where multiple motors are connected to a single control.

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual B) Vector Control. A squirrel-cage motor is singly excited machine fed by connection to its stator windings, unlike a DC motor that is doubly excited through its armature and field windings. An AC vector control decouples the magnetizing flux producing current and the torque producing current to control them separately. This gives the ASD excellent steady state and dynamic performance. Very accurate speed and torque control can both be achieved. x Direct Vector Control - A direct field oriented control scheme is one that directly regulates the motor flux vector in order to produce controllable motor torque. Such a scheme employs Hall effect transducers or air-gap flux sensing windings for the measurement of the motor air-gap flux with the necessary modifications to approximate the rotor flux. The rotor flux would then be used as the feedback in the direct vector control regulator. x Indirect Vector Control - An indirect field oriented control scheme is one that interprets the motor flux vector from other parameters, such as speed or current. The two types of indirect vector drive control schemes used today are closed-loop or feedback vector control (which requires a speed feed back sensor to provide rotor position feedback) and open loop or sensorless vector (SV) control (monitors motor current instead of using a speed feedback sensor). A closed loop vector drive provides precise speed control and maximum torque from zero speed to base speed. An open loop vector drive does not have as wide a speed range as a closed loop vector drive and cannot produce holding torque at zero speed. 3.5.3.6 Line Harmonic Currents Nonlinear loads like adjustable speed drive create line harmonics when connected to the AC power distribution system. These harmonic currents are the result of non-sinusoidal current, which is a characteristic of all adjustable speed drives using diodes or silicon controlled rectifiers (CSRs) on the input. The drive input current is composed of the fundamental sinosoudial current and currents at frequencies higher than the fundamental frequency. These harmonic currents contribute to the voltampere losses: A) B) C)

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Possible interference with communication equipment Possible overheating of transformers and other branch circuit equipment Possible increased heating in motors connected acress-the-line due to copper and iron losses

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD D) Possible resonance with power factor capacitors

Electrical Design Manual

The AC input line harmonic current magnitudes vary with the design of the drive. The power distribution system impedance at the installation and the drive input design determines the actual magnitude of th eline harmonic currents. Harmonic distortion levels as stated in IEEE 519 apply at the Point of Common Coupling (PCC) between the utility system and multiple users. The harmonic voltage and current distortion values at the PCC may be reduced through several methods that include: A)

Design Techniques x Power System Design - decreasing the drive system load, as percentage of the total power distribution network load will improve harmonic voltage distortion conditions. x DC Link Choke/Inductor - an inherent design feature within some controls, provides a minimum level of harmonic reduction by changing the rate of rise of the input current.

B)

Line Impedance x AC line reactor - based upon the percent of line impedance, provides lower amplitude of harmonic currents by slowing down the rate of rise of input current pulses, similar DC link choke. x Drive Isolation Transformer - provides similar performance to an AC line reactor with the additional power quality benefit of being able to adjust the voltage magnitude.

C)

Multi-Pulse Methods/Converter Design Topologies x Phase multiplication - involves the use of a phase-shifting transformer for feeding multi-pulse control inputs. By shifting the phase relationship to various 6-pulse controls, the net effect in the power system is to create a 12-pulse circuit with cancellation of the 5th and 7th characteristic harmonics. However, this method is most effective when the motor loads are equal size and load. x 12-Pulse Rectifier - a control that utilizes a dual 6-pulse rectifier network with a phase shifting transformer for proper commutation of the dual bridges. The net effect is cancellation of the 5th, 7th, and 19th characteristic harmonics.

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual x 18-Pulse Rectifier - a control that utilizes three 6-pulse rectifier networks with a pulse shifting transformer for proper communication. This results in an improved waveform, cancellation of lower order 5th, 11th, 13th, 23rd, 25th, 29th, and 31st characteristic harmonics. x Active Rectifier Input - a control that incorporates gate controlled power semiconductors in the input rectifier stage to shape the input current waveform, to a sinusoidal waveform symmetrical to the voltage. This method of harmonic abatement is the most complex. A microprocessor controller is required for gate control of the input power semiconductors. D)

Harmonic Filters x Shunt filters – passive filters that are properly designed and for the 5th, 7th, and 13th harmonics can effectively reduce the harmonic currents in a power distribution system. x Series filters – these filters consist of a parallel LC circuit tuned to resonate a specific frequency, similar to a shut filter. The series reactor acts to de-tune other power distribution system harmonics form being trapped by the passive filter. x Harmonic injection – adaptive compensators are designed to constantly monitor the AC line current to the drive by injecting a current equal in frequency/magnitude and 180 degrees out phase to the distorted current. x Active Filters – designed primarily for multiple non-linear harmonic loads, monitoring dynamic load conditions and switching necessary VAR compensation.

3.5.3.7 Drive Application Information Complete application information is critical to the proper selection and installation of an ASD system. The specifications for an ASDsystem should include: A) B) C) D) E) F) G)

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Horsepower and torque requirements at various speeds Speed range of the load and motor Motor voltage Incoming power, voltage dips and derivations, frequently derivation, and regulating Dynamic response (Wk2) to the motor shaft, including acceleration and deacceleration time Ride-through requirements and response to momentary interruption For large motors with high-speed operation, mechanical resonance effects of gears, couplings, and flywheels

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual H) Starting and stopping cycles for emergency-management applications I) General description of the type of application including the environment in which the ASD system components must operate J) A description of additional functionality that may be met with the motor and drive only (motor temperature monitoring, ability to bypass the drive if necessary, special sequencing circuits or analog input speed reference signals to control the ASD system) K) Harmonic current and its effect on a plant’s power distribution apparatus, especially to microprocessor-based equipment and electronically sensitive instruments L) Harmonic current’s effect on mechanical output, such as torque and pulsation M) Regeneration applications 3.5.4 Power Factor Correction Power factor improvement shall be provided only when the electric utility rates include a penalty for low power factor and the projected power factor of the facility will be less than the minimum allowed within the rate. Power factor improvement shall be provided by installing capacitors on the larger motors (25 hp and larger), which are powered by full voltage starters. The capacitors shall be sized in accordance with the procedures provided in Section 2.3, Design Calculation, in this design guide, and shall not be larger than the maximum size recommended by the motor manufacturer. The capacitors shall be connected between the motor starter contacts and the overload relays so that overload relay heaters can be sized in accordance with motor nameplate currents. 3.5.5 Control Circuit Devices This section covers a broad range of devices that are found in motor control circuits. All control circuit devices shall meet the requirements of applicable NEMA ICS 2-125 Standards. Devices that contain contacts and are used in 120-volt control circuits shall have contacts with the designation A300 or A600. Only devices with contacts having the designation A600 shall be used where the control circuit voltage will be greater than 120 volts. Contacts with these designations are capable of carrying 10 amperes continuously, making a circuit requiring 7,200 voltamperes and breaking a circuit carrying 720 volt-amperes. Devices covered by this rating include momentary and maintained contact pushbuttons and control switches; push-to-test pilot lights; limit switches; snap action switches in temperature, pressure, and similar switches; and control relays.

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual All pushbuttons, selector switches, and pilot lights shall be heavy duty oiltight or corrosion resistant type. Standard duty type shall not be used. In addition, all snap action switches and control relays shall be of the quickmake quick-break type. Every motor control circuit shall contain a control switch or START/STOP pushbutton station in series with the main contactor coil to allow manual control of the drive motor. The use of two-wire and three-wire control stations is illustrated in Figure 3-6. Where the drive motor is remote from the motor starter location, the control switch or pushbuttons shall be located near the motor in either a local control panel or as a locally mounted control station. The primary function of this control device is to provide a local override of all other control devices that may exist in the control circuit. 3.6 MOTORS The subject of motors is a very broad topic and will not be dealt with in any detail in this section. The text Motor Applications and Maintenance Handbook is an excellent reference on the subject and should be reviewed for specific questions that are not addressed in this manual. In addition, NEMA standard MG 1 Motors and Generators covers the construction and testing of all types of motors and should be consulted for the general standards of the industry. 3.6.1 Basic Motor Types There are three basic types of motors that will be discussed in more detail in this section; the induction motor, the synchronous motor, and the dc motor. Most motors used within a water treatment facility will be induction motors and will fall into one of the following classifications: low-voltage single-phase, low-voltage three-phase, or medium-voltage three-phase. 3.6.2 Design Considerations There are a number of things that must be taken into consideration when specifying a motor for a specific application. Most important are the torque characteristics of the motor, its operating speed, thermal protection, and the environmental protection provided by the enclosure and the insulation system. 3.6.2.1 Motor Torque. Torque is the force that tends to produce a turning motion in an electrical motor. Torque is expressed in terms of force and distance to represent the turning moment. There are a number of types of torque that are defined in the Motor Application and Maintenance Handbook, but only the basic ones will be defined here. See Appendix G for a typical motor torque curve and associated definitions.

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Figure 3-6. Example Control Station Wiring

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x Locked Rotor Torque. This is the minimum torque developed by the motor at all angular positions of the rotor at the instant of rated-power application to the motor primary winding circuit. This torque is sometimes referred to as the breakaway starting torque. x Full-Load Torque. This is the torque necessary to produce rated speed with rated-power input. x Breakdown Torque. This is sometimes referred to as maximum torque and is the maximum torque developed at ratedpower input without an abrupt change in speed. x Accelerating Torque. This is the torque developed with rated-power input during the period from standstill to full rated speed. It is the positive torque available beyond the requirements of the load. The torque capabilities of the motor being proposed must be compared against the torque requirements of the load to verify that the motor is capable of operating the load. This is typically done by plotting the torque curve of the motor and the load torque on the same graph from zero speed to synchronous speed of the motor. 3.6.2.2 Duty Classification. Motors are classified for continuous, intermittent, or varying duty depending on their ability to drive a load: x Continuous duty refers to a load that demands operation at a substantially constant load for an indefinitely long time. Most motor applications in water treatment and pumping plants will be continuous duty. x Intermittent duty refers to a load that demands operation for alternate intervals of load and rest or load and no-load, where each interval has a specific duration. Few intermittent loads occur in water treatment and pumping plants. x Varying duty refers to a load that demands operation at loads and for intervals of time both of which may be subject to wide variations. Most motor applications in water treatment and pumping plants that are not continuous duty shall be varying duty.

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3.6.2.3 Motor Speed. Motor speed is designated in terms of revolutions per minute (rpm), and for synchronous and induction motors is directly related to the frequency of the power source. Following are several definitions that need to be kept in mind: x Full-load speed is the rated speed at which rated full-load torque is delivered with rated-power input. x Constant speed indicates that the normal operating speed is constant, or practically constant, for a specified range of torque. x Synchronous speed indicates that the motor speed is in synchronism with the frequency of the power supply. For ac motors, synchronous speed shall be found by using the following formula: Synchronous speed = (rpm)

120 x frequency (Hz) no. of poles in motor

(Eq. 3-1)

x Slip speed is the difference between synchronous speed and actual rotor speed. x Adjustable speed indicates that the speed may be varied gradually over a considerable range, but remains practically unaffected by load at each adjustment. Since the number of poles in a motor is in pairs and the synchronous speed of an ac motor is directly related to the number of poles in the motor, the motor speeds available are very limited. The synchronous motor speeds (rpm) at 60 Hz are as follows: 3,600

1,800

1,200

900

720

600

514

450

400

360

327

300

277

257

240

225

Motors are specified in terms of full-load speed, where full-load speed is the synchronous speed minus the slip speed, which will vary between 0.5 and 5 percent, depending on motor design, at full load. This term only applies to induction motors because synchronous motors operate at synchronous speed. With the introduction of adjustable-frequency controllers, it is now possible to continuously adjust the speed of ac motors because the frequency can be continuously varied.

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual A single motor can be operated at up to four different constant speeds depending on the design of the motor. A single-winding induction motor can be wound such that it can be operated at either of two speeds by reconnecting the windings within the motor. The low speed must be onehalf of the high speed. A two-winding motor can be constructed to operate at any of the normally available speeds, and the low speed does not need to be one-half of the high speed. Therefore, a single motor designed with two sets of windings, each designed for two-speed operation, would allow four operating speeds. Since a two-speed single-winding and a two-speed two-winding motor require different controllers, the type of motor to be specified shall be coordinated with the controller to be provided. 3.6.2.4 Motor Thermal Protection. Thermal protection must be provided to prevent uneconomical and excessive rates of electrical insulation system deterioration caused by excessive temperatures. Severe overheating may result in immediate motor burnout. There are a number of causes of motor heating but the ones most often encountered include: sustained overload, low or unbalanced supply voltage, high ambient temperature, loss of ventilation, failure of electrical elements, and failure of mechanical components. Several methods can be employed to protect a motor against thermal damage. In some cases, it is best to provide a combination of elements to provide protection against several possible causes. In every case, thermal overload protection needs to be included as part of the motor controller and, where high ambient temperatures are anticipated, an insulation system with a higher temperature rating should be specified. Integral overheating protection shall be provided for all motors 100 hp and larger, all motors that are driven by an adjustable-frequency drive system (AFD), and most motors that are located in wet wells or other locations where continuous cooling cannot be assured. Integral thermostat devices are adequate for small motors but larger motors shall be protected by thermistors or resistance temperature devices (RTDs). Thermistors should be used for motors 100 hp and larger at 480 volts with RTDs being used for all medium-voltage motors. The need for special protection schemes needs to be evaluated for each of the other possible causes of motor overheating. The larger the motor, the higher the operating voltage. The more critical the drive, the more likely that special protection shall be provided. 3.6.2.5 Motor Enclosures. Different types of motor enclosures are offered that provide varying degrees of physical protection from the elements for a motor (see Appendix E). Following is a brief list of those enclosures most often needed in a water treatment plant:

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x Drip-Proof Enclosure. This is an open enclosure with ventilating openings constructed so as to prevent drops of liquid or solid particles that fall on the machine from an angle of 15o or less from the vertical from entering the machine. x Weather-Protected Type I Enclosure. This is an open enclosure with ventilating passages constructed and arranged to minimize contact of rain, snow, and airborne particles with live and rotating parts. x Totally Enclosed Fan-Cooled Enclosure. This is designed to prevent free exchange of air between the inside and outside of the enclosure and includes an integral fan external to the enclosure to provide cooling. x Totally Enclosed Nonventilated Enclosure. This is designed to prevent free exchange of air between the inside and outside of the enclosure and includes no external provisions for cooling the enclosed parts. The motor is cooled by heat radiating from the surface to the surrounding atmosphere. Motors larger than 5 hp that are located in indoor dry areas may be specified to have drip-proof enclosures. Totally enclosed fan-cooled enclosures shall be specified for motors smaller than 5 hp in all locations and for larger motors located outdoors and in wet areas, except for the following two exceptions. Very small motors may also be specified to have totally enclosed nonventilated enclosures when these are the standard of the manufacturer supplying the equipment. Motors 200 hp and larger that are installed outdoors shall be specified to have weatherprotected Type I enclosures. All motors to be located outdoors and in wet and/or corrosive indoor locations shall be specified to have sealed winding insulation. 3.6.3 Low-Voltage Single-Phase Induction Motors Single-phase motors shall be specified for nonessential process loads less than 3/4 hp and in heating and ventilating (HVAC) system equipment where they are the standard of the manufacturer. Single-phase motors shall be equipped with some type of starting device to cause motor rotation. Because this starting device often includes a centrifugal switch and a capacitor, which can be points of failure, use of this motor is limited. Single-phase motors are available for operation at 115 volts, 208 volts, or 230 volts single-phase, which will allow their connection to most lowvoltage systems.

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3.6.4 Low-Voltage Three-Phase Induction Motors Three-phase induction motors shall be specified for most low-voltage process applications. Apart from the motor controller, three-phase induction motors do not require any type of auxiliary equipment to facilitate starting, and therefore they offer the highest reliability available. Lowvoltage three-phase motors are available from 1/4 to 600 hp but shall not be specified above 200 hp except in special situations. Voltage selection for motors larger than 200 hp shall be reviewed with Metropolitan. Low-voltage three-phase induction motors are classified by NEMA in accordance with five design types (Appendix F). The design types are A, B, C, D, and F, and the main difference between them is their torque characteristics. Design B motors shall be specified unless the load being driven has special torque requirements and a special motor is required. These motors are capable of being driven as either constant-speed motors by a full- voltage or reduced-voltage motor controller, or at adjustable speed by a speed-control system. An adjustable-frequencycontrolled speed drive system can be used to operate a normal induction motor, whereas a wound-rotor motor is required if a wound-rotor motor controller is to be used. Except where special circumstances require otherwise, adjustable-speed motors shall be three-phase induction type with pulse width modulated (PWM) adjustable-frequency controllers. Motors specified for operation with adjustable-frequency controllers shall be sized so that the driven load does not exceed 87 percent of the nameplate rating of the motor. 3.6.5 Medium-Voltage Induction Motors Medium-voltage induction motors shall be used for all applications where the motor size exceeds 200 hp. Medium-voltage motors may be used for smaller motors if medium-voltage motor control was provided for the existing motors to be replaced. There are some situations where synchronous motors should be selected; these applications are covered under paragraph 3.6.6, Synchronous Motors. All medium-voltage motors shall include integral overheating protection provided by resistance temperature devices (RTDs) embedded in the coils of the motor and in the bearing housings. A multichannel system shall be provided to monitor the temperature at each RTD location. A contact operation shall be provided to STOP the motor should the temperature at any location exceed a preset value.

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3.6.6 Synchronous Motors Synchronous motors are similar in construction to induction motors and require similar type controls except that, since they need to be separately excited, the control equipment is much more complex. Synchronous motors are available from fractional horsepower to many thousands of horsepower. They are typically used where large loads are operated continuously and power factor improvement is required because they can be a source of VARs when they are overexcited. There are few applications in a water treatment plant that justify the added expense of a synchronous motor and its associated controls; each potential application needs to be reviewed carefully. The synchronous motor needs to be protected for the same conditions that apply to a large induction motor. In addition, due to the characteristics of the synchronous motor, there are a number of additional types of protection required. These include pull-out protection, loss-offield protection, starting winding protection, and incomplete sequence protection. The details of these types of protection are covered by several of the reference texts. 3.6.7 Direct Current Motors There are a number of applications for dc motors in a water treatment plant. These motors offer a wide speed range with essentially stepless variation in speed setting. They are capable of being accelerated and decelerated quickly and result in very accurate speed control when set. With their associated controllers, dc motors shall be specified to drive chemical feed pumps where precise control is required. Dc motors shall be powered from the low-voltage ac power system using DC-SCR drive units. Units 5 hp and less shall be supplied power at either 120 or 240 volts single phase. 3.7 RACEWAY SYSTEMS A raceway system shall be installed to provide protection for conductors for power, control, and instrumentation circuit conductors. Raceway systems can take a number of forms, but in a water treatment facility the forms most likely to be found include conduit systems, wireways, cable trays, underground trenches, and underground duct systems. The guide specifications cover the products to be used in each system and the installation of that material. This section describes when to use the different systems, the design criteria to be used in sizing the components of each system, and identifies many of the applicable sections of the NEC.

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3.7.1 Conduit System The raceway most often used to protect conductors is the conduit. Conduit is available in a number of materials, but the ones most often used are Schedule 40 PVC, galvanized rigid steel conduit (GRS), PVCcoated galvanized rigid steel conduit, electrical metallic tubing (EMT), and liquid-tight flexible metal conduit (flex). Schedule 80 PVC and flexible metal conduit (not liquid-tight) are also used for some applications. The conduit type to be used in each situation shall be determined based on the conditions expected on the project. GRS and PVC-coated GRS offer superior physical protection and should be selected for those applications where physical damage can be expected. PVC-coated GRS and Schedule 40 PVC conduit offer resistance to corrosion and shall be selected where corrosive conditions can be expected. The properties of these conduits shall be considered in combination when selecting the conduit to be used for such applications as turning up out of a corrosive soil or passing through the interface between concrete and either the soil or a wet condition exposed to the air. In both of these situations, the superior properties of PVC-coated GRS make it the preferred choice. The galvanized coating of EMT resists corrosion well but the walls are so thin that it does not resist physical damage well. EMT shall be used in dry areas above ceilings and concealed in walls for lighting, receptacle, and HVAC circuits. Schedule 40 PVC shall be used where conduits are to be installed underground, either direct buried or concrete encased, because of their superior resistance to corrosion. Schedule 40 PVC shall also be installed abovegrade where a corrosive environment is anticipated, such as in a chemical room, and where the conduit can be protected from physical damage. Articles 344, 350, 352, 353, and 358 of the NEC contain additional information pertaining to the installation of conduit systems and shall be consulted during design. 3.7.2 Conduit Identification Conduit numbers shall be assigned to conduits. The conduit number shall be shown on equipment layout drawings, electrical conduit layout drawings, wiring diagrams, and conduit schedules. The conduit number shall be composed of the equipment number of the serviced equipment, plus a sequentially assigned number.

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3.7.3 Wireway Wireways with conduit nipples shall be used to interconnect electrical equipment where there will be a number of separate enclosures located close to each other. The wireway provides an ideal pathway between the enclosures, it provides space for tapping of conductors, if necessary, and it makes grouping of conductors from the various enclosures into conduits leaving the area very easy. Article 376 of the NEC contains additional information pertaining to the application of wireway and shall be consulted during design. 3.7.4 Cable Tray System The cable tray system is an ideal raceway system for use where frequent changes in the conductor or cable systems are expected. They have limited use in a water treatment plant where changes occur only infrequently. There are a number of rules in the NEC which must be kept in mind should the engineer choose to use a cable tray system. Article 392 of the NEC covers the installation of cable tray systems and the installation of conductors and cables in them. Single conductors shall be No. 1/0 AWG or larger and labeled for installation in a cable tray. All multiconductor cables shall also be tray cable (TC) rated to be installed in a cable tray system. In water treatment plants, cable tray systems shall be used in electrical rooms to provide convenient routing of feeder conductors between major equipment items and between the electrical room and the control room to route control and instrumentation cable. Ladder or ventilated/trough cable trays without covers permit the maximum free flow of air across cables and shall be used to route power and control cables. Solid bottom steel cable trays with steel covers provide EMI/RFI shielding protection for sensitive circuits and shall be used to route instrumentation cables. 3.7.5 Trench System The trench system offers an alternative to an above ground cable tray system or a duct bank system in substation and switching station yards where a large number of conductors and cables must be routed around the yard. The trench system may be either precast concrete sections or cast in place. A variety of trench widths and depths are available and the precast type are available with a broad range of options and accessories. Barriers shall be provided to separate conductors and cables of different systems that are routed through the same trenches.

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Trench systems shall be open bottom with a crushed rock fill to provide drainage and cable and conductor support. The trench shall be covered by removable fiberglass reinforced concrete panels. Special sections shall be provided where equipment will be expected to cross the trench system that are designed to carry traffic loads and meet the requirements of applicable portions of AASHTO H-20. 3.7.6 Ductbank System A ductbank system consists of a number of handholes and/or manholes interconnected by red concrete encased buried conduits. The conduits are grouped together and routed along a single corridor to minimize the space required for them. Ductbanks shall be constructed using Schedule 40 PVC conduit with appropriate spacers to maintain the NEC required spacing. Separate ducts shall be installed for low-voltage (600-volt and less), mediumvoltage, control, instrumentation, and communication cables. Communication duct shall have a separate handhole. High voltage duct shall have a separate manhole. Low-voltage, power, control, and instrumentation cables that run in the same manhole or handhole shall be provided with barrier in accordance with NEC. The largest ducts shall be installed at the bottom of each ductbank with all of the spare ducts being provided at the top of the ductbank. Even though different sizes of ducts may be required by the conductors and cables to be installed, the number of sizes being installed shall be kept to a minimum. Each row in the ductbank shall be the same size throughout its width and the minimum size conduit to be installed shall be 1 inch. 3.8 CONDUCTORS All conductors, regardless of use, shall be copper and shall be stranded. This section will cover both low-voltage, including conductors and cables for instrumentation and control systems, and medium-voltage wiring systems and their related appurtenances. 3.8.1 Low-Voltage Wiring Systems (600 Volts and Below) Low-voltage wiring systems shall generally consist of insulated copper conductors installed in an approved raceway system. The minimum size conductor to be used for power and lighting systems shall be No. 12 AWG. Conductors used for control circuits shall be No. 14 AWG minimum, but larger conductors may be used where control circuits are long.

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3.8.1.1 Power Conductors and Cables. Conductors used for feeders and branch circuits to process equipment shall be insulated with a crosslinked, thermosetting, polyethylene insulation and shall be UL type RHHRHW-USE. Conductors used for lighting and receptacle branch circuits shall be PVC insulated, shall have a nylon jacket, and shall be UL Type XHHW. Where conductors for power circuits are to be installed in cable trays, they shall be UL-listed as suitable for that use. The NEC does not allow single conductors smaller than No. 1/0 AWG to be installed in cable trays. Smaller feeder and branch circuit conductors to be installed in cable tray shall be multiconductor power cable rated type TC. Low-voltage conductors shall be sized in accordance with the requirements of NEC Table 310-16, as described in paragraph 2.3, Design Calculations. Conductor ampacities used in the calculations shall be based on the appropriate temperature rating for the conductor and corrected for the ambient temperature that can be expected and for the conduit fill conditions. Because many terminals used in equipment for conductors No. 1 AWG and smaller are not UL-listed for applications above 60o C, conductors No. 1 and smaller shall be sized using their 60o C ampacities. Where derating factors are used in the calculations for sizing these conductors, either 75 or 90o C ampacities, whichever is appropriate for the application, may be used in the calculation as long as the resulting ampacity calculated is equal to or less than the listed ampacity at 60o C. Terminals for larger conductors are rated for use with conductors rated 75o C. The 90o C ampacities of conductors larger than No. 1 can be used in determining the size of the conductor to be used, if: x The conductors (conduit) are being installed in a dry area; x Derating is required due to high ambient temperatures or if the number of conductors being installed in the conduit exceeds three; o x The resulting ampacity calculated does not exceed the 75 C rating of the conductor.

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3.8.1.2 Control Conductors and Cables. The minimum size conductor to be used for control circuit shall be No. 14 AWG. No. 12 AWG conductors shall be used for long circuits where additional physical strength is required. The conductors shall be PVC insulated, shall have a nylon jacket, and shall be UL type THWN/THHN/MTW. Where multiple control conductors are required between two panels or terminal junction boxes, a multiconductor control cable shall be installed. Multiconductor control cables shall be constructed using UL type THWN/THHN/MTW single conductors bound together in a single assembly with a PVC jacket. The assembly shall be manufactured in accordance with UL 1277 and shall be UL and NEC Type TC suitable for cable tray installation. Individual conductors of multiconductor control cable assemblies shall be color coded in accordance with Method 1, Table K-2 of ICEA 5-66-524. Control conductors may be installed with motor branch circuit conductors where control devices are located at or near the motor. Individual conductors shall be installed with branch circuit conductors No. 4 AWG and smaller, and multiconductor cables shall be installed where the branch circuit conductors are No. 2 AWG or larger. Where the branch circuit conductors are larger than No. 4/0 or parallel conductors are used, control conductors shall be installed in a separate raceway.

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual 3.8.1.3 Instrumentation Cables. The minimum size conductor to be used for analog signal circuits and other low voltage discrete dc circuits shall be No. 18 AWG. These conductors shall be installed as twisted shielded pairs (TSPs) and/or triads (TSTs) as may be required for the installation. A TSP shall consist of two No. 18 or larger stranded copper conductors with PVC insulation and a bare copper drain wire twisted together within a conducting shield and a flame retardant jacket. A TST shall be similar except that it shall contain three No. 18 or larger insulated stranded conductors. Instrumentation cables are available with both 300-volt and 600-volt insulation. Cables with 600-volt insulation shall be used wherever they will be installed in equipment that contains circuits that operate at above 120 volts to ground. Cables with 300-volt insulation may be used wherever physical separation will be maintained from conductors that operate at above 120 volts to ground. See the specifications for the details of construction of the instrumentation cables to be used. A TSP shall be installed from each field-located device to the associated control room-located instrument, panel, or remote terminal unit without the use of intermediate terminal junction boxes, wherever possible. The exception to this is where multiple instruments (more than five) are located close to each other, and then a local terminal junction box shall be installed to gather the single TSPs together into a multipair cable. The multipair cable shall be constructed of multiple, individually jacketed, twisted shielded pair conductors cabled together within an overall shield and jacket. Where a large number of 24-volt discrete signals have been brought together in a terminal junction box and need to be connected to the terminals of a distributed control system or similar input/output assemble for a programmable logic controller (PLC), a multipair unshielded cable may be used. All instrument cables shall be terminated with locking forked tongue lugs on numbered screw type terminal blocks. Terminal blocks shall be constructed of UL- recognized component plastic, phenolic, and have nickel-plated brass, binder head type screws.

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3.8.2 Medium and High Voltage Conductors (Above 600 Volts) Two types of insulation must be considered when specifying medium- and high- voltage conductors. They are the cross-linked polyethylene (XLPE) and thermosetting ethylene-propylene rubber (EPR) compounds. Although both insulations have similar properties and ratings, EPR is less subject to treeing in the presence of water. Therefore, all medium- and high-voltage conductors shall be shielded, shall have EPR insulation, and shall have a PVC or neoprene jacket. Conductors with insulation rated 133 percent shall be used on ungrounded and resistance grounded medium-voltage systems. Conductors with insulation rated 100 percent may be used on systems that are solidly grounded. See the specifications for the details of medium-voltage conductor construction. The ampacity tables of Article 310 of the NEC shall be used in selecting conductor sizes for medium- and high-voltage circuits but the Engineer must not forget the effects of short circuit currents on these conductors. The application of each medium- and high-voltage conductor shall be reviewed with respect to allowable short circuit current for the conductor size required and allowable temperature rise of the insulation before the short circuit protective device trips. Chapter 12, Cable Systems, of IEEE Standard 141-1993 should be consulted for additional information on this subject. In addition, several manufacturers have published data and graphs that are useful in selecting conductors that are properly sized for applications where fault currents are high. 3.8.3 Splices and Terminations As a general rule, no conductor, regardless of voltage, shall be spliced, but there are certain situations where splices and terminations will be required. This section deals with the splicing and termination of lowvoltage and medium-voltage insulated conductors. Low-voltage power conductors in lighting and receptacle circuits may be spliced using UL-listed insulated, twist-on spring connectors (wirenuts). Splices in conductors to process equipments, control elements, and instruments shall be made with approved compression type connectors. Final terminations at motors and similar equipment where removal of the equipment for maintenance can be expected shall be made with approved bolted connection. All splices and termination shall be insulated using heat-shrinkable sleeves that provide an insulation level at least equal to that of the conductor. Splices shall not be tolerated in control and instrumentation circuit conductors. Where splices are required, they shall be made on terminal strips in a junction box (terminal junction box). Control conductors and cables shall be terminated at box lug type terminal blocks rated 600 volts

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual as specified in Section 16050, Basic Materials and Methods, of Metropolitan's Standard Specifications Sections Catalog. Instrumentation conductors and cables shall be terminated using locking forked tongue lugs and screw type terminals as previously mentioned in this chapter and as specified in Section 16120, Conductors, of the specifications. Splices shall only be allowed in medium-voltage conductors where existing conductors must be extended and terminals are not available for the extension. Such splices shall be made inside of manholes or above ground pedestals using premolded deadbreak elbow and modular splice assemblies of ethylene-propylene-terpolymer (EPDM). Terminations located indoors and in motor termination boxes shall be of the factory premolded EPDM type. Terminations in pad-mounted transformers shall be of the premolded EPDM loadbreak elbow type. All other terminations of medium-voltage conductors shall be made using factory premolded and skirted EPDM type or preassembled slip-on type terminators. See Metropolitan specification Section 16120, Conductors, for additional information about splices and terminators for mediumvoltage conductors. 3.8.4 Conductor Identification All conductors on each project shall be identified by a system of unique numbers. Circuit numbers shall be keyed to the equipment to which the conductors are connected. Each conductor shall be identified at each termination point and at all accessible locations, such as handholes, manholes, pullboxes, etc. The conductor number shall be shown on wiring diagrams, wire lists, instrument loop diagrams, and panel wiring diagrams. Conductors shall be identified by approved conductor and cable tags. See Metropolitan specification Section 16120, Conductors, and Appendix H for additional information on the conductor identification system and a material specification for the tags. 3.8.5 Conductor Installation Conductors and cable shall only be installed in conduits and ducts that are properly sized, properly installed, and free from debris. Installation of large conductors and cables in long conduit or duct runs, or in conduit or duct run with multiple bend, need to be reviewed carefully to verify that they can be safely installed without damage to them. Pulling tension calculations and jam ratio calculations should be performed to determine if additional pull points or larger conduits are required.

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3.9 JUNCTION BOXES AND PULL BOXES Junction boxes and pull boxes shall be provided to facilitate the combination of multiple circuits into a single conduit and the pulling of conductors and cables. They shall be sized as necessary to accommodate the conductors and cables being installed and shall be constructed of a material suitable for the environment where they will be located. Section 16050, Basic Materials and Methods, of Metropolitan's Standard Specifications Sections Catalog covers the basic materials that are available for use. Two sizes of boxes are discussed in this section: device boxes (small boxes) used as junction and pull boxes, and boxes that must be larger than device boxes. Junction boxes shall be shown on the drawings as required in the conduit system to group conductors, terminate cables, etc. Pull boxes may or may not be shown depending on the needs of the project. Even if pull boxes are not shown, the specifications require the contractor to install them to limit the number of bends in a conduit section to not more than three 90o equivalent bends. 3.9.1 Indoor Locations Indoor locations can have environments that vary anywhere from dry to wet and can include corrosive as well as hazardous atmospheres. Corrosive and hazardous atmospheres will be discussed later in this section. The boxes used in indoor locations must be able to withstand the physical abuse they are likely to receive, stand up to the environment, and keep water out of the raceway system. Boxes used in dry areas may be manufactured of either sheet steel or cast metal. Small boxes that may be subject to physical damage shall be manufactured of cast metal, whereas larger boxes in such locations shall be manufactured of sheet steel. Small boxes located 4 feet above finished floor in lighting, and receptacle circuits and concealed boxes in all raceways, shall be constructed of sheet steel. Small boxes to be installed in damp or wet locations shall be cast metal. Larger boxes may be either cast metal, epoxy-coated sheet metal with stainless steel hardware and neoprene gaskets, stainless steel, or gasketed reinforced fiber glass with stainless steel hardware rated NEMA 4. Cast metal conduit fittings may be used as junction boxes in both dry and wet areas if the box contains no splices; large device boxes shall be used wherever splices are necessary.

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3.9.2 Outdoor Locations Boxes to be installed in outdoor locations that have noncorrosive atmospheres shall be installed using the same criteria as for indoor wet areas. Boxes shall be installed in such a way as to protect them from physical abuse either by locating them out of harm's way or installing them behind a removable barrier. Concrete pull boxes shall be installed in underground runs of conduits where the number of conduits passing through them do not justify installation of a handhole or manhole. 3.9.3 Corrosive Locations Boxes to be installed in corrosive locations shall be rated NEMA 4X and shall be manufactured of a material suitable for the corrosive environment. These boxes should be located away from corrosive materials as much as possible. Acceptable materials include 316 SST, reinforced fiberglass, and PVC. PVC may only be used in the smaller sizes. 3.9.4 Hazardous Locations Boxes to be installed in hazardous locations shall be UL-listed for use in an area with the hazard classification that exists if a standard exists. Where a standard does not exist, the boxes shall be designed to meet the requirements of NEMA 7 as a minimum. 3.9.5 Terminal Junction Boxes The term "terminal junction box" (TJB) shall be a term applied to junction boxes that contain terminal strips for the termination of either control conductors, small power conductors, or instrumentation cables. They shall be constructed using a junction or pullbox that is suitable for the area where it is to be installed and contains terminal strips that are suitable for the conductors to be terminated. See Section 16050, Basic Materials and Methods, of Metropolitan's Standard Specifications Sections Catalog for additional requirements for TJBs.

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3.10 MANHOLES AND HANDHOLES Manholes and handholes are similar in construction except for their size, but are used for different purposes. Handholes are smaller and are used as pull points and locations to redirect circuits in low-voltage and communication ductbank systems where it is reasonable to work with the conductors from above ground. Manholes are much larger and are used as pull points and places to redirect circuits in medium- voltage ductbanks and in low-voltage ductbanks where the conductors are too large to work from above the ground. Manholes are constructed with enough depth to allow a worker to climb down into it. Since a worker must be able to move within the manhole without contacting the low- and medium-voltage conductors that pass through it, the horizontal dimensions of the manhole must also be larger than that of a handhole. 3.10.1 Handholes Handholes shall be precast concrete, shall contain blockouts or knockouts on all four sides, and shall have a square or rectangular opening in the cover. The opening in the cover shall be equipped with a hinged cover that is suitable for the location where the handhole is to be installed. Handholes that will be installed in driveways, parking areas, or other areas where vehicle travel can be expected shall be equipped with covers that are rated for AASHTO H-20 loading. Handholes in other areas may have covers with a lower loading class. Handholes that are smaller than 4 feet by 4 feet by 4 feet need not be equipped with cable racks and insulators, but the contractor shall be required to provide adequate support for all conductors and cable to keep them from laying on the floor of the handhole. Handholes to be installed in areas with high groundwater shall be equipped with a single drain opening that can be either plugged or plumbed to a drain. When trying to keep the inside of the handhole dry, remember the buoyant effect that can result. It is often better to leave the opening open and allow the water level in the handhole to rise and fall with the groundwater level. In areas where groundwater is not a problem, similar handholes can be used, or handholes with no bottom are also acceptable. Handholes shall be installed in low voltage and communication system ductbank at all 90o bends, adjacent to every building and/or structure where large numbers of ducts enter the ductbank system, and as necessary to limit pulling tension required for installation of conductors and cable to within safe limits.

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3.10.2 Manholes Manholes shall be precast concrete, shall contain blockouts or knockouts on all four sides, and shall have a round opening in the top. The opening in the top shall be equipped with a cast metal cover that is suitable for AASHTO H-20 loading. The manhole shall be a minimum height of 6-1/2 feet clear inside so that a person can stand full erect within the manhole. Manholes shall be equipped with heavy duty inserts and cable racks to provide support for conductors and cables that pass through them. All conductors and cables shall be trained around the perimeter of the manhole and shall be tied into place with suitable wire ties or similar banding material. Manholes shall be equipped with a depressed area for installation of a portable sump pump. Remember, in high groundwater areas the buoyancy of the manhole may be sufficient to lift it out of the ground; therefore, it may be necessary to provide a drain in the bottom of the manhole to allow the level of the water in the manhole to rise and fall with the groundwater level. Manholes shall be used in all medium-voltage ductbank systems and in low-voltage ductbank systems where the size of the conductors makes it impossible to work with them from above the ground. They shall be installed at all 90o bends and as necessary to limit the pulling tension required for conductor or cable installation to within safe limits. Should handhole or manhole spacings greater than 300 feet be desired or 90o bends be necessary, pulling tension calculations shall be performed. 3.11 LIGHTING SYSTEMS In this section, three different lighting systems are discussed. The first provides general illumination for visual tasks that are necessary in and around a facility, the second is an emergency/standby system to provide minimum illumination of means of egress so that safe exit from an area is possible should normal power fail, and the third is exit signing. All three lighting systems are not always necessary; building codes and common sense dictate when the second and third types of systems are necessary.

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3.11.1 General Illumination Lighting for general illumination can be provided by a variety of sources depending on the visual tasks that are anticipated, the lighting levels required, the mounting height of the luminaires, and the frequency of use of the lighting system. Illumination should be provided by the source that provides the highest light output (lumens) per watt of input power (efficacy) that can be used, providing reasonable color rendition for the visual tasks in the area. Fluorescent lamps shall be the preferred source in indoor locations, and high-pressure sodium (HPS) lamps shall be the preferred source in outdoor and high bay indoor locations. Fluorescent lamps are available in several types and each has very specific characteristics. Because of their long life expectancy, the fluorescent lamps most often used are the 48-inch, 40-watt (34-watt energy saver) preheat rapid start; the 96-inch, 75-watt (60-watt energy saver) slim line; and the 96-inch, 110-watt (95-watt energy saver) high output lamps. They are available in several color classifications, but the only ones that will be considered here are the cool white and warm white classifications. Although warm white lamps produce a higher light output, cool white lamps are recommended for most applications because they provide truer color rendition and thus better visibility. Warm white may be selected for industrial type applications where color rendition is not important. HPS lamps are available in a number wattages and are suitable for burning in any position. Even though their color rendition is not equivalent to that of fluorescents, their increased efficacy (lumens per watt) and their longer life make them the best choice for outdoor and hard to relamp indoor areas. One characteristic of all high- intensity discharge lamps (mercury vapor, HPS, and metal halide) is that they require a warm-up and restrike time, they are not immediately on as is a fluorescent or incandescent lamp. The warm-up time for a HPS can be as much as 3 to 4 minutes, during which time the light output is greatly reduced. The restrike time for a HPS is usually 1 minute or less. Where immediate light output is necessary on re-energization, an auxiliary quartz lamp can be provided by some luminaire manufacturers. Other lamps that may be used include the incandescent, the mercury vapor, and the metal halide or multivapor lamps. The incandescent has very low efficacy and short life, but it is on immediately when energized and is very low cost. It has applications in out-of-the-way places that are not visited frequently, and where low temperatures or hazardous environments make the selection of other sources difficult. Mercury vapor and metal halide could be applied in the same areas where HPSs have

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual been recommended. Each has advantages and disadvantages, which will not be discussed here. When used, incandescent lamps shall be extended service, inside frosted type unless clear lamps are required to meet specific design requirements. 3.11.2 Recommended Illumination Levels The Illuminating Engineering Society (IES) has published a handbook that contains recommended illumination levels for nearly all situations. Table 3-2 is based on the recommendations of IES but is abbreviated because of the need to use more general area classifications that can be applied to a water treatment plant or pump station. Footcandle levels recommended are only approximate, and judgment must be exercised when selecting appropriate levels and making the calculations. In some instances the lighting level indicated only applies to a small portion of a room or area, and it may be best to provide task lighting (Figure 2-4) at the higher level and use a lower level for the rest of the area. 3.11.3 Lighting System Design The design of lighting systems for Metropolitan’s water treatment plants, pump stations, and administration and maintenance buildings shall be in accordance with California Code of Regulations, Title 24, State Building Code. The Code provides performance and perspective compliance approaches for achieving energy efficiency in building lighting systems. 3.11.4 Luminaires There are too many companies that manufacture luminaires to list them or the types of luminaire that they manufacture. In this section, some of the general types of luminaires available will be discussed and recommendations for their use will be made.

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Table 3-2. Recommended Illumination Levels Task/Area

Footcandles

Office/Lab Areas General Close Work

50 100

Control Room

50

Process Areas

30

Storage Areas/Active

20

Storage Areas/Inactive

10

Outdoor Areas Filters Pump Stations Storage Areas Walkways Roadways

5 10 5 2 1

3.11.4.1 Fluorescent. Fluorescent luminaires used indoors shall be one of four basic types: x x x x

Recessed type with a lens; Surface type with a lens; Open-chassis type; Enclosed and gasketed.

All lenses shall be specified to be 100 percent clear acrylic. Recessed fluorescent luminaires with a prismatic acrylic lens shall normally be used in office areas, and lab areas. The luminaire specified must be coordinated with the type of ceiling being installed, because the luminaire to be recessed in a lay-in ceiling cannot be installed in a plaster board ceiling and vice versa. Two-lamp luminaires are preferred but three- and four-lamp luminaires shall be used where higher footcandle levels are required and/or two-level switching is desired. Where threeand four-lamp luminaires are installed in office areas, two-level switching shall be provided. Surface-mounted fluorescent luminaires with a lens may be substituted for recessed luminaires in areas where plasterboard ceilings are being installed. In areas that contain equipment having video display terminal (VDT)

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual screens, special care needs to be taken in selecting the lighting units to be used. High-angle brightness, better known as glare, must be controlled to avoid discomfort and fatigue. Proper selection of lighting units can substantially reduce this brightness and thus improve the work environment. Lighting control systems that utilize a parabolic louver assembly of preanodized specular low-iridescent aluminum, Lithonia OPTIMAX, or equal, shall be used in all areas where VDT screens will be used. Open-chassis fluorescent luminaires shall be specified for all industrial type areas in the plant where moisture is not a problem if they can be mounted at 15 feet or less. Higher mounting heights result in difficulties in relamping and the need for higher wattage luminaires. Again, two-lamp luminaires are the preferred type. Where more lamps are required to provide the footcandle levels required, higher wattage lamps should be considered. Open-chassis luminaires with reflectors shall normally be used. Where the luminaires are to be suspended, a minimum of 10 percent uplight shall be provided. In situations where surface mounting is necessary, no uplight is required and an open-chassis luminaire without the reflector may be used. All open-chassis luminaires specified shall be heavy duty type. Enclosed and gasketed luminaires shall be specified for damp and wet locations. They shall be UL-listed as suitable for the type of area that they will be installed in. Luminaires shall be manufactured of molded, highimpact resistant ABS plastic or reinforced fiberglass with a diffuser of highimpact resistant acrylic. 3.11.4.2 High-Pressure Sodium. High-pressure sodium (HPS) luminaires installed indoors shall be either open or enclosed and gasketed as best suits the needs of the area where they are to be installed. Open luminaires shall be installed in dry low and high bay areas where they will be suspended and uplight is required. They shall be installed in areas where the ceiling height exceeds 15 feet. Enclosed and gasketed HPS luminaires shall be installed in all damp and wet areas where the mounting height exceeds 12 feet. Luminaires shall be installed suspended and shall be constructed using an acrylic or glass refractor that totally houses the lamp. High-pressure sodium lamps shall be used for all lighting applications outdoors except where decorative lighting is to be provided at the entrances of administration buildings. Security lighting shall be provided on the outside of buildings and at entrances by wall-mounted HPS luminaires that use a prismatic glass or acrylic refractor to direct the light over a broad horizontal area. Each

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual luminaire shall put a minimum of 2.25 footcandles of light on the ground within a space of at least 10 feet in front of and at both sides of the luminaire when it is mounted at 10 feet above final grade. Illumination shall be provided at parking areas and on roadways by polemounted luminaires. Mounting heights shall not exceed 25 feet, and lamp size shall be 150 watt. In most situations, IES Type II luminaires will provide the best illumination on roadways whereas IES Type IV or V luminaires provide the best lighting for parking areas. Parking area and roadway luminaires shall be wired for operation at 480 volts if the voltage is available. 3.11.5 Emergency/Standby Lighting For the purposes of this section, the term "emergency lighting" shall mean those lighting systems that are required by NFPA 101 for the protection of human life when the normal power supply fails. The term "standby lighting" shall mean those auxiliary lighting systems that are not required by code but are required for safety reasons should the normal power supply fail. The same equipment shall be used for both lighting systems. Emergency/standby lighting needs in office, lab, and control room areas shall be provided by either recessed emergency lighting units or emergency lighting units that are supplied integral to the fluorescent luminaires. In either case, sufficient units shall be installed in all areas to provide adequate egress lighting for all occupants in the building. Units supplied shall provide a minimum of 90 minutes of light as required by UL 924. Emergency/standby lighting needs in enclosed process areas of the plant shall be provided by 12-volt unitized lighting units. At least one unit shall be installed in each area where motors or other process equipment exist and one unit shall be installed in each electrical room that houses switchboards, unit substation, or motor control centers. Lighting units may also be installed in other areas where the exitway may be blocked by equipment or materials and a hazard may exist. Each lighting unit shall be located to provide maximum illumination on the normal exitway. The NEC requires that all unit type emergency lighting systems be supplied power from the circuit that normally supplies the lighting in the area where the unit is to be located. Where more than one circuit supplies the area, the one that supplies the largest part of the traveled area shall be selected as the source of power.

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3.11.6 Exit Signs The Life Safety Code, NFPA 101, that defines the need for exit signing and lighting contains no requirement that would require exit signs in most buildings of a water treatment plant. There are some locations, however, where exit signs should be provided. Exit signs and lighting shall be provided in the administration building where the public and persons unfamiliar with the building may have access. Exit signs shall provide adequate direction to the exits. Rooms that have a single door that does exit to the outdoors need not be equipped with an exit sign. In addition, process buildings that contain multiple rooms so that the means of egress is not obvious shall be equipped with exit signs to direct a person to the nearest exit. All exit signs shall be electrically powered and shall contain an integral battery and low-voltage lamps to provide uninterrupted illumination should the normal power supply fail. 3.11.7 Controls Controls for lighting systems shall be designed to meet the needs of the space where the lighting system equipment is to be installed. Areas that will require illumination 24 hours per day shall be provided with switching duty circuit breakers and no local switches. In all office and process areas where illumination is not required continuously, provide a separate switch for each room. Where large rooms are encountered, at least one switch shall be provided for each two 20-amp lighting circuits. In office areas where lighting requirements will vary depending on the task at hand, dimmers, two-level switching, or occupancy lighting control sensors shall be provided to maximize energy savings. All outdoor lighting circuits shall be routed through a photocell or photocell controlled contactor to assure that they will be OFF when not required. Where outdoor lights are controlled by photocell controlled contactor, a three-position switch shall be provided so that they can be turned on for testing. In some pole-mounted lighting applications, an individual ON/OFF switch shall be installed on each pole of the lighting fixtures.

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STANDARD ELECTRICAL DESIGN PROCEDURES 3.12


LOW VOLTAGE POWER DISTRIBUTION

3.12.1 Voltage Selection Low-voltage power for lighting, receptacles, and miscellaneous power needs shall be distributed at 208Y/120 volts unless some other power need dictates a different voltage. Low-voltage power shall be supplied by installation of 480-208Y/120-volt, three-phase dry-type transformers located at each load center. Instruments shall be powered from a separate supply transformer and panelboard unless their number is very limited and the low-voltage power panel is connected to no loads that can be expected to generate harmonics back onto the bus. The instrument power supply transformer may be a 480-120/240-volt, single-phase transformer. 3.12.2 Panelboards Panelboards shall be installed as necessary to provide power to the 120-volt, single- phase and 208-volt, single- and three-phase loads shown on the drawing. Branch circuit breakers shall be thermal-magnetic type and sized in accordance with applicable paragraphs of Articles 210, 220, 225, and 430 of the NEC. Where Article 220 allows the use of demand factors, they shall be used with caution. Demand factors may be used for feeder and transformer sizing calculations but not branch circuit calculations. Where more circuits are required than can be provided by a single panelboard, provide a subfeed breaker in the panelboard supplied by the transformer to supply a second panelboard. The second panelboard may be located remote from the first panelboard. All panelboards supplied from a transformer shall have a main circuit breaker (transformer secondary breaker) that has been sized in accordance with the National Electrical Code (see paragraph 2.3.7 in this manual for sample calculations). The load on 20-amp branch circuits that supply lighting and receptacles must be limited to 80 percent of the rating of the branch circuit protective device, a 20-amp molded case circuit breaker per Article 210 of the NEC, because lighting and receptacle loads must be considered "continuous." It is recommended that the load on these circuits be limited further to 1,800 VA to limit voltage drop on these circuits. Branch circuit breakers for instruments, instrumentation panels, and so on where the exact load is unknown but is small in magnitude shall be sized at 15 amps to allow installation of multiple conductors in the same conduit. (Number of conductors limited by derating required by Article 310.15(B)(2) of the NEC.) In addition, these circuits often pass through an

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual instrument panel and become No. 14 AWG control conductors. A separate branch circuit shall be provided for each instrument and instrumentation panel unless several instruments are located at the same location, are all associated with the same flow stream or process, and monitor different parameters. In the above case, a toggle switch shall be located adjacent to each instrument to disconnect it from the branch circuit. Branch circuits for heating, ventilating, and air conditioning equipment rated 120 or 208 volts shall be supplied power from the lighting and power panelboards. Branch circuit protective devices shall be rated 15 amps unless a larger size is required to supply the load. The Engineer shall make an effort to group circuits that perform a common function together within a panelboard (e.g., all lighting together, all receptacles together). In addition, three- and four-wire branch circuits should be shown on the drawings wherever they are appropriate to minimize the amount of conduit that is required. These circuits should be connected to adjacent circuit breakers in the panelboard. Each panelboard shall be provided with a minimum of 20 percent spare breakers corresponding in size with the breakers being used. 3.12.3 Convenience Receptacles Convenience receptacle outlets shall be located throughout each facility to provide a ready power supply for portable tools. These receptacles shall be located such that no item of process equipment is located more than 40 feet from a receptacle whether inside or outside of a building. Additional receptacles shall be provided in areas where portable tools may need to be used and where the above criteria does not require one in the area. These receptacles shall all be in addition to receptacles that may need to be provided for connection of portable process equipment. Inside of the administration building, maintenance buildings, etc., which are being designed primarily for the use of personnel, coordinate the location of receptacles with the needs of the design architect. In office areas, provide outlets on at least three walls. In laboratory areas multiple outlets shall be located at work stations; coordinate these locations with the laboratory designer. Duplex receptacles shall be NEMA configuration 5-20R and shall be rated 20-amp, two-wire, three-pole grounding type unless requirements dictate otherwise. All receptacles shall be installed in boxes as described in paragraph 3.9. Receptacles located outdoors or in locations subject to washdown where they cannot be protected by mounting height (4-foot

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual minimum above finished floor) shall have a weatherproof cover. Ground fault interrupter type outlets shall be installed in all outer locations and locker rooms and bathrooms where personal hygiene items may be used. Receptacles to be installed in underground structures and in areas where a corrosive atmosphere can be expected shall be manufactured of corrosion-resistant materials. 3.12.4 Hazardous Area Receptacles Receptacles to be installed in hazardous locations shall be of the type suitable for use in classified areas in accordance with Article 500 of the NEC and shall be UL approved. 3.12.5 Power Receptacles Plugs and receptacles specified for use on Metropolitan projects shall meet applicable NEMA and UL standards and shall be selected from Figure 3-7.

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STANDARD ELECTRICAL DESIGN PROCEDURES 3.13 GROUNDING


3.13.1 General Electrical circuits, equipment, and equipment enclosures shall be bonded and grounded as required by Article 250 of the NEC. All process equipment and structures subject to potential and current flow due to lightning, static accumulation, or other abnormal conditions shall be grounded by two ground connections. References to be used in designing grounding systems shall include the following: x NFPA 70--The National Electrical Code; x ANSI/IEEE Standard 80--IEEE Guide for Safety in AC Substation Grounding; x IEEE Standard 142--IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems. Three types of grounding are discussed in IEEE Standard 142: system grounding, equipment grounding, and static and lightning protection grounding. The following sections will cover grounding of both plant electrical systems and substation grounding. 3.13.2 System Grounding Electrical distribution systems can be either ungrounded (no intentional ground) or grounded (intentionally grounded). For the purposes of this manual, a grounded system shall be a system of conductors in which at least one conductor or point is intentionally grounded, either solidly or through an impedance. The basic reasons for system grounding are the following. x To limit the difference of electric potential between all uninsulated conducting objects in a local area; x To provide for isolation of faulted equipment and circuits when a fault occurs; x To limit overvoltages appearing on the system under various conditions.

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3.13.2.1 Low-Voltage System Grounding. Low-voltage 480/277 and 208/120-volt, wye-connected three-phase and 120/240-volt, single-phase transformers shall have their neutral solidly connected to ground. This ground connection shall be of sufficient size and low enough impedance to effectively ground the low-voltage distribution system. 3.13.2.2 Medium-Voltage Grounding. Systems 2.4 to 12 kV shall be low-resistance grounded. Installation of the ground grid required shall be calculated using measured soil resistivities. The system grounding resistor shall be sized to allow sufficient ground current to flow to provide immediate and selective clearing of the ground fault. The zero sequence current transformer method shall be used to monitor for ground currents because of their increased sensitivity over a residual scheme using the high-ratio phase current transformers. 3.13.3 Grounding Electrode Systems and Grounding Grids A grounding electrode system shall be provided for all premises' wiring systems as required by the NEC. The grounding electrode system shall be used for ground of the neutral of the low-voltage power supply and the equipment ground conductors. A grounding grid shall be provided in substations and at low- and medium-voltage transformers and switchgear located outdoors to provide equipment grounding, system grounding, and to minimize step and touch potentials. The NEC permits the following to be used as grounding electrodes: x x x x x x

Metal underground water pipes Metal frame of the building or structure Concrete-encased electrode Ground ring Rod and pipe electrodes Plate electrodes

However, because of galvanic action between buried steel pipes and other nearby dissimilar metals, Metropolitan does not use buried large diameter steel pipes in its distribution system as grounding electrodes. 3.13.3.1 Service Entrance Grounding. Each power supply system shall be connected to a grounding electrode system meeting all requirements of Article 250 of the NEC. Each item within the system shall be bonded together by a bonding conductor sized in accordance with the requirements of the NEC. Where made electrodes are included in the grounding electrode system, they shall be 5/8-inch by 10-foot (minimum) copper-plated steel rod (copperweld or equal).

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3.13.3.2 Transformer Grounding. A grounding grid shall be installed at each transformer or switchgear assembly located outdoors. Where soil resistivity is measured, a complete grounding system design can be prepared. It is often sufficient to determine the approximate needs of the grounding system, install a system based on tables that are available, and then verify that the system is adequate. Using the latter method of approximation, the following grounding system should be adequate in areas where soils with reasonably low levels of soil resistivity are present. Supply transformers (pad-mounted or unit substation type) 1,000 kVA and smaller shall be provided with a minimum of two No. 2 bare copper ground connections to a ground mat constructed under and around the transformer. The ground mat shall be constructed of No. 2/0 bare copper conductors and copper clad steel ground rods in sufficient quantity to result in a measured resistance to ground of 1 ohm. For larger transformers, the entire grounding system, including the connections to the transformer, shall be No. 2/0. Where high resistivity soils are encountered, a complete grounding system design shall be performed using procedures contained in IEEE Standard 80. 3.13.3.3 Substation Grounding. A grounding grid system designed in accordance with the requirements of IEEE Standard 80 shall be installed in every substation. The soil resistivity shall be determined by field measurement, and using that data, a grid system shall be designed to keep step and touch potentials within safe limits. The grounding grid shall be constructed of copper-plated steel rods 3/4-inch by 10-foot driven full length into the ground and bare stranded copper or copper-coated steel conductors. The minimum conductor size used shall be No. 2/0 AWG, but larger conductors shall be used where high fault currents are expected. Smaller conductors may be used to connect noncurrent carrying equipment to the grid; these must be sized based on the fault current they could be expected to carry should a fault occur. All underground connections shall be made with thermoweld process. Bolted connections may be used abovegrade and shall be used at equipment and structures to be grounded. Because copper and copper-plated steel form galvanic cells with buried steel pipes and conduits, the design of the substation grounding system must be coordinated with other designs to minimize the effects of corrosion.

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3.13.4 Equipment Grounding The NEC requirements for equipment grounding are covered in Article 250. In Metropolitan-owned premises, all noncurrent carrying metal parts of fixed equipment likely to become energized shall be grounded. The equipment grounding connection shall be provided by an equipment grounding conductor sized in accordance with Table 250-122 of the NEC routed with the phase conductors. Use of the raceway system for grounding is not acceptable, but all metallic segments of the raceway system shall be bonded to the equipment grounding conductor installed in it. 3.13.5 Instrumentation and Computer Grounding Each piece of equipment shall be connected to the equipment ground point at the electric service equipment by an equipment ground conductor run with the branch circuit conductors to provide the equipment ground required by the NEC. Where isolated grounding type receptacles are used, the requirements of NEC Section 250.146(D) shall be applied. A dedicated grounding conductor connected directly to the equipment grounding conductor terminal of the applicable derived system or service may be required in some instrumentation and computer grounding applications. 3.13.6 Lightning Protection System Grounding Even though southern California is in an area of relatively low thunderstorm activity, grounding for lightning protection is still a subject that should be dealt with. NFPA 78 The Lightning Protection Code and IEEE Standard 142 both deal with the grounding requirements of a lightning protection system. The need for a lightning protection system is a separate subject and will not be addressed here. Where a lightning protection system is installed on a building or structure, its grounding system shall be installed separate from the electrical system ground, but the two shall be interconnected to provide a common ground potential. 3.14

EMERGENCY AND STANDBY POWER SYSTEMS

3.14.1 General Because emergency and standby power systems both use the same equipment and often serve the same purpose, they are both discussed in this section. For the purposes of this manual, the following definitions of emergency power and standby power systems will be used: x Emergency power system. An independent reserve source of electric energy that, upon failure or outage of the normal

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual source, automatically provides reliable electric power within a specified time to critical devices and equipment, of which failure to operate satisfactorily would jeopardize the health and safety of personnel or result in damage to property. x Standby power system. An independent reserve source of electric energy that, upon failure or outage of the normal source, provides electric power of acceptable quality and quantity so that the user's facilities may continue in satisfactory operation. To put it another way, emergency power systems are those required by law or code that are intended to provide safety of human life. Standby systems are those that are required for continuous operation of a plant or a process should the normal source be interrupted; they are usually installed by user choice. The NEC, however, defines two types of standby systems: the legally required and the optional standby systems. The legally required standby systems are those that are required by local, state, federal, and other codes to supply power to facilities where interruption of normal electrical supply could create a hazard or hamper rescue or fire fighting operations. ANSI/IEEE Standard 446--IEEE Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications, is an excellent reference on the subject of emergency and standby power systems. 3.14.2 Emergency Power Systems Emergency power systems shall meet all applicable requirements of Article 700 of the NEC. Where large amounts of emergency power are required, the need shall be supplied by an onsite diesel engine driven generator. Where emergency power is only required for emergency lighting and egress illumination, unit equipment as defined in Article 700 shall be used. 3.14.3 Legally Required Standby Power System Legally required standby systems shall meet all applicable requirements of Article 701 of the NEC. Where large amounts of power are required, diesel driven engine generators shall be installed onsite. Lighting requirements shall be provided by unit type equipment as defined in Article 700 of the NEC.

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3.14.4 Optional Standby Systems Standby power supply equipment shall be installed to provide an alternate source of power for critical control and monitoring functions, and processes that, when stopped during any power outage, could cause discomfort, serious interruption of the process, damage to the product or process, or the like. Optional standby systems shall meet all applicable requirements of Article 702 of the NEC. Lighting requirements shall be provided by unit type equipment as defined in Article 700 of the NEDC. An interruptible power supply system shall be provided for all computerbased control and monitoring equipment that may not have integral battery backup capability. 3.14.5 Engine Generators Engine generators are the most often used source of onsite emergency or standby power. They can be diesel, natural gas, gasoline, or even propane powered. To be used as an emergency or legally required standby power supply, the NEC requires onsite storage of sufficient fuel for 2 hours of full load operation; therefore, natural gas engines are not often used. In addition, due to fuel volatility nature, gasoline engines are seldom used except in very small sizes. Synchronous generators shall be used for all applications. 3.14.5.1 Diesel Engine Driven Generator. The diesel engine driven generator is the preferred source of emergency and legally required standby power because of its low first cost. For optional standby power, the natural gas engine driven generator should be given first consideration due to its cleaner burning and longer run time between maintenance. Gasoline engine driven and propane engine driven generators should not be used unless other sources of fuel are not available.

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3.14.5.2 Generator Ratings. Engine generators are available in ratings from less than 1 KW to several thousand KW, with both diesel and natural gas being available in most ratings. 3.14.5.3 Generator Sizing. Sizing of the engine generator shall be based on the needs of the anticipated connected system electrical load and shall take into account the starting requirements of the larger motors on the system. Generator sizing computer software available from most manufacturers shall be used to make the initial selection and then the generator manufacturer shall be consulted to verify that proper generator selection has been made. Selection shall be made once a complete list of loads and their sequence of application has been completed. It must be remembered that either one large motor or a number of smaller motors that are equal in total horsepower and are started simultaneously will have the same impact on the sizing requirements of the generator. If there are several motor loads that must be started immediately when the generator is connected to the load bus, each motor starter should be equipped with a time delay relay so that they can be automatically sequenced on, thus limiting the initial inrush. This will allow the generators to be sized more closely to the actual load requirements. 3.14.5.4 Considerations for Load Types. Special consideration must be given when sizing a generator when the electrical system being supplied includes loads such as adjustable frequency drive systems, uninterruptible power supplies, and similar solid state power equipment. 3.14.6 Unit Equipment Unit type emergency lighting units shall consist of a sealed lead acid or lead calcium battery, two 6-watt (minimum) lamps, a battery charger, and appropriate indicating lights and test switches all contained in a single, compact case. The unit shall meet all applicable requirements of NEC Article 700.12(F) and NFPA 101. Unit equipment shall be installed as required to provide egress lighting. Units shall be powered from the branch circuit that supplies normal lighting in the area where it is to be installed as required by Article 700.12(F) of the NEC. The connection to the branch circuit shall be made ahead of all local switches.

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3.14.7 Computer Power Systems Power shall be supplied through uninterruptible power supplies (UPS) to computer systems and microprocessor-based equipment such as remote terminal units (RTUs) and programmable logic controllers (PLCs) that have volatile memories. The UPS provides conditioned power to the equipment during normal operation and provides uninterrupted standby power should the normal source fail. Where multiple units are located in close proximity to each other, a single large UPS system shall be specified. Where the equipment is dispersed, multiple smaller UPSs shall be specified. Batteries supplied with UPS systems shall be of the low-maintenance type specifically designed for use with UPS modules. 3.15

SPECIAL SYSTEMS

3.15.1 Plant Communication System A complete plant communication system consists of a telephone system and a paging system. The objective of the plant communication system is to locate people within the plant and to communicate with the world outside the plant. The operation of the plant will be simpler and the design easier if these systems work together. It is important to get the users' early input to the communication system design. The objective of this section is to point out the steps to be followed to design a communication system for a medium to large water treatment plant. For smaller plants, which may not require paging systems, it is usually advisable to have the telephone system supplied by the local telephone company. 3.15.1.1 Telephone System. The engineer/designer should give detailed attention to how the telephone system should work; as noted below, this does not mean that a detailed design is necessary. The first option to consider in getting the users their preferred type of telephone system is to exclude it from the design package or include it as an allowance. The reasons for this are: x Leaving the telephone system selection to installation time will get a more up-to-date system. Telephone systems are changing rapidly. The telephone systems available at design time may have all been replaced with significantly changed models by the time the contractor places an order. x Putting the telephone system selection in the competitive

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual bidding process will result in the users getting the system they want at a reasonable price. The engineer/designer should have enough knowledge to assist the users with the selection. x Telephone system suppliers are generally willing to work closely with contractors so that coordination of an activity that occurs outside the contract should be no problem. The contractor shall be responsible for any claim that will occur during such coordination activities with the telephone system suppliers. Check on the cooperation offered by the suppliers in the local area. x Getting design information from a telephone system supplier will be difficult. The telephone industry is presently order driven; most suppliers will provide little information about their system, beyond sales brochures, until they have a purchase order. If the telephone system is going to be included in the design package, design around a specific system. The system supplier shall be responsible for the complete installation. Since NEC requirements on telephone installations are changing more rapidly than the code revision cycle, this will allow the latest installation methods to be used. It will also avoid having the engineer/designer act as merely a pass-through for vendorsupplied information. With the design included in the documents, it is important to get as much input from the user as is available. Find out if the user currently has any telephone systems installed that they especially like or dislike. How heavily will the system be used? How many options do they want? How much complication are they willing to put up with to use these options? The engineer/designer will need to determine the following before beginning the design: x Local phone company contact, policies on interface with private exchanges, and requirements for service (e.g., who supplies raceway, where does it go, and what size?); x Number of stations that are active (in place), equipped (can be made active by adding a phone set), and wired future (with addition of future switch modules); x Number of and configuration of paging zones;

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual x Features and options desired (see specification and manufacturer's current literature); x Location of telephone switch, attendant's console, and telephone sets; x Atmosphere (dry, wet, hazardous) at every point that a piece of telephone equipment will be installed. The engineer's/designer's tasks are then to: x Select a system that will meet the users' requirements; x Modify the specifications so that they reflect the users' preferences, the equipment available from the selected supplier, and result in a biddable document that several reputable suppliers can meet; x Locate the telephone switch and distribution frame (with assistance from selected supplier) and provide more than sufficient power to this area; provide about twice the number of receptacles that the telephone system supplier requires; x Provide a ground bus in the vicinity of the distribution frame connected to a grounding electrode and the plant grounding system; typically this bus would be 1/4-inch by 2-inch copper (check with the system supplier); x Locate a telephone terminal box in each building that will have a phone set and connect these boxes back to the building that contains the telephone switch by large empty conduits; x Locate a telephone outlet near each point where a phone set is to be installed. 3.15.1.2 Paging System. Paging systems are of two types: public address or hand-held units. The choice will depend on whether you need to locate a few people or anyone that happens to be on site. Hand-held units have the advantage of rarely being out of range while on the plantsite; their disadvantage is that the pager has to be carried and it cannot (or only with great difficulty) be tied into the telephone system. The engineer/designer must locate an amplifier in each building where paging will be required, provide an empty raceway from the amplifier to the telephone terminal cabinet, provide a receptacle near each amplifier,

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual and provide a conduit system between the paging system amplifier and the paging speakers for installation of conductors by the communications system supplier. Paging speakers shall be located on the drawings as required to provide coverage of areas where process equipment are located. 3.15.2 Fire Alarm System Fire alarm systems at industrial facilities are provided in facilities where several people are consolidated in one area and in facilities where there is a high fire hazard. Since most industrial facilities are not open to the public and are staffed by personnel knowledgeable of the process and of the hazards associated with the process, extensive fire alarm systems are not usually required. 3.15.2.1 Building Occupancy. The following buildings shall be provided with fire alarm systems: x All industrial occupancy buildings, unless the total capacity is under 100 persons and fewer than 25 persons are above or below the level of exit discharge (NFPA 101 28-3.4.1). x All business occupancy buildings where (a) the building is two or more stories in height above the level of exit discharge, (b) the occupancy is subject to 100 or more occupants above or below the level of exit discharge, or (c) the occupancy is subject to 1,000 or more total occupants (NFPA 101 26-3.4.1). x Underground structures in which the story is below the level of exit discharge, except where the story has at least two sides with at least 20 square feet of opening above the grade level (NFPA 101 30-1.3.4). x Windowless structures without grade level doors, access panels, or windows on two sides of the building (NFPA 101 30-1.3.5). 3.15.2.2 High Fire Hazard. Sources of fire hazard at water treatment plants include gases, some chemicals, and combustible dusts. Gases used for laboratory analysis (e.g., hydrogen, oxygen), unit processes (e.g., chlorine, ozone), and welding operations may provide flammable/explosive conditions when acting alone or mixed with other substances. Chemicals or combustible dusts (e.g., carbon, potassium permanganate) used in various unit processes may be combustible or cause potential flammable and explosive conditions.

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STANDARD ELECTRICAL DESIGN PROCEDURES MWD Electrical Design Manual Mitigation of fire hazards or potential ignition sources is best achieved by physical separation of reactive chemicals and ventilation. Fire alarm systems are required in the following areas: x Laboratory buildings if a fire may not, of itself, provide adequate warning to building occupants (NFPA 45 4-5.1). x High hazard occupancy, operation, or process areas with an automatic extinguishing system. The system shall automatically initiate an occupant evacuation alarm signal (NFPA 101 28-3.2 and 28-3.4.3.2). 3.15.2.3 Design Criteria. Where fire alarm systems are required, alarm and detection devices shall be provided as shown in Table 3-3. For the basic functions of protective signaling and control systems including fire detection, alarm, and communication, see NFPA 101 Section 7-6. 3.15.2.4 Code References. Other documents from NFPA, as well as other sources, provide specific information on fire alarm system requirements, installation, sources of hazards, and sources of ignition. The following documents contain additional information: x NFPA 45, Laboratories Using Chemicals; x NFPA 49, Hazardous Chemicals Data; x NFPA 70, National Electrical Code; x NFPA 72A-E, Standards for Fire Alarm System Installation; x NFPA 101, Life Safety Code; x NFPA 491M, Chemical Reactions; x NFPA 497A, Classification of Class 1 Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas;

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MWD Electrical Design Manual 1

Table 3-3. Requirements for Fire Alarm and Detection Devices Area

Initiation

Industrial occupancy

Notification

Manual or automatic

Audible alarm in continuously attended location for initiating action

Business occupancy

Underground structure

Manual or automatic detection

General audible alarm or live public address from

or sprinkler

alarm at continuously attended location

Manual or automatic


Windowless structure

Manual or automatic


Laboratory

(not specified)

All persons endangered and local fire department to be alerted

High hazard area

Automatic extinguishing system General audible alarm

1

In addition to an audible alarm, a visual alarm may be required by the governing authorities in some cities and

counties.

x NFPA 820, Fire Protection in Wastewater Treatment Plants; x Chlorine Institute, Properties of Chlorine. 3.16

ELECTRICAL TESTING

3.16.1 General Requirements The electrical testing and equipment checkout process cannot be designed into a project. Thus, it is necessary that the required testing and checkout procedures be established in the project specifications. Electrical testing of the power system and its associated equipment is an absolute requirement that will provide a safe and reliable electrical system, as well as prevent damage to equipment and possible injury to operating personnel. The testing and checkout process must be started during the period the equipment is being manufactured, and should be continued by the electrical contractor during, and upon completion of, the plant construction. It is the designer's responsibility to be familiar with the testing and checkout procedures in order to be able to specify what is required of the contractor. In general, the electrical testing and system checkout should include the following: x The power supply as furnished by the serving electric utility company;

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STANDARD ELECTRICAL DESIGN PROCEDURES x Manufactured electrical equipment;


x Electrical distribution and branch circuit wiring; x Electrical connections and terminations; x Grounding; x Lighting levels and controls. 3.16.2

Plant Electrical System

3.16.2.1 Utility Service Tests. The utility company's incoming threephase service voltages should be continuously recorded for a period of 24 hours at the point of termination after the installation is essentially complete and the plant is in operation. Voltage amplitude and balance between phases for loaded and unloaded conditions should be recorded and reviewed. If an unbalance, as defined by NEMA, exceeds 1 percent, the cause of the unbalance should be located and corrections should be made. Should the voltage vary by more than plus or minus 4 percent throughout the day from loaded to unloaded conditions, a request should be made to the utility company to have the condition corrected. 3.16.2.2 Equipment Line Current. The line current in each phase conductor for all three-phase equipment and/or for each substation, switchgear, switchboard, and panelboard should be measured and recorded after the utility company has made final adjustments to the incoming service voltage. 3.16.2.3 Equipment Operations. Require the contractors and/or equipment suppliers to check out each item of equipment and demonstrate that it operates in accordance with the requirements of the project specifications. The contractor must demonstrate that protective functions are operating properly and are properly incorporated into the electrical system protection and control schemes and into the plant control system. 3.16.2.4 Plant Illumination. The plant illumination system should be visually checked after the fixture installation has been completed. The initial lighting levels should be checked against the design criteria and for compliance with Title 24 of the State Administrative Code requirements. Exterior lighting should also be checked for proper fixture aiming.

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STANDARD ELECTRICAL DESIGN PROCEDURES 3.16.3


Medium and Low Voltage Equipment

3.16.3.1 Transformers. Liquid-filled and dry-type transformers should receive all standard commercial tests in accordance with ANSI C57.12.90 at the factory. These standard transformer tests include the following: x x x x x x

Applied potential; Induced potential; No load losses; Voltage ratio; Polarity; Continuity.

The manufacturer will also perform the following additional tests on units identical to the design type being supplied: x x x x x

Sound level; Temperature rise; Full-load losses; Regulation; Impedance.

Prior to energizing a transformer, the contractor should perform the following checks: x Perform phase-to-phase and phase-to-ground megohmeter test to verify winding integrity and dryness. x Check for proper installation of vibration dampeners. x Check the adequacy of wall or floor mounting/anchor bolts. x Check and exercise all auxiliary devices such as fans, alarms, and gauges. x Obtain liquid sample from liquid-filled transformers and have analyzed for moisture content, voltage breakdown limits, and amount of contamination. x Visually check liquid-filled transformers for proper oil level and oil leaks at the bushings, valves, gauges, covers, handholes, and radiators. x Insulation power factor test on transformers with windings rated 2.4 kV and above.

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After a transformer has been energized, the contractor should make the following checks and/or tests: x x x x x

Proper voltage level; Load balance between phases; Correct polarity; Phase rotation; Ambient temperature.

3.16.3.2 Switchgear/Switchboards. Switchgear should be conformance tested at the factory in accordance with ANSI C37.51 standards. Switchboards are designed, built, and tested under the requirements of NEMA PB-2 and Underwriters' Laboratories UL-891 standards. Field tests performed by the contractor consist of operational tests of all instrumentation and protective devices and ground fault protection devices. All protective device and instrument circuits should be tested using primary injection. 3.16.3.3 Motor Control Centers. Motor control centers are designed, built, and tested under the requirements of NEMA ICS-2-322 and Underwriters' Laboratories UL-845 standards. Field tests should be performed by the contractor to demonstrate operation of all protective devices and correct operation of all control logic. 3.16.3.4 Automatic Transfer Switches. Automatic transfer switches are designed, built, and tested in accordance with Underwriters' Laboratories 1008 standards. Field inspections and tests should be performed to verify that the phase rotation of the two sources are the same and that all time delays are set in accordance with the requirements of the specifications. 3.16.3.5 Medium and Low Voltage Motors. Motor insulation is generally field and/or shop tested by utilizing a megger-type insulation tester, which is essentially a high-range resistance meter (ohmmeter) with a built-in dc generator. Motor insulation is also tested using a power factor test set. This test measures the ratio of the insulation loss and voltamperes at a specified test voltage. Alternating current is sometimes used for high potential testing; voltage is increased to some specified point to determine whether or not the insulation will fail at that particular voltage. This ac test procedure is a "go, no go" type of test and can cause insulation damage, in contrast to the dc test, which is basically nondestructive. Ac tests are used for proof testing of equipment (that is, to verify that a motor meets prescribed standards), while dc tests provide more qualitative results.

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Conductors

3.16.4.1 Medium Voltage Conductors. The method of testing medium voltage conductors in the field involves the application of a high potential direct-current (DC) source to a series-connected cable assembly. This field test should only be utilized to assure freedom from electrical weakness in the circuit caused by such things as mechanical damage, poor workmanship when making splices and/or terminators, unexpected environmental factors, etc. This field test should not be used to create a complete failure in the dielectric or shielding systems, nor should the dc potential be excessive such that it would initiate punctures in otherwise good insulation. 3.16.4.2 Low Voltage Conductors. Low voltage conductors are tested by the use of a megger insulation tester, which is essentially a high-range resistance meter (ohmmeter) with a built-in dc generator. This test method is nondestructive; that is, it does not cause deterioration of the insulation. This field test can be performed with the conductors either connected to or disconnected from the equipment being served by the circuit. 3.16.5

Emergency/Standby Generators

3.16.5.1 Engine Generators. Engine generators are generally packaged as a single unit. Thus, it is common practice to have a manufacturer performance test the engine generator set in accordance with MIL-STD-705 and IEEE Standard 115. In addition to these standard test requirements, the manufacturer should factory test the engine generator unit a minimum of 3 hours with 2-hour continuous operation at 100 percent rated load having a 0.8 power factor, and 1-hour continuous operation at 110 percent rated load. After the engine generator has been installed, the contractor should perform an onsite test at full load using resistive load banks for a minimum of 4 hours. Results of this test should be compared with the test performed by the manufacturer and the requirements of the specifications. 3.16.5.2 Switchgear/Transfer Switches. Switchgear and transfer switches, having been factory tested, should then be tested after the engine generator has been installed, tested, and connected to the plant distribution system. Power failure should be simulated to verify that the emergency power system will function as intended. The various alarms and shutdown devices should also be checked during this operational test.

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Grounding

3.16.6.1 Ground Rods/Grid. The ohmic value of a single ground rod is usually obtained by the use of a direct-reading earth tester. The testing of a grounding grid system is accomplished by using a null-balance earth tester. Each of these testers has a voltage source, an ohmmeter to measure resistance directly, and switches to change the instrument's resistance range. The basic test method used to determine earth resistance is the direct method (known as the Two-Terminal Test) and the fall-of-potential method (known as the Three-Terminal Test). The direct method is the simplest way to make an earth-resistance test because only two electrodes in series are measured; however, this method is not as accurate at the fallof-potential method, which requires three electrodes. 3.16.6.2 Equipment Ground Busses. Equipment ground busses and the ground wire connection to the equipment bus is generally tested by the direct method of testing. 3.16.6.3 Ground Fault Devices. Ground fault devices such as ground fault interrupter receptacles should be tested for operation with methods and instruments prescribed by the manufacturer. Generally, all that is required to test these devices is a push of a button. Circuit breakers that include ground fault protection devices should be tested by the current injection method.

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Chapter 4

CONTROL SYSTEM DESIGN PROCEDURES


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4.1 CONTROL PANELS Control panels shall concentrate local process control and monitoring functions from within a given area. Control panels shall provide manual control of process equipment. Control panels shall be designed to permit interfacing with the field equipment and the remote terminal units. Control panels shall provide the means for the operator to take over control from remote terminal units (RTU). The panels shall only be used in case of RTU unavailability. The panel design shall consolidate functions wherever possible. This section contains design standards for panel layouts, construction, and some representative control and monitoring devices mounted on or in the panels. 4.1.1 NEMA Standards Panel types shall be compatible with and suitable for the environment of their installed location, and shall protect instruments and equipment enclosed. The choice of location for panels shall minimize exposure to ambient temperature extremes, moisture, dirt, and gaseous contaminants. Panels shall be designed, manufactured, and tested in accordance with the latest applicable standards of NEMA, IEEE, and ANSI. See Appendix D for the complete list of NEMA enclosure types that shall be used to select an enclosure. 4.1.2 Panel Design Panels and cabinets shall be designed to accommodate all necessary accessories such as instrument air, power supplies, mounting hardware, terminal blocks, and signal conditioning or conversion equipment required. Panel layout and equipment spacing shall allow for device removal, calibration, and maintenance without disassembly or adjacent devices. Removable eye bolts shall be provided for sling handling of enclosures. Eye bolt mounting shall be a part of the structural support bracing to distribute stresses and enclosure weight. Sufficient structural reinforcements shall be provided to ensure a plane surface, to limit vibration, and to provide rigidity during shipment,

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MWD Electrical Design Manual CONTROL SYSTEM DESIGN PROCEDURES installation, and operation without distortion or damage to the panel or injury to any mounted instruments. Enclosure seams shall be continuously welded and ground smooth to be undetectable after painting.

Enclosures shall be designed for wall-mounting or be free-standing, as appropriate. For enclosure installation seismic requirements, refer to ESD-103, Structural Design Manual. Free-standing enclosures for areas accessible through manholes shall have maximum dimensions of 72 inches high by 24 inches wide by 24 inches deep to allow passage through 36-inch round manholes. 4.1.3 Indicating Devices Indicators include rectangular panel meters, edgewise panel indicators, digital readouts, and graphic displays. Instruments or devices shall be suitable for panel mounting. 4.1.4 Switches, Pushbuttons, and Lights Refer to Metropolitan's Standard Specifications for detailed specifications of switches, pushbuttons, and lights. Selector switches, pushbuttons, and indicating lights shall be supplied by one manufacturer to assure similar appearance. Selector switches and pushbuttons shall be supplied with operator mechanisms, appropriate number of contact blocks, legend plate, and necessary inserts. Contact block terminals shall be labeled for identification and contain not less than one single pole, double throw contact. Indicating lights shall be LED type. Indicating lights shall have bulb removal and bulb replacement possible from the front of the panel. A push-to-test feature shall be provided for lamp testing. Panel indication lamps--the color of indicator lights shall denote the lamp functions as follows: x Status and alarm lights: Color

Function

AmberOverload Red Equipment running, valve fully open, circuit breaker closed, or high speed Green Equipment stopped (safe), valve closed, circuit breaker open, or low speed White Valve intermediate position or alarm and

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CONTROL SYSTEM DESIGN PROCEDURES automatic or manual


4.1.5 Annunciators Indication of alarms shall be displayed on a panel-mounted, internally illuminated, solid-state annunciator. Annunciator power rating shall be 120 volts ac, 60 Hz. Lamps shall have a nominal 20,000 hours minimum life at rated voltage. All positions in the annunciator cabinet shall contain one solid state alarm plug-in module. Each annunciator alarm point shall have one alarm module. The alarm module shall be capable of accepting a normally open field contacts that close on alarm or normally closed contacts that open on alarm, selectable by a slide switch. The annunciator sequence shown in Table 4-1 is an example of the many sequences available. For other annunciator sequences refer to ANSI/ISA-518.1. The annunciator cabinet shall be suitable for front-panel mounting. Terminals for field connections shall be accessible from the rear. The design of the unit shall permit front-of-panel relamping. Annunciators shall provide auxiliary signals for remote annunciation of each and every point. The annunciator shall be provided with horn and pushbuttons for reset, silence (acknowledge), and lamp test functions. Annunciator pushbutton colors shall be: Color

Function

Green Blue Yellow

Reset Test Acknowledge

Specific alarm functions shall be described in English block-type letters and front engraved on a white, translucent material, 3-inch-by-7/8-inch display window with characters 5/32-inch high. Engraved characters shall be filled with black heat-resistant epoxy resin.

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Table 4-1. Annunciator Sequences Condition

Visual Annunciator

Audible Annunciator

Off

Off

Intermittent Fast flash Fast flash

On

Operator Acknowledgement 1st alarm 2nd alarm

Slow flash Steady on

Off Off

Operator Reset 1st alarm 2nd alarm

Steady on Steady on

Off Off

Off

Off

Normal Off Normal 1st alarm 2nd alarm steady

Return to Normal

On

4.1.6 Relays and Timers Control logic relays shall be heavy-duty, machine tool industrial-type with contacts rated not less than 10 amperes at 600 volts ac. Relay coils shall be molded construction and operate on 120 volts ac 60 Hz, ±10 percent. Auxiliary interposing relays shall be supplied by the same manufacturer to assure similar appearance and uniform operating characteristics. Relays shall have a clear polycarbonate dust cover. Relays shall be UL recognized. Operating temperature range shall be compatible with the environment in which the relay will be installed. Contact material shall be gold or gold flashing over silver and rated 0.5 amperes at 125 volts ac in instances where low-level signal currents are being switched. Relay shall be an octal or 11-pin base plug-in type furnished with appropriate sockets. Electrical timing relays shall be supplied by the same manufacturer to assure similar appearance and time setting procedures. Operating voltage shall be 120 volts ac 60 Hz ±1 percent. Contact rating shall be 10 amperes at 120 volts ac and have a minimum mechanical life of 1 million operations. Operating temperature range shall be compatible with the environment in which the timer will be installed.

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On-delay and/or off-delay shall be supplied as required. Repeat accuracy shall be ±5 percent or better. Reset and recycle time shall be 200 milliseconds maximum. Time delays shall be adjustable with a graduated knob on the timer body. 4.1.7 Control Panel Layout The primary function of a panel and the I&C items on it is to provide the best possible communication between the operator and the process. To establish this communication, the operator has to (1) be able to clearly see the information the instrumentation is providing, and (2) be able to react quickly and accurately to that information. For the operator to see the information clearly on the instruments, lighting is important. Also, the information has to be within the range of vision; therefore, the position of the instrumentation is also important. Thirdly, for the operator to react quickly and accurately, the controls have to be within easy reach. Therefore, the position of the controls is important. Not only must the operator be able to reach the controls, they must also be placed in a logical manner so that the hands will tend to reach for the correct control automatically with the least chance of error. All panels for a given facility shall be designed with the same format so that the operator need not relearn panel configuration concepts while moving around the plant. The following guidelines shall be followed in designing front panel layouts for consistent and efficient operator interface. x Front panel components shall be grouped functionally. The grouping of components shall be clearly distinguished by extra spacing between groups and by the use of group nameplates. The group nameplates shall be larger or longer than individual component nameplates. x Functional groupings shall be arranged from left to right corresponding to process flow or equipment number. For example, controls for Pump No. 1 would be on the left and controls for Pump No. 2 would be on the right. x Panel components shall be located in the following general areas of the panel: Annunciators and alarms, uppermost panel area Graphic panels, uppermost panel area

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MWD CONTROL SYSTEM DESIGN PROCEDURES Indicators, 36 to 60 inches from the floor

Electrical Design Manual

Recorders, 36 to 60 inches from the floor Hand switches and lights, lowest panel area but no lower than 30 inches from the floor x Status indicating lights shall be located directly above their corresponding control switches. 4.1.8 Wiring and Terminations Refer to Metropolitan's Standard Specifications for detailed specifications on wiring and terminations within a control panel. Internal panel wiring and terminations shall be in accordance with the National Electrical Code. Low-level signal wiring shall be segregated from control power wiring, grouped functionally, and arranged neatly to facilitate circuit tracing. No combination of analog, digital input, or control output wiring shall be within the same bundle or duct or panduit within a panel. Signal wiring shall be uniformly twisted. Plastic wiring wraps shall be used to bundle wires, except within wiring ducts. The bundles shall be securely fastened to the steel structure at intervals not exceeding 12 inches. Solderless ring lug connectors with insulating sleeves shall be used for connecting wires to terminal blocks. Flexible stranded wiring shall be used throughout. Where shielding is required, shields shall be continuous foil or metalized plastic providing 100 percent coverage. A drain wire in continuous contact with the shield shall be included. The dc signal wiring shall be segregated from wire conducting ac signals. Power wiring insulation shall be rated to 600 volts and be type MTW. Conductors shall be stranded copper. No wire smaller than 12 AWG 90o C shall be used for power wiring. Wiring must not be spliced. Wire must be run in continuous lengths from screw terminal to screw terminal. Wire service loops shall be provided to permit device removal and to permit front door of control cabinet, if equipped and wired with door-mounted devices, to open 90 degrees.

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Terminal blocks shall be provided for interconnections with field instruments and termination cabinet wiring. Design of the terminal layout shall include a grounded barrier to segregate those terminals devoted to current type signals. The terminal blocks shall be factory assembled on a mounting channel and the channel bolted to the inside of the panel. Terminals shall accept wire size 12 AWG and smaller. Terminal blocks shall be rated 300 volts for NEMA general industrial control devices and 600 volts NEMA for power circuits. No miniature terminal blocks shall be permitted. The terminals shall have a continuous marking strip. Separate terminals shall be provided for terminating the shield wire for each signal. The terminal blocks shall have point identification strips. Terminal strips shall be labeled horizontally from left to right (facing enclosure front) 1F, 2F, 3F, 4F, etc., and facing rear of enclosure 1R, 2R, 3R, 4R, etc. Vertically the terminations shall be marked with a permanent, continuous marking strip from top to bottom. One side of each terminal strip shall be reserved for field incoming conductors. Common connections and jumpers required for internal wiring shall not be made on the field side of the terminal. No more than two wires shall be terminated at any one terminal. A minimum of 25 percent spare terminals shall be provided. Two 1/4-by-1-inch copper ground buses with M5 and M6 tapped holes and insulated mounting brackets shall be provided in each cabinet or panel, one for shield and cabinet grounding and one for signal grounding. Wiring shall be identified at each termination by marking with a number to correspond with the wiring diagram and shall be color coded as follows: x Line and load circuits, ac or dc power: black; x ac control circuits: red; x dc control circuits: blue; x Interlock control circuits on the panel energized from external source: yellow; x Equipment grounding conductors: green; x Current carrying grounded conductor (neutral): white.

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MWD Electrical Design Manual CONTROL SYSTEM DESIGN PROCEDURES External wiring shall be color coded as shown in paragraph 4.2, Field Wiring.

Wires and cable terminated within control panels, instrumentation panels, and termination cabinets shall be provided with identification tags as shown in paragraph 4.2, Field Wiring. 4.1.9 Nameplates Nameplates shall be installed on the doors or covers of panels, panelboards, starters, contactors relays, and other electrical equipment. Equipment within panels shall be identified. Front panel nameplates for devices shall be black laminated plastic with white letters, attached with No. 2-56 stainless steel machine screws, Phillips type, counter sunk head. 4.1.10 Installation Before any circuits are energized, internal and external electrical and mechanical clearances must be checked to assure that installed equipment will function safely and properly. Free standing panels shall be shimmed level and grouted. Panels shall bear evenly over the full length and be installed plumb. Panel structures must be accurately leveled such that panel structures will not be distorted and all doors must operate without binding. 4.1.11 Seismic Design Requirements Equipment base and anchorage shall be designed and installed to withstand stresses caused by seismic forces. Refer to Metropolitan's Structural Design Manual. Panels, consoles, and cabinets mounted on concrete floor shall be bolted through a structural member to the floor at four corners. Equipment located on a raised floor in the control and computer rooms shall be secured to the concrete floor with tie-down cables at four corners. The cables shall be angled to prevent tipping.

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CONTROL SYSTEM DESIGN PROCEDURES 4.2

FIELD WIRING

4.2.1

Field Signal Wiring


4.2.1.1 General. Field signal wiring includes monitoring and control signal wiring between field equipment (sensors, valves, and motor control centers), control panels and remote terminal units (RTU). 4.2.1.2 Sizing. Single pair wires shall be 18 AWG or larger. Multipair conductors shall be 22 AWG or larger. Thermocouple extension wires shall be solid conductors of the same material as the associated thermocouple. 4.2.1.3 Insulation. Signal wiring insulation shall have a minimum dielectric strength of 600 volts. Insulation temperature range shall extend to at least 75o C in dry locations and 90o C in wet locations. Multipair cable overall jacket material shall be moisture-resistant, abrasionresistant, flame-retardant, and compatible with the environment in which it is installed and shall be type TC tray cable. 4.2.1.4 Color Code Identification. Each wire shall have a color code identification to facilitate wiring and troubleshooting. The colors of individual conductors shall be in accordance with NEMA WC-70 as follows:

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1-Black

7-Red/Black

13-Blue/Red

2-Red

8-Blue/Black

14-Orange/Red

3-Blue

9-Orange/Black

15-Yellow/Red

4-Orange

10-Yellow/Black

16-Brown/Red

5-Yellow

11-Brown/Black

17-Black/Blue

6-Brown

12-Black/Red

18-Red/Blue 19-Orange/Blue

The following abbreviations shall be used for identification of multiconductor cables and colored wires when developing wire lists or documentation:

Color

Abbreviation

Color

Abbreviation

Black

B

Brown

BR

White

W

Red

R

Green

G

Orange

O

Gray

GY

Blue

BL

Yellow

Y

4.2.1.5 Twisting. Signal wires shall be uniformly twisted with a minimum of six twists per foot (2-inch lay). Cable lays and pairs shall be twisted in the same direction. 4.2.1.6 Shielding. Where shielding is required, shields shall be continuous foil or conductive metalized plastic providing 100 percent coverage. A drain wire in continuous contact with the shield shall be included. 4.2.1.7

ESD-106

Signal Wire and Cable Selection. Type

Description

I II

Single, unshielded, twisted pair Single, shielded, twisted pair

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CONTROL SYSTEM DESIGN PROCEDURES III IV


Multipair, overall shielded cable of Type I wire Multipair, overall shielded cable of Type II wire

x Analog Signals Analog signals are isolated 4-20 mA inputs received from remote instruments and isolated 4-20 mA outputs transmitted to remote control elements. Type II and IV wiring shall be used for individual and multipair runs, respectively. x Contact Inputs Contact inputs originating from isolated contact closures and conducting less than 10 mA at 48 volts dc. Type I and III wiring shall be used for individual and multipair runs, respectively. 4.2.1.8 Instrument Power and Control Wiring. Wire and cable insulation shall be 600-volt type THHN or THWN. Conductors shall be stranded copper. As a general rule, no wire smaller than No. 12 AWG shall be used for power wiring. Contact outputs are isolated contacts from interposing relays actuated by the RTU for controlling 120-volt devices. No wire smaller than No. 14 AWG shall be used for control wiring. 4.2.1.9 Shield Grounding. Signal shields shall have one ground point located at the source of the signal (e.g., analog transmitter or contact closure) unless otherwise recommended by the instrument or equipment manufacturer. Shields shall be continuous through cabinets, panels, and junction boxes. 4.2.1.10 Splicing. A minimum distance of 1,000 feet between splices shall be maintained. Splicing shall only occur at a junction or pull box. Continuity of conductors and shields shall be maintained at each splice. Connections shall be made gas tight by compressing the two wires to be joined with an isolated compression device or bolted connection. Thermocouple, RTDs, and other low-level signal lines shall be continuous

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MWD Electrical Design Manual CONTROL SYSTEM DESIGN PROCEDURES from the thermocouple connection head to the final termination point.

4.2.1.11 Terminations. Wire at both ends of the cable shall be terminated with preinsulated solderless or compression type spade or ring lugs for maximum physical strength and electrical conduction. Use ring lugs for terminations subject to vibration and for all current transformer secondary circuits. Wires shall not be terminated on adjacent terminal points if accidental short circuiting could cause tripping or closing of a breaker. 4.2.1.12 Separation of Signal Wiring. x Analog Signals Signals in one cable or conduit shall be of the same magnitude. The following peak voltage levels define the different signal magnitude: -

0 to 100 mV; 100 mV to 5 V; 5 V to 75 V.

Analog signals shall be physically separated from contact output and power wiring using separate conduit for each. Low-level analog and control or power wiring shall cross at right angles. Parallel runs of analog and control or power wiring shall be avoided, but, where required, shall be separated by at least 3 feet. x Digital Signals Digital input and control wiring, using unshielded pairs, shall be run in separate conduits. If they are run in the same conduit, the pairs must be twisted and shielded. 4.2.1.13 Installation. Wiring inside enclosures shall be supported at least every 24 inches unless longer unsupported runs are required for access or maintenance. Wiring to doors shall be installed such that bending is axial, with no tension exerted on wiring with doors in any position.

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CONTROL SYSTEM DESIGN PROCEDURES 4.2.2


Conduit

4.2.2.1 Construction. Conduit construction must be in accordance with the latest revision of the National Electrical Code. The conduit shall be of galvanized rigid steel with a flexible section for connection to devices. Conduit that has been crushed or deformed in any way shall not be used. 4.2.2.2 Number of Bends. Bends of rigid conduit shall be made such that the conduit will not be injured and that the internal diameter of the conduit will not be effectively reduced. The radius of the curve shall not be less than that recommended by either the National Electrical Code or manufacturer of the wires or cables to be contained within the conduit. The maximum angle of bends between pulls shall not total more than 180 degrees including entrance and exit to pull boxes or access fittings. 4.2.2.3 Distance Between Pull Points. The maximum allowable distance between pull points shall be 300 feet or the distance based on allowable maximum cable pulling tension, whichever is less. When the distance between the two pull points contains the maximum angle of bends, as stated above, the maximum allowable distance shall be 75 feet. A lubricating agent compatible with the wire insulation shall be used. The pull boxes shall be sized to allow adequate bending radius for the wire or cable being pulled. 4.2.2.4 Conduit Fill. The combined cross-sectional area of conductors and cables in a conduit shall not exceed the fill percentages specified by the National Electrical Code. 4.2.2.5 Conduit Support. Conduit shall be firmly supported within 3 feet of each pull box, junction box, or termination point. The conduit shall be sufficiently supported elsewhere in accordance with the National Electrical Code requirements.

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4.2.2.6 Continuity. Conduit runs shall be solidly connected to assure the ground continuity of the entire run. Ground jumpers shall be installed where the possibility of losing continuity exists. 4.2.2.7 Condensation Drains. Conduit runs shall be provided with condensation drains at low points. 4.2.2.8 Installation. Exposed conduit runs shall be parallel or perpendicular to building walls. 4.2.3 Spare Conductors Spare conductors in each conduit equal to 25 percent of the number required for both present and (defined) future conditions, but in no case less than two spare wires, shall be installed. Each cable shall have 10 percent spare conductors but not less than two conductors. 4.3 CONTROL DEVICE INTERFACING This section covers the design requirements for the interface between remote terminal units and field control devices. Included are the types of input and output hardware at the RTU, interlocks and manual control equipment at field control panels, stations and alarm monitoring at the field control devices, and control hardware at the field devices. Control circuit diagrams for various types of field devices are shown on Figures 4-1 through 4-10 (located at the back of this chapter). The following are the types of field devices specifically covered in this section. Design requirements for other field devices shall follow the general requirements established in this section. x Modulating control valves: Electric motor operator; Hydraulic actuator. x Open/close control valves: Electric motor operator; Hydraulic actuator. x Electric motors: Constant speed; Multiple speed; Variable speed.

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Remote Terminal Unit Outputs

4.3.1.1 RTU Termination Cabinet Remote terminal units (RTU) shall have a termination cabinet. The size of the termination cabinet is slelected based on the number of I/O terminations in the RTU. Termination cabinets shall be 36” or 48” or 60” wide, 24” deep and 72” or 76” high for Metropolitan’s small or standard RTU, and 20” wide x 20” high x 8” deep for wall-mounted RTU. Separate terminal blocks shall be provided for analog discrete signals. Analog signals shall have three terminal blocks, one each for signal (+), signal(-) and shield. Each discrete input and output shall have two terminal blocks. The terminal blocks for analog and discrete signals shall be switch type terminal block to permit isolating and testing of the signal loop. Termination cabinets shall be supplied with non-UPS 120V AC power for enclosure lights and outlets, and a copper grounding bar with M5 and M6 tapped holes and insulating mounting brackets. It is Metropolitan’s practice to terminate all conductors between TRU and the corresponding termination cabinet for the construction contractor to terminate field wiring between termination cabinet and field mounted devices. 4.3.1.2 Contact Outputs. Contact outputs to field control devices shall be momentary contact closures using interposing relays, with the duration of the closure controlled by RTU hardware. Two contacts shall be provided for each control device; one to initiate control action, the other to stop or reverse control action. The time between initiating and stopping or reversing control action shall be controlled by RTU software. Seal-in circuits shall be provided in either the field control panel or the motor starter. 4.3.1.3 Modulating Outputs. Modulating devices such as variablespeed pumps and automatic control valves shall be controlled by isolated 4-20 mA outputs. Contact closure-type outputs shall be used for constant speed motor-operated valves and gates. For contact closure-type outputs, two separate contacts are required for each device. Closing one of the contacts shall cause the motor to operate, the other shall cause the motor to reverse. When neither contact is closed, the motor is stopped. The position of the device shall not change during loss of remote control. In addition, transfers between remote and local control are made without changing position.

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Control Panels

4.3.2.1 Control Transfer Switch. Control transfer switches shall be provided at control panels to select either remote (from RTU) or local (at the control panel) control. Auxiliary contacts shall be available for reporting to the RTU. Field devices may be grouped or be individually controlled by one control transfer switch. The control transfer switch shall be maintained in each position. 4.3.2.2 Panel Controls. Pushbutton controls on the control panels shall be momentary to match the RTU outputs. Pushbuttons shall not operate unless the control transfer switch is in the local position. (See Figure 4-1.) Indicating lights, of the colors shown on the figures, shall be provided on the control panel adjacent to pushbuttons to show control device status. Indicating lights may be incorporated into the pushbuttons if desired. 4.3.3

Status Monitoring

4.3.3.1 Valve Monitoring. Limit switches shall be furnished to monitor the fully closed and open position of flow routing valves and gates. Full open-close type valves that are remotely controlled shall have limit switches for both the open and closed positions. Manual valves and gates used solely for maintenance (e.g., pump suction and discharge isolation valves) shall have limit switches as required. Throttling valves shall have limit switches for fully opened and closed position monitoring and a 4-20 mA output signal for monitoring valve position. Limit switches and the position signal shall be furnished by the valve manufacturer as an integral part of the valve assembly. Whenever possible, a 4-20 mA position signal is preferred instead of a potentiometer. 4.3.3.2 Motor Monitoring. Motor starter auxiliary contacts shall be provided for remote monitoring of the running status of motors that are controlled by the RTU. Large motors, generally over 100 horsepower, that are critical to the process, plant, or system shall be monitored for alarm conditions such as high bearing temperature, high motor winding temperature, and motor vibration. Equipment and personnel safety interlocks shall be locally hardwired to

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MWD Electrical Design Manual CONTROL SYSTEM DESIGN PROCEDURES the control panels to function independently of the RTU. Examples of interlocks are a low-level switch contact used to prevent pumps from running dry and a valve limit switch used to prevent a pump from being started against a closed valve.

Motors controlled by the RTU shall be equipped with a pushbutton switch control or other type of disconnect in accordance with the National Electrical Code, which is capable of interrupting power to the motor starter pilot circuit. 4.3.4 Signal Convertors Signal converters shall be provided as needed to condition analog signals for input to the computer system RTUs and control panel devices.

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Appendix A

REFERENCES


Note: The most current edition of referenced publications applies, unless otherwise specified. American National Standards Institute ANSI C2, National Electrical Safety Code California Code of Regulations CCR Title 8, Division 1, Chapter 4, Subchapter 5, Electrical Safety Orders CCR Title 24. California Building Standards Code Institute of Electrical and Electronics Engineers Note: Many IEEE documents are adopted by ANSI and have an ANSI/IEEE document number similar to the IEEE document number. IEEE Std 80, IEEE Guide for Safety in AC Substation Grounding IEEE Std 141, IEEE Recommended Practice for Electric Power Distribution for Industrial Plants IEEE Std 142, IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems IEEE Std. 242, IEEE Recommended Practice for Protection and Coordination of Industrial and commercial power systems IEEE Std 399, IEEE Recommended Practice for Industrial and Commercial Power Systems Analysis IEEE Std 422, IEEE Guide for the Design and Installation of Cable Systems in Power Generating Stations IEEE Std 433, IEEE Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems IEEE Std 446, IEEE Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications IEEE Std 484, IEEE Recommended Practice for Installation Design and Installation of Large Lead Storage Batteries for Generating Stations and Substations IEEE Std 493, IEEE Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems IEEE Std 519, Recommended Practice and Requirements for Harmonic Control in Electrical Power Systems

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Appendix A

REFERENCES


IEEE Std 525, IEEE Guide for the Design and Installation of Cable Systetms in Substations IEEE Std 605, IEEE Guide for Design of Substation Rigid-Bus Structures IEEE Std 739, IEEE Recommended Practice for Energy Management in Industrial and Commercial Facilities IEEE Std 979, IEEE Guide for Substation Fire Protection IEEE Std 980, IEEE Guide for Containment and Control of Oil Spills in Substations IEEE Std 1050, IEEE Guide for Instrumentation and Control Equipment Grounding in Generating Stations IEEE Std 1100, IEEE Recommended Practice for Powering and Grounding Electronic Equipment IEEE Std 1187, IEEE Recommended Practice for Installation Design and Installation of Valve Regulated Lead-Acid Storage Batteries for Stationary Applications IEEE Std C37.2, IEEE Standard Electrical Power System Device Function Numbers IEEE Std C37.20-1, IEEE Standard for Metal-Enclosed Low-Voltage Power CircuitBreaker Switchgear IEEE Std C37.20-2, IEEE Standard for Metal-Clad and Station-Type Cubicle Switchgear IEEE Std C37.20-3, IEEE Standard for Metal-Enclosed Interrupter Switchgear IEEE Std C37.96, IEEE Guide for AC Motor Protection IEEE Std C37.100, IEEE Standard Definitions for Power Switchgear IEEE Std C37.101, IEEE Guide for Generator Ground Protection IEEE Std C37.102, IEEE Guide for AC Generator Protection Illuminating Engineering Society IES Lighting Handbook National Electrical Manufacturers Association NEMA MG 1, Motors and Generators NEMA 250, Enclosures for Electrical Equipment (1000 Volts Maximum) NEMA WC 70/ICEA S-95-658, Nonshielded Power Cables Rated 2000 Volts or less for the Distribution of Electrical Energy NEMA WC 71/ICEA S-96-659, Standard for Nonshielded Cables Rated 2001-5000 Volts for Use in the Distribution of Electric Energy

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Appendix A

REFERENCES


NEMA WC 74/ICEA S-93-639, 5-46 kV Shielded Power Cable for Use in the Transmission and Distribution of Electric Energy. National Fire Protection Association NFPA 45, Fire Protection for Laboratories Using Chemicals NFPA 70, National Electrical Code (2005 Edition) NFPA 70E, Standard for Electrical Safety in the Workplace NFPA 72, National Fire Alarm Code NFPA 75, Protection of Information Technology Equipment NFPA 76, Fire Protection of Telecommunications Facilities NFPA 79, Electrical Standard for Industrial Machinery NFPA 101, Life Safety Code NFPA 110, Emergency and Standby Power Systems NFPA 780, Installation of Lightning Protection Systems NFPA 820, Protection in Wastewater Treatment and Collection Facilities NFPA 851, Fire Protection for Hydroelectric Generating Plants Underwriters’ Laboratory UL 845, Motor Control Centers UL 891, Switchboards UL 1008, Transfer Switch Equipment Miscellaneous Documents Electrical Installations in Hazardous Locations, Peter J. Schram and Mark W. Earley, editors, National Fire Protection Association Electric Service Requirements, City of Los Angeles Department of Water and Power Electrical Service Requirements Manual, Southern California Edison Electrical Engineer’s Portable Handbook, Bob Hickey, editor, McGraw-Hill Electrical Systems Analysis and Design for Industrial Plants, Irwin Lazar, editor, McGraw Hill Handbook of Electric Power Calculations, H. Wayne Beaty, editor, McGraw-Hill Industrial Power Systems Handbook, Donald Beeman, editor, McGraw-Hill

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Appendix A

REFERENCES


Motor Application & Maintenance Handbook, Robert W. Smeaton, editor, McGraw-Hill Standard Handbook for Electrical Engineers, Donald G. Fink and H. Wayne Beaty, editors, McGraw-Hill Switchgear and Control Handbook, Robert W. Smeaton and William H. Ubert, editors, McGraw-Hill

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Appendix B

ABBREVIATIONS


A A or AMP A/C AC AF AFF AFG AG ASD AT ATS AUX AWG

Ampere Air Conditioner (Conditioning) Alternating Current Ampere Frame Above Finished Floor Above Finished Grave Above Ground Adjustable Speed Drive Ampere Trip Automatic Transfer Switch Auxiliary American Wire Gauge

B BAT BC BET BOT BLDG BKR BTU BTU/H

Battery Bare Copper Between Bottom Building Breaker British Thermal Unit British Thermal Unit Per Hour

C C CAB CAT CB CHLOR CONC CKT CMIL CNTL or CONT CONT’D

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Conduit Cabinet Catalog Circuit Breaker Chlorine Concrete Circuit Circular Mil Control Continued

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Appendix B

ABBREVIATIONS


D D DC DIA or DN DISC DIST DPDT

Depth Direct Current Diameter Down Disconnect Distribution Double Pole Double Throw

E EL or ELEV EXIST EM EPR

Elevation Existing Emergency Ethylene Propylene Rubber

F F FDR FL FLEX FS FVR FVNR

Frequency Feeder Floor Flexible Flow Switch Full Voltage Reversing Full Voltage Non-Reversing

G G GFI GFCI GND or GRD

Ground Ground Fault Interrupter Ground Fault Circuit Interrupter Ground

H H or HGT HDAF HH HOA HP

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Appendix B

ABBREVIATIONS HPF HPU HTR HV HZ


High Power Factor Hydraulic Power Unit Heater High Voltage Hertz

I IEEE INST INSTR I/O ITC

Institute of Electrical and Electronics Engineers Instantaneous Instrument Input/Output Instrument Terminal Cabinet

J J JB

Junction Junction Box

K K KAIC KCMIL KW KV KVA KVAR

Kilo (1000 times) Kiloamp Interrupting Current Thousand Circular Mils Kilowatt Kilovolt Kilovolt Ampere Kilovolt Ampere Reactive

L LP LS LT LTG LV

Lighting Panel Level or Limit Switch Liquidtight Lighting Low Voltage

M M

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Appendix B

ABBREVIATIONS mA MAX MCC MCP MFE MFR MIN MH MOD MV MVA MWD


Milliamp Maximum Motor Control Center Motor Circuit Protector Metropolitan Furnished Equipment Manufacturer Minimum Manhole Module Medium Voltage Megavoltampere Metropolitan Water District

N NC NEC NEMA NFPA NIC NO NO. or # NTS

Normally Closed National Electric Code National Electrical Manufacturers Association National Fire Protection Association Not In Contract Normally Open Number Not To Scale

O

P P PB PDR PF PH or PLC PNL PS PVC PWR

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Pole Pullbox or Pushbutton Preliminary Design Report Power Factor Phase Programmable Logic Controller Panel Pressure Switch Polyvinyl Chloride Power

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Appendix B

ABBREVIATIONS


Q

R R RECPT or RCPT RGS RTU

Resistor Receptacle Rigid Galvanized Steel Remote Terminal Unit

S SCE SHLD SHT or SH SN SP SPDT STD STR SV SW SWGR

Southern California Edison Shield Sheet Solid Neutral Spare Single Pole Double Throw Standard Starter Solenoid Valve Switch Switchgear

T TB TC TD TEL TERM THRU TM TS TSP TST TYP

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Terminal Box Terminal Cabinet Timer Delay Telephone Terminal Through Thermal Magnetic Temperature or Time Switch Twisted Shield Pair Twisted Shield Triad Typical

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Appendix B

ABBREVIATIONS


U UG or U/G UPS UL USA

Underground Uninterruptible Power System Underwriters Laboratories Underground Service Alert

V V VA VFD

Volt Voltampere Variable Frequency Drive

W W W/ WP

Watt With Weatherproof

X XDCR XFMR

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Transducer Transformer

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Appendix C

SAMPLE ELECTRICAL DESIGN CRITERIA MEMO


The (title of facility) is a new facility. This document is intended to provide guidance for the electrical system design. If there is a better way to meet the design objectives, submit a recommendation to the project lead electrical engineer for processing. See the preliminary design report (PDR) for a description of the electrical system to be provided for this project. OBJECTIVES The design objectives on this particular project are clarity, simplicity, and standardization. In addition, the usual standards of the profession will apply such as constructibility, completeness, and reasonable accuracy. Clarity The design and presentation must be clear. Show how you arrived at significant decisions. If you want a specific result, show the contractor what shall be done for the particular situation. Simplicity The design itself, of course, shall not be more complex than necessary to produce a good electrical system. In addition, the presentation shall be as simple as clarity permits. Simplicity shall not go so far as to shift tasks normally accomplished during design into the construction phase. Standardization The design must show uniformity throughout so that similar problems are solved in similar ways. If several people work on areas that can share solutions, they shall only produce one solution and reference it elsewhere. Where possible, manufacturers' standard assemblies shall be used. SCHEDULING An electrical work plan will be provided separately. This section tells what information must be available before beginning the design for each part. The object of having this information available before the design begins is to minimize changes in the electrical design. If the information listed below is not available at the time the design for a particular portion is scheduled to begin, do not begin that portion of the design. Problems that you encounter in obtaining the necessary information will either be immediately resolved or referred to the Design Manager and/or Project Manager.

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Appendix C



Single-Line Diagram A single-line diagram for the plant electrical distribution system is included in the PDR. I will modify this single line as necessary to accommodate changes that have been made since the PDR was completed. Single-line diagrams for motor control centers (MCC) will not be started until a reasonably complete motor list has been developed for the area where the MCC is to be located. The P&IDs shall be used to check the equipment lists given to us by the process leads. Each motor and equipment number shall be checked against the current P&ID set before the equipment list is considered complete. Facility and Process Plans The process electrical design for any area will be started only after the following things have been accomplished for that area: x Equipment data sheets are complete and reviewed by the lead engineer in charge of the process; x Equipment selection calculations have been reviewed; x P&IDs completed. Facility electrical design, lights, and outlets, for any area will be started only after the process design is completed and building plans and sections are prepared and drafted by the architects (changes in process design may still take place). REFERENCE MATERIALS Besides the usual codes and standards, the following documents are available as information. x The PDR and single-line diagrams STANDARDS AND CODES Electrical design shall conform to the latest editions of the following applicable standards and codes: x National Electrical Code (NEC); x National Electrical Safety Code (NESC); x California State Electrical Code; x State of California Code, Title 8, CAL/OSHA Standards Board,

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Appendix C



Subchapter 5, Electrical Safety Orders. Standards and codes of the following organizations shall also govern where applicable: x x x x x x

American National Standards Institute (ANSI); National Electrical Manufacturers Association (NEMA); Institute of Electrical and Electronic Engineers (IEEE); Insulated Cable Engineers Association (ICEA); Occupational Safety and Health Act (OSHA); American Society for Testing and Materials (ASTM).

Local codes and standards shall be applied as appropriate. Where the requirements of more than one code or standard are applicable, the more restrictive shall govern. Requirements of applicable codes and standards are not repeated in this section. Applicable state and local codes and UL listing requirements shall be followed for electrical inspection. Exit signs, emergency egress lighting, and emergency lighting power supply shall conform to requirements of the building inspector. VOLTAGES The primary distribution voltage within the plant shall be 4,160-volt, three-phase. The secondary distribution voltage shall be 480-volt, three-phase, wye, highresistance grounded. Under normal circumstances, the voltage for fluorescent, high pressure sodium, and incandescent lighting shall be 120-volt, single-phase. This voltage also shall be supplied to heaters up to 1,500 watts, convenience outlets, motor controls, and motors of less than 1/2 horsepower (hp). Heaters above 1,500 watts and motors from 1/2 to 200 hp shall be 480 volts, three-phase. Motors above 200 hp shall be 4,160 volts, three-phase. The code allowable total voltage drop from the 480-volt source bus (excluding site distribution) to the point of use (including feeder, branch circuit, and transformation) shall not be exceeded.

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Appendix C



In addition, due to the complexity and expense of providing ground fault protection for three-phase 4-wire double ended substations with multiple grounds, no phase to neutral loads shall be supplied directly from the 480-volt transformer secondaries. DRAWINGS Legend Sheet In general, the standard Metropolitan symbols shall be used. The legend sheet shall contain only the symbols and final abbreviations actually used in the drawing set. The development of this sheet is my responsibility, with input from the project team. A preliminary legend sheet is included in the PDR. Site And Area Plans The site plan shall show the location of all facilities and major equipment, duct bank routes, handholes, and manholes. Area plans shall show all of the above items and facility designs where the facility does not require a separate drawing such as clarifiers, thickeners, etc. Site and area plans shall be overlayed on civil backgrounds (base sheets). Single-Line Diagram The single-line diagram shall show the entire electrical distribution system from the elec trical service down to 460-volt utilization devices and 208Y/120-volt panelboards. Circuiting of 208Y/120-volt panelboards shall be shown on the panel schedules. Circuiting of 480Y/277-volt panelboards shall be shown on the panel schedules where possible, but where motors are powered from panelboards, the branch circuit, including all combination motor starters and disconnect switches, shall be shown on the single-line diagram. Information on single-line diagrams shall include bus capacity, short circuit ratings, overcurrent device types and ratings, C.T. and P.T. ratios, protective relay types and ratings, metering and load ratings (horsepower or kilowatt), and circuit breaker and switch ratings. Conduit and conductor sizes shall be indicated on the single-line as well.

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Appendix C



Elevations Front elevations shall be shown for all medium-voltage switchgear, low-voltage switchboards, unit substations, and motor control centers. Elevations shall be drawn to scale and shall show the locations of MCC units, overcurrent devices, metering, and conductor entrances. MCC units with extra height shall be shown where required for relays. Switchboard and switchgear elevations shall be informally reviewed by the first-named manufacturer for placement of units and overall dimensional accuracy. Where important, note depths of assemblies on elevations. Elevations of the equipment shall be developed by the designer of the facility that the equipment is located in and reviewed by me. Remember that even one control relay in a motor starter will usually require an additional 3 inches of compartment height. Assume that this will be the case when you need to have relays. Two will fit in the added 3 inches; if you need 3, add another 3 inches, etc. Motor Elementary Control Diagrams Motor elementary control diagrams (ECDs) shall be done in the style shown on the attached example. The ECDs shall show control circuit devices, which are not mounted in I&C panels. Single controls in an I&C panel (on/off selector switch, start/stop pushbuttons) may be shown. More complex control in an I&C panel shall be shown as two terminals in a dashed rectangle with a reference to the signals as they are labeled at the I&C panel, such as "RUN M-1-1 @ FP-2." Except as noted below, all control devices shall be shown on the P&IDs. Talk to the I&C engineer before adding control devices. The following control devices, not shown on the P&IDs, shall be shown on the ECDs where we feel that they are necessary: x ON/OFF/REMOTE switch (where required and not shown) x Elapsed time meters (will be provided if the motor falls into the criteria described hereinafter) x Ground fault relays x Metering x Motor heaters x Motor thermal devices x ON/OFF status lights

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Appendix C



ECDs shalll be developed by each facility designer for the equipment located in that facility. Schedules Luminaire and panel schedules shall be put on the drawings. The luminaire schedule shall be prepared in a format similar to the lighting fixture schedule shown on attached example. A preliminary list of luminaires shall be developed before design is started and the same luminaire shall be used for all similar applications throughout the plant. Addition of a new luminaire to the schedule shall require review with the project lead electrical engineer. A preliminary list of luminaires shown in the format to be used is enclosed hereinafter. Panel schedules shall be prepared similar to the panel schedule shown on attached example. The lead design engineer for each facility shall be responsible for the preparation (and review) of all panel schedules related to that facility. A separate panel shall be provided within each facility for the power supply to process related instruments and equipment. In smaller facilities, this panel may be subfed from the lighting panel, but in larger facilities it shall be fed from a transformer and transfer switch that is separated from the building facilities power supply. The panel schedules shall be included on the drawings with the buildings or facilities where they are located or with the single-line diagrams or equipment elevation of the related equipment. The panel schedule format is available upon request. Details Details shall be numbered as noted in the project instructions. The project lead electrical engineer will act as, or appoint a detail coordinator. A preliminary set of design details will be selected and a copy of each will be provided to each design team member. Details will generally be Metropolitan standard details. When you need to use a detail that has already been used, find out the number from the detail coordinator. If it has not been used, obtain a new number from the detail coordinator and tell the coordinator the standard detail number, whether you are modifying the detail or whether you are creating a detail from scratch. Every 1 to 2 weeks, the detail coordinator shall send a copy of details being added to the project to each electrical designer on the project.

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Appendix C



Process And Facility Plans Process and facility plans shall show the location of and connection to all equipment that requires raceway or conductors. A separate connection point shall be shown for each device located within an area, even if they are all supplied as part of the same package, unless the specifications clearly require that all of the devices are to be wired to a single panel or TJB by the supplier of the equipment. Spare raceway for future equipment shall also be shown, where appropriate. If the plans become crowded, the process plans shall be separated from the facility plans. Receptacles, lights, water heaters, HVAC equipment, and other non-process loads shall be shown on the facility plan. See the preliminary drawing list for the buildings and facilities where separate plans are expected. At each connection, show the connected load in kW (where it is 0.5 kW or greater), raceway size, fill, and routing, unless the raceway has an assigned number, in which case just show the raceway and circuit number. Fill shall be called out by number and size of conductors or by circuit name where the circuit appears on the circuit schedule. A list of circuit types with single letter designators shall be prepared for circuit types that will be used repeatedly.They shall be used on all plan sheets where such information will not cause confusion. Routing shall consist of showing the actual routing in cases where this is important or, more usually, showing a homerun and destination. If everything in the conduit is going to the same final destination with no intermediate junctions, just give the destination; e.g., "MCC5A." If, everything in the conduit is going to the same final destination, but has intermediate junctions, give the final destination and the next junction; e.g., "MCC5A via JB-3." If there are several final destinations for the circuits in a conduit, make the destination the next junction point and give the final destinations in the size and fill callout; e.g., "3/4" C, 3#12 to MCC5A, 6#14 to FP-3, 3#4 to MCC5A, 1#12G." Process and facility plans shall be developed by the designer responsible for that facility. DIVISION 11 SPECIFICATIONS Division 11 specifications for equipment that requires electrical connections shall be reviewed for electrical requirements by the electrical design engineer responsible for the area where the equipment will be installed. In addition, the project lead electrical engineer shall review each equipment specification before it is returned to the Design Manager for processing. A list of Division 11 specifications will be prepared that identifies which electrical design engineer is to review which sections.

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Appendix C



DIVISION 16 SPECIFICATIONS Refer to Metropolitan's ESD-135, Standard Specifications Sections Catalog for a list of specifications necessary for this job. These specifications shall be developed by the project lead electrical engineer with input from each electrical design engineer where a specification affects an area they are designing. When developed, these specifications shall be compatible in requirements to Metropolitan Standard Specifications Sections Catalog. CIRCUIT AND RACEWAY SCHEDULES A computer-developed circuit and raceway schedule shall be used for all circuits that are routed through the duct bank system, with the exception of those shown on the area plans (1"=20' scale site plans) where the ultimate destination of the circuit is also shown on the same plan. To coordinate the efforts of all staff having input to the schedules, each electrical designengineer shall be responsible for all circuits that leave their facility and enter the duct bank system. They shall verify that each of their circuits is completely routed through the duct system to its final destination. For cable and circuit identification, refer to AppendixG. Information to be presented in circuit and raceway schedules shall show the following information: x Circuit number; x Circuit end points; x Circuit type (power, control, instrumentation, etc.); x Conductor size, count and type - identify neutral and grounds; x Routing—list raceways in the order that the circuit passes through them. The raceway schedule shall show the following information: x x x x

Raceway number; Raceway end points; Number, size, and type of conduits, e.g., 2-4 inch PVC; Circuits carried in the raceway.

The multiconductor cable schedule shall show the following:

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Appendix C



x Cable number; x Circuits carried in the cable. Each multiconductor cable shall also appear in the circuit schedule. What to include in circuit and raceway schedules. The following circuits and the raceways containing them shall be identified and entered into the circuit and raceway schedule: x Circuits which leave a sheet (exception: circuits which leave one floor plan to a second floor of the same building but do not leave the building). x Circuits which leave a facility, unless they do not leave the sheet, and the routing between facilities is clear. x Circuits which are part of a control cable. An interconnection diagram similar to that shown in Figure 5 shall be prepared for all terminal junction boxes (TJBs) from which a control cable originates. These diagrams may or may not be on the drawings depending on the complexity of the diagram. If a circuit is identified anywhere on its route, it shall be identified for its entire route. All raceways containing that circuit shall also be identified unless the raceway remains entirely within one facility. In such a case, that portion of the circuit may be identified in the circuit schedule and the circuit will be identified as part of the raceway fill on the drawings. Information shall not be duplicated on the drawings and circuit and raceway schedules. For anything appearing in the schedules, just give enough information on the drawings to locate it in the schedules. This means that once the need to identify a circuit has been established, the only information that needs to be put on the drawings about that circuit is the circuit number and the raceways that contain it. FAULT STUDIES A preliminary fault study shall be completed for the entire plant as part of the PDR but no later than the start of final design. The following assumptions shall be made: x An infinite source is available on the high side of each utility service transformer. x The utility service transformers shall not be operated in parallel.

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Appendix C



x The standby engine generators shall not operate in parallel with the utility source but the gas utilization generator shall. x The maximum load operating on each 480-volt bus at each load center shall be equal to 100 percent of the installed transformer capacity at that load center. The study shall show the load and fault duty on each bus and feeder overcurrent device rated 460 volts or higher. The final fault study shall be an update of the preliminary fault study. The final load study shall show the load at each distribution assembly in the following categories: x x x x x

HVAC; Process; Lighting; Other facility loads; Total.

Other categories may be added to the above, if required by the electric utility. PROCESS CONSIDERATIONS Hazardous Areas The project lead electrical engineer shall review the various areas of the plant that may contain hazardous concentrations of hazardous gases. Based on the requirements of NFPA 820, a drawing shall be developed to deal with each area. The areas that will be affected include enclosed areas, scum pits, and similar areas. These are areas open to raw sewage or secondary influent (i.e., up to the aeration basin), which shall be considered Hazardous Class I, Division I due to the presence of methane and gasoline unless adequate ventilation is provided. In addition, the digester gas compressor rooms shall also be classified as Class I, Division I areas. Other areas may be classified hazardous as required by NFPA 820. Devices that contain contacts located in hazardous areas shall generally be wired intrinsically safe, except in Class I, Division II areas where hermetically sealed contacts may be installed.

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Appendix C



Reliability This plant requires EPA Class I reliability. One utility source is available at the plant and a standby generator shall also be provided. The plant shall be designed with double-ended unit substations and MCCs in all facilities. Power for duplicate equipment shall be put into different conduits so as to maintain the Class I reliability. Redundancy of supply criteria shall comply with EPA Bulletin EPA 430-99-74-001 definitions for a Class I plant. UTILIZATION EQUIPMENT CONSIDERATIONS Utilization Equipment Identification Permanent. Utilization equipment shall be identified by I&C tag numbers as those numbers become available. Utilization equipment that does not appear on the P&IDs will be identified in the same manner as electrical distribution equipment (see below) using an appropriate equipment type; for example, UH for unit heater. Interim. Until I&C tag numbers become available, utilization equipment will be identified by the following format: x FF-SS x Where FF is the facility number in or near which the equip ment is located and SS is a sequence number. Sequence numbers shall be assigned in order by the facility designer. Sequence numbers for deleted equipment shall not be reused. Miscellaneous Provide disconnects where required at process equipment, especially at motor-operated valves. Work with the equipment specified to see if integral disconnects are a standard option. Do not ask that they be specified unless they are a standard option. Provide disconnect switches for all HVAC equipment that has any integral controls (i.e., unit heaters, compressors, duct heaters, air handlers, etc.).

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Appendix C



ELECTRICAL EQUIPMENT CONSIDERATIONS Electrical Distribution Equipment Identification A logical and consistent naming and numbering system shall be developed to designate equipment associated with electrical systems. Distribution equipment numbers shall reference the building or facility in which the equipment is located. Several examples of equipment designations based on function and voltage are given below; note that the numeral 5 indicates the equipment is located in Building No. 5. 480 Volts Distribution Panel Switchboard Motor Control Center Emergency Panel

5DP1, 5DP2, 5DP3, etc. 5SB1, 5SB2, 5SB3, etc. 5MCC1, 5MCC2, 5MCC3, etc. 5EP1, 5EP2, 5EP3, etc.

208Y/120 Volts Lighting, Receptacles, and Miscellaneous Power

5LP1, 5LP2, 5LP3, etc.

Emergency Lighting Panel

5EL1, 5EL2, 5EL3, etc.

Equipment-type designations shall be as follows: x x x x

CMS JB MCC MSR

= = = =

x x x x x x x

PNL = DPNL = SB = SWG = TJB = TX = USB =

Combination motor starter; Junction box; Motor control center, medium, or low voltage; Grouped motor control, not part of a manufactured assembly; Panelboard; Distribution panelboards; Switchboard, low voltage; Switchgear, medium voltage; Terminal junction box; Transformer; Unit substation.

Other equipment-type designations may be used. ESD-106

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Appendix C



Sequence numbers are required even if only one of a particular type of equipment is in a particular facility. For TJBs only, the sequence number will be followed by "A" for analog, "D" for discrete, or "P" for power. The following equipment will be identified: x x x x x x x x

Motor control centers; Panelboards; Distribution panelboards; Switchboards; Switchgear; Terminal junction boxes; Transformers; Unit substations;

Other equipment may be identified if identification is required for other purposes; for example, junction boxes may need to be identified in order to homerun to them. Major electrical equipment, i.e., MCCs, SWBDs, etc., shall be located on the site plan and the 1"=20' scale area plans in addition to the facility and process electrical plans. Distribution System Protection The following types of protective devices shall be used for the medium- and low-voltage distribution systems: x 4.16-kV main switchgear assembly: Draw-out vacuum type power circuit breakers in NEMA Type 1 enclosure for indoor or NEMA Type 3R enclosure for outdoor. x 4,160-volt motor control—: Draw-out type vacuum contactors with current limiting fuses in NEMA Type 1 gasketed enclosure. x 480-volt switchboard: 100 percent rated insulated case circuit breaker with solid-state trip for mains and feeders 600 amperes and larger. Smaller feeder breakers shall be molded case with solid state trips. x 480-volt motor control center main circuit breaker: 100 percent rated molded case with solid state trips. x 480-volt motor control center branch circuit breaker (other than combination motor starters): molded case thermal magnetic.

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Appendix C



x 480-volt feeder circuit breaker in motor control centers and power distribution panelboards, 400-ampere and larger: molded case solid-state trip, 100 percent rated. Smaller circuit breakers shall be molded case thermal magnetic. Equipment shall have adequate momentary and interrupting capacity to withstand fault currents that may occur at the point in the system where the equipment shall be applied. Each circuit breaker that is located immediately downstream from the secondary main on a 480Y/277-volt secondary transformer shall be equipped with ground fault protection unless that circuit breaker is rated 200 amps or less. Each circuit breaker protecting a motor of 100 horsepower or more shall be equipped with ground fault protection. Ground fault protection on motors shall be instantaneous type and ground fault protection on main breakers and feeder breakers shall be equipped with time delay setting and restraint systems. Motor Protection and Control Magnetic-only circuit breakers shall be provided as a branch circuit protection in motor starters for all motors 50 hp and smaller. Branch circuit protection for larger motors shall be provided by thermal magnetic breakers with adjustable magnetic trips. Motor control center type construction shall be used where multiple three-phase motors are located in the same general area. Each motor shall be provided with thermal overload protection in all ungrounded phases. Controller-mounted thermal overload relays shall have external manual reset. Internal temperature detectors embedded in motor windings shall be specified for motors of 100 hp and larger and all motors 10 hp and larger that are powered by an adjustable frequency drive. Multi-function protective relays for overload, phase protection, and ground fault protection shall also be provided on large motors. All motor control circuits shall operate at 120 volts and shall be supplied by individual control power transformers fused both in the primary and secondary sides. Electrical motor starter control shall normally consist of indicating lights, pushbuttons, or switches. Devices connected with process controls, such as timers and auxiliary relays, shall be provided in instrumentation and control panels or operated by a programmable logic controller as part of its internal control logic.

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Appendix C



Panelboards A separate circuit breaker shall be provided for instruments that perform the same function on parallel flow streams, such as DO meters, flow meters, etc. Instruments of different types that are all associated with the same flow stream may be connected to the same branch circuit to simplify the design. Where multiple instruments are connected to a single-branch circuit, a toggle switch shall be provided at each tap to allow each individual instrument to be disconnected from the branch circuit. A common branch circuit shall be provided for all valve and gate operators that are associated with a single-flow stream. Examples: x One circuit per bar screen channel Branch circuits or feeders shall be identified on the drawings with the panelboard and device protecting the individual circuit or feeder. Lighting panelboards shall be surface-mounted, 208Y/120-volt, three-phase, four-wire type with the main circuit breaker sized to match the lighting transformer capacity. Separate panelboards shall be provided to supply power to instruments and control panels where the equipment to be supplied requires a conditioned power supply. Where two 480-volt power supplies are available, an automatic transfer switch shall be provided to supply power to the lighting panelboard transformers from either 480-volt source. Each panelboard shall be equipped with a minimum of 20 percent spare breakers with spaces, bus work, and terminations to complete the standard size panelboard. Panelboard schedules shall show the circuit description, protective device trip rating, number of poles, rating of main lugs or main circuit breaker, neutral bus size, ground bus size, and interrupting rating of breakers. Computer-generated panelboard schedules shall be included in the drawings. Panelboard schedules shall be prepared indicating circuit description, protective device trip rating, number of poles, load in volt-amps by phase, rating of main lugs or main circuit breaker, neutral bus size, ground bus size, and interrupting rating of breakers.

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Appendix C



Convenience Receptacles Duplex receptacles for general service shall be spaced not more than 40 feet apart inside all process buildings and 75 feet apart in outside process areas and shall be located on the surface of walls or columns. Receptacles in outdoor locations and areas subject to washdown shall be weatherproof. Receptacles shall be located as needed in commercial areas. Ground Fault Ground fault systems shall be zero sequence type. Coordination shall be obtained by hard-wired trip restraints (about 2ms restraint). Facilities shall be provided for testing the ground fault circuit by secondary current injection, with or without tripping and for indicating the occurrence of a ground fault. Current and time trip levels shall be adjustable. Ground fault shall be supplied external to the circuit breaker. Motor ground fault shall be an instantaneous trip. Power Factor Power factor correction capacitors shall be applied to all motor starters for motors of 40 hp and larger. Capacitor banks shall generally be located on top of motor control centers. Raceways Specific types of raceway shall be chosen for use in various locations in the facility based on moisture, temperature, exposure to damage, corrosion, voltage, and cost. Separate, concrete-encased, polyvinyl chloride (PVC) conduit, underground duct bank shall be provided for the following systems: x Power wiring above 600 volts; x Power and discrete control wiring below 600 volts; x Process instrumentation analog and communication wiring. Underground raceways that are not installed in a duct bank shall be direct-buried, schedule 40 PVC conduit. The following general guidelines shall be used for raceway sizing, selection, and installation: x Conduit size shall be based on THWN insulation for sizes below No. 6 AWG, and THW insulation for all other wiring 600 volts and below. x The minimum diameter of conduit in all areas shall be 3/4 inch. x Exposed raceways shall be installed in process areas. x Raceways in walls and ceilings in control rooms, offices, and all areas ESD-106

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Appendix C

SAMPLE ELECTRICAL DESIGN CRITERIA MEMO x x x x x x

x

x x


with finished interiors shall be concealed. Embedded and buried nonmetallic conduits shall be converted to metallic conduit before exiting from masonry or earth. The number of conduit bends shall be limited to an equivalent of 270 degrees on long runs. Exterior, exposed conduit shall be aluminum and/or PVC-coated rigid steel. Exterior, underground, direct-buried conduit shall be schedule 40 PVC. Exterior, underground, concrete-encased conduit shall be schedule 40 PVC. Interior, concealed conduit shall be electrical metallic tubing (EMT) in frame construction and finished ceiling spaces, schedule 40 PVC when embedded in concrete or direct-buried in earth. Interior conduit exposed in dry areas shall be steel, except that EMT shall be allowed for lighting circuits more than 4 feet above finished floor. Interior conduit exposed to damp or wet areas shall be aluminum and/or PVC coated rigid steel. Interior conduit exposed to corrosive areas shall be schedule 80 PVC.

Wire And Cable Copper conductors shall be used for all lighting and power wiring of 600 volts and below. Solid conductors shall be used for No.10 AWG and smaller where required by wiring devices. Stranded conductors shall be used for other applications. o

The current carrying capacity of conductors shall be based on 75 C insulation ratings. Conductors No. 6 AWG and smaller shall have THHN/THWN insulation; larger conductors shall have XHHW insulation. Individual No. 14 AWG conductors shall be used for discrete control circuits, unless it is practical to use multi-conductor cables to group control circuits. Twisted-shielded pair control cable No. 16 AWG with an aluminum mylar tape shield shall be used for analog signals. Multi-pair cables shall be used where grouping of circuits is practical. Conductors above 600 volts shall be 19-strand copper with ethylene-propylene polymer (EPR) insulation, copper tape shield and PVC outer jacket.

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Appendix C



Motor Control Centers MCCs shall use NEMA 1B wiring. Limiters shall be shown where necessary. Overloads will be non-ambient-compensated unless such compensation is needed, for instance, at submerged pumps. MCCs shall be 20 inches deep. All solenoid valves, thermal devices, etc., that need to be operated when the motor is on shall be powered from the motor starter CPT. Where this is done, the need for additional CPT capacity shall be called out. A minimum of 5 percent spares and 10 percent spaces shall be provided. Allow space for at least one future section at each MCC. Switchboards Switchboards shall be similar to Square D Power Style with individually mounted, molded case circuit breakers that have solid state trip elements. See the manufacturers data contained hereinafter for additional information. Grounding Load centers shall be bonded to a grounding electrode, which may consist of a building steel column that is bonded to the underground rebar or the nearest available effectively grounded metal water pipe. In addition, ground rods shall be driven outside the building to supplement the ground electrode. Grounding electrodes of ground mats or embedded rods and cables shall have a maximum resistance to ground of 1 ohm. A minimum of No. 2/0 insulated copper cable shall be used for interconnecting ground rods and connection to equipment. The parts of all electrical equipment, devices, panelboards, and metallic raceways that do not carry current shall be connected to the ground conductors. The transformer neutrals of wye-connected transformers shall be solidly grounded through a grounding conductor connected to the grounding system. A ground wire shall be installed in all raceways that contain power conductors at any voltage. Lighting Lighting levels in all areas of the plant shall be calculated following the procedures recommended in the Illumination Engineering Society (IES) handbook. In general, the following minimum foot-candle level shall be provided:

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Appendix C

SAMPLE ELECTRICAL DESIGN CRITERIA MEMO Area


Foot-Candle

Office

70

Process, inside

50

Process, outside

5

Storage, inside

10

Walkway

5

General site

1

The following general types of light service shall be used to provide the proposed foot-candle levels: AreaLight Service Office

Fluorescent

Process, inside to 12 feet mounting height

Fluorescent

Process, above 12 feet mounting height

High pressure sodium or metal halide

Storage, inside

Fluorescent

Walkway, inside

Fluorescent

Walkway, outside

High pressure sodium

General site

High pressure sodium

Transformers Transformers to supply 208Y/120 volt requirements shall be dry type and suitable for the area in which they are to be located. Transformers that include a small panelboard in the same enclosure shall not be used, A small transformer with a separate panelboard shall be used in every case. Transformers to supply 480 volt 3-phase and 4160 volt 3-phase shall be of the pad mount type where located outdoors and of the dry type where located indoors.

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Appendix C



Miscellaneous Systems Fire alarm systems shall be included in buildings as required by applicable codes. INTERFACES Facility Each facility shall have designated interface points for connection with conductors that leave the facility. For each facility, make a list showing where the interfaces are. x Power Interfaces. Power interfaces shall be done at an assembly or device and shall not require a junction box. x Discrete Instrument and Control Interfaces. Where all discrete I&C circuits that leave a facility are in a single assembly, that assembly shall be used as the interface. Where discrete I&C circuits that leave a facility come from several assemblies, a TJB shall be installed for the interface (see Figure ___). x Analog Instrument and Control Interfaces. Where all analog I&C circuits that leave a facility are in a single assembly, that assembly shall be used as the interface. Where analog I&C circuits that leave a facility come from several assemblies, a JB or TJB (if conversion to a multiconductor cable is required) shall be installed for the interface. CALCULATIONS REQUIRED Calculations shall be done in an orderly manner either on a desktop PC computer or on computation paper. Each sheet shall have the date on which the computations were made, the project number, and the designers name. All information used in the preparation of the design shall be kept in a notebook with tabs to properly divide the different items such as telco memos, comps, letters, equipment data sheets, etc. Each computation shall clearly identify the facility for which the calculations are being made and the type of computation that is being performed. Copies of all calculations shall be sent to project lead electrical engineer as they are completed for his review and filing. At the completion of the project, all pertinent information shall be assembled in a single set of notebooks for inclusion in the project files. The computations listed below are the minimum that need to be documented. All calculations shall be reviewed before the related drawings are drafted.

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Appendix C



Wire Sizing Take into account wet/dry areas and ambient temperatures—see attached form for a guide. Show wiring sizing for all services, feeders, and large branch circuits. Calculations shall include a summary of all loads to be served where there is more than one load. Calculations for feeders to panelboards shall reference the specific panelboard being supplied and a copy of the panel schedule with all loads indicated shall be included with the calculations. Primary and secondary feeders to/from dry type transformers shall be sized in accordance with the attached transformer table and the proper sized main breaker shall be shown in the panelboard that is served from the transformer. Dry Type Transformers Include a list of all branch circuit panelboards to be supplied and the connected load on each panel. Demand and diversity factors that are allowed by the NEC may be used for sizing transformers that supply loads in areas that are not process related, but transformers in other areas shall be adequately sized to supply the total connected load connected to the process. Pad Mounted and Unit Substation Transformers All power supply transformers shall be sized to supply the total load that is normally connected to the transformer's secondary bus without exceeding the air-cooled rating of the transformer. Where there are three MCC buses, it shall be assumed that the third MCC bus can be "normally connected" to either transformer. Each transformer shall also be able to carry the total load of the load center that would be expected to be operating during peak flow conditions without exceeding the transformer's overload rating, assuming that one transformer has failed. Voltage Drop Prepare steady-state voltage drop calculations for all heavily loaded and/or long branch circuits and feeders using the attached "Voltage Drop Calculation Data." Base calculations for motor circuits on an 80 percent power factor. Motor starting voltage drop calculations shall be shown for all motors that exceed 20 percent of the rating of the serving transformer. Steady state voltage drop shall be limited to the values listed in the Design Criteria with not more than 2 percent drop on feeder. Motor starting voltage drop shall be limited to 20 percent.

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Appendix C



Branch Circuits Connected load and NEC requirements shall be used for sizing branch circuit breakers and conductors. A minimum wire size of No. 12 AWG copper shall be used for lighting and receptacle branch circuits. No. 10 AWG shall be used where the first convenience receptacle is more than 75 feet from the panelboard. In general, 120 volt lighting branch circuit load shall be used for up to 1800 voltamps. 120 volt lighting loads shall be connected to circuits separate from receptacles except in storage rooms where the lights may be connected to receptacle circuits or vice versa. Branch circuit shall be limited to five duplex receptacles in process areas and six duplex receptacles in office areas. Special areas may require further reduction in number of receptacles per circuit. Conduit Size Calculations shall be included for sizing of all conduits that are not covered by the table of conduit sizes included hereinafter. Conduit fill shall not exceed that allowed by the NEC when all conductors, including the ground conductor, are included in the calculation assuming that ground conductors have TW insulation and phase conductors have THW insulation. Power Factor Correction Calculations shall be made for the sizing of all power correction capacitors. The calculations shall include a statement showing all assumptions that are made to make the calculation. If tables are used, a copy of the table used with appropriate values marked, shall be included in the calculation section of the notebook. Lighting Calculations may be in any form. For small areas, a statement that "so many" lights of "such" a size will do the job, and is all that is required. For larger areas, use the "Zonal Cavity Calculations" form attached. The foot-candle level resulting from the actual fixtures to be installed shall be documented. Fault Study and Coordination This should take into account future loads and changed conditions. Presume the utility is an infinite bus unless better information can be obtained.

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Appendix D

ENCLOSURE TYPES


NEMA Type 1, General Purpose. Enclosures intended for indoor use primarily to provide a degree of protection against limited amounts of falling dirt. NEMA Type 2, Dripproof. Enclosures intended for indoor use primarily to provide a degree of protection against limited amounts of failing water and dirt. Enclosures have provisions for drainage. If provision is made for the entrance of conduit at the top, it consists of a conduit hub or equivalent. NEMA Type 3, Dusttight, Raintight, and Sleet- (Ice-) Resistant. Enclosures intended for outdoor use primarily to provide a degree of protection against rain, sleet, windblown dust and damage from external ice formation. Enclosures have conduit hubs or equivalent provision for watertight connection at the conduit entrance. NEMA Type 3R, Rainproof and Sleet- (Ice-) Resistant. Enclosures intended for outdoor use primarily to provide a degree of protection against rain, sleet, and damage from external ice formation. NEMA Type 3S, Dusttight, Raintight, and Sleetproof (Iceproof) Enclosures intended for outdoor use primarily to provide a degree of protection against rain, sleet, windblown dust and to provide for operation of external mechanisms when ice laden. Enclosures have conduit hubs or equivalent provision for watertight connection at the conduit entrance, mounting means external to the equipment cavity, and provision for locking. NEMA Type 4, Watertight, Dusttight, and Sleet-Resistant. Enclosures intended for indoor or outdoor use primarily to provide a degree of protection against windblown dust and rain, splashing water, hose-directed water and damage from external ice formation. Enclosures have conduit hubs or equivalent provision for watertight connection at the conduit entrance and mounting means external to the equipment cavity. NEMA Type 4X, Watertight, Dusttight, Sleet- and Corrosion Resistant: Same provisions as Type 4 enclosure, and in addition, are corrosion-resistant. NEMA Type 6, Submersible, Watertight, Dusttight, and Sleet- (Ice-) Resistant. Enclosures intended for indoor or outdoor use primarily to provide a degree of protection against hose-directed water, and the entry of water during occasional temporary submersion at a limited depth and damage from external ice formation. Enclosures have conduit hubs or equivalent provision for watertight connection at the conduit entrance and mounting means external to the equipment cavity. NEMA Type 6P, Submersible, Watertight, Dusttight, and Sleet- (Ice-) Resistant. Same provisions as Type 6 enclosure except for protection against entry of water during prolonged submersion at a limited depth.

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Appendix D

ENCLOSURE TYPES


NEMA Type 7, Class I, Group A, B, C, or D Hazardous Locations, Air-Break. Enclosures intended for indoor use in locations classified as Class I, Division 1, Groups A, B, C or D hazardous locations as defined in the National Electric Code (NFPA 70). Enclosures are designed to withstand the pressures of an internal explosion and not ignite an explosive mixture outside the enclosure. Equipment within the enclosure shall be able to interrupt in a flammable atmosphere. Enclosures are commonly referred to as explosion-proof. NEMA Type 8, Class I, Group A, B, C, or D Hazardous Locations, Oil-Immersed. Enclosures intended for indoor or outdoor use in locations classified as Class I, Division 2, Groups A, B, C or D hazardous locations as defined in the National Electric Code (NFPA 70). Enclosures are designed such that the enclosed equipment is oil-immersed and can operate at rated voltage and most severe current conditions in the presence of flammable gas-air mixtures without igniting these mixtures. Enclosures are commonly referred to as oil immersed. NEMA Type 9, Class II, Group E, F, or G Hazardous Locations, Air-Break. Enclosures intended for indoor use in locations classified as Class II, Division I, Groups E, F and G hazardous locations as defined in the National Electric Code (NFPA 70). Enclosures prevent the ingress of hazardous dust and are commonly referred to as dust-ignition proof. NEMA Type 10. Nonventilated enclosures constructed for mine use and designed to meet the requirements of the Mine Safety and Health Administration. NEMA Type 11, Corrosion-Resistant and Dripproof, Oil-Immersed. Enclosures intended for indoor use to protect the enclosed equipment against dripping, seepage, and external condensation of corrosive liquids by providing for immersion of equipment in oil. NEMA Type 12, Industrial Use, Dusttight, and Driptight. Enclosures intended for indoor use to protect the enclosed equipment against fibers, flyings, lint, dust, and external condensation of noncorrosive liquids. Enclosures have no holes, conduit knockouts or conduits openings, except that oiltight or dusttight mechanisms may be mounted through holes in the enclosure when provided with oil-resistant gaskets. NEMA Type 13, Oiltight and Dusttight. Nonventilated enclosures intended for indoor use primarily to house control-circuit devices such as limit switches, foot switches, pushbutton, selector switches, and pilot lights and to protect these devices against lint and dust, seepage, external condensation, and spraying of water, oil, or coolant. All conduit openings have provisions for oiltight conduit entry.

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Appendix E

MOTOR ENCLOSURE TYPES


OPEN MACHINE: ventilation openings permit passage of external cooling air over and around the winding of the machine DRIP-PROOF MACHINE: ventilation openings are so constructed that successful operation is not interfered with when drops of liquid or solid particles strike or enter the enclosure at any angle from 0 to 15 degrees downward from the vertical. SPLASH-PROOF MACHINE: ventilation openings are constructed so that successful operation is not interfered with when drops of liquid or solid particles strike or enter the enclosure at any angle not greater than 100 degrees downward from the vertical. SEMIGUARDED MACHINE: ventilation openings in the machine, usually in the top half, are guarded as in the case of a "guarded machine," but the others are left open. GUARDED MACHINE: all openings giving direct access to live metal or rotating parts are limited in size by structural parts or by screens, baffles, grilles, expanded metal, or other means to prevent accidental contact with hazardous parts. DRIP-PROOF GUARDED MACHINES: a drip-proof machine with guarded ventilation openings. OPEN EXTERNALLY VENTILATED MACHINE: ventilated by means of a separate motor-driven blower mounted on the machine enclosure. OPEN PIPE VENTILATED MACHINE: openings for the admission of the ventilation are so arranged that inlet ducts or pipes can be connected to them. Machine shall be self-ventilated or force-ventilated, external from and not a part of the machine. WEATHER PROTECTED MACHINE TYPE I: ventilation passages constructed so as to minimize the entrance of rain, snow, and airborne particles. WEATHER PROTECTED MACHINE TYPE II: ventilation passages at both intake and discharge are arranged so that high velocity air and airborne particles blown into the machine by storms or high winds can be discharged without entering the internal ventilating passages. TOTALLY ENCLOSED MACHINE: enclosed to prevent the free exchange of air between the inside and outside of the enclosure but not sufficiently enclosed to be termed airtight.

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Appendix E



TOTALLY ENCLOSED NONVENTILATED MACHINE: totally enclosed machine that is not equipped for cooling by means external to the enclosed parts. TOTALLY ENCLOSED FAN-COOLED MACHINE: equipped for exterior cooling by means of a fan or fans integral with the machines but external to the enclosed parts. EXPLOSION-PROOF MACHINE: enclosure designed and constructed to withstand an explosion of a specified gas or vapor that may occur within the enclosure and to prevent ignition of the specified gas or vapor surrounding the machine by sparks, flashes, or explosions of the specified gas or vapor. DUST IGNITION-PROOF MACHINE: enclosure designed and constructed in a manner that will exclude ignitable amount of dust or amounts that might affect performance or rating, and which will not permit arcs, sparks, or heat to cause ignition of exterior accumulations or atmospheric suspensions of a specific dust. WATERPROOF MACHINE: constructed so that it will exclude water in the form of a stream from a hose, except that leakage may occur around the shaft that provides for automatic drainage. TOTALLY ENCLOSED PIPE VENTILATED: constructed with openings so arranged that when inlet and outlet ducts or pipes are connected to them there is no free exchange of the internal air and the air outside the enclosure may be self-ventilated or force-ventilated. TOTALLY ENCLOSED WATER COOLED MACHINE: cooled by circulating water, with the water or water conductors coming in direct contact with machine parts. TOTALLY ENCLOSED WATER-AIR-COOLED MACHINE: cooled by circulating air which, in turn, is cooled by circulating water. Machine is provided with a water-cooled heat exchanger for cooling the internal air and a fan or fans, either integral with the rotor shaft or separate, for circulating the internal air. TOTALLY ENCLOSED AIR-TO-AIR COOLED MACHINE: cooled by circulating the internal air through a heat exchanger which, in turn, is cooled by circulating external air. Machine is provided with an air-to-air heat exchanger for cooling the internal air and a fan or fans, either integral with the rotor shaft or separate, for circulating the internal air and a fan or fans, either integral with the rotor shaft or separate but external to the enclosing part or parts, for circulating the external air.

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Appendix E



TOTALLY ENCLOSED FAN-COOLED GUARDED MACHINE: all openings giving direct access to the fan are limited by size or design of the structural parts, and have screens, grilles, expanded metal, etc. to prevent accidental contact with the fan. TOTALLY ENCLOSED AIR-OVER MACHINE: intended for exterior cooling by ventilation external to the machine.

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Appendix F

MOTOR DESIGN TYPES


The polyphase induction motor shall be of either the squirrel-cage or the wound-rotor type. The squirrel-cage induction motor has been classified by National Electrical Manufacturers Association (NEMA) Tests and Performance-AC (MG1-1987) according to the following designs. Design A. A Design A motor is a squirrel-cage motor designed to withstand full-voltage starting and to develop locked-rotor torque. It has a breakdown torque as shown in Table MG1-12-39. It has a locked-rotor current higher than the value shown in Table MG1-12-35 and a slip at rated load of less than 5 percent. Design A motors are usually used for applications where extremely high efficiency and extremely high full-load speed are required. Therefore, Design A motors tend to be special motors. Design B. A Design B motor is a squirrel-cage induction motor designed to withstand full-voltage starting, developing locked-rotor and breakdown torques adequate for general application as specified in Tables MG1-12-38.1 and MG1-12-39, drawing locked-rotor current not to exceed the values shown in Table MG1-12-35, and having a slip at rated load of less than 5 percent. Motors with 10 and more poles may have a slip slightly greater than 5 percent. Design B motors are the standard general-purpose motors used where low locked-rotor current and moderate locked-rotor torque are required along with high full-load speed and efficiency. Design C. A Design C motor is a squirrel-cage motor designed to withstand full-voltage starting, developing locked-rotor torque for special high-torque applications up to the values shown in Table MG1-12-38.2, breakdown torque up to the values shown in Table MG1-12-39.2, with locked-rotor current not to exceed the values shown in Table MG1-12-35, and having a slip at rated load of less than 5 percent. Design D. A Design D motor is a squirrel-cage motor designed to withstand full-voltage starting, developing high locked-rotor torque as shown in Table MG1-12-38.2, with locked-rotor current not greater than that shown in Table MG1-12-35, and having a slip at rated load of 5 percent or more. Design F. A Design F motor is a squirrel-cage motor designed to withstand full-voltage starting, developing low locked-rotor torque as shown in Table MG1-12-38.1 with breakdown torque as shown in Table MG1-12-38.2, with locked-rotor current not to exceed the values shown in Table MG1-12-35, and having a slip at rated load of less than 5 percent.

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Appendix F

MOTOR DESIGN TYPES


The following figure shows typical speed-torque curves of NEMA design-class squirrel cage motors.

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Appendix G

MOTOR TORQUE DEFINITIONS


The following terms are commonly used to describe motor torque. Full load torque – Torque necessary to produce rated horsepower at full-load speed. Locked-rotor (starting) torque – Minimum torque which the motor will develop at rest for all angular positions of the rotor, with rated voltage applied at rated frequency. Pull-up torque – Minimum torque developed by the motor during the period of acceleration from rest to the speed at which breakdown torque occurs. For motors which do not have a definite breakdown torque, the pull-up torque is the minimum torque developed up to rated speed. Breakdown torque – Maximum torque which the motor will develop with rated voltage applied at rated frequency, without an abrupt drop in speed. Pull-out torque (synchronous motor) – Maximum sustained torque which the motor will develop at synchronous speed with rated voltage applied at rated frequency and with normal excitation. Pull-in torque (synchronous motor) – Maximum constant torque under which the motor will pull its connected inertia load into synchronism, at rated voltage and frequency, when its field excitation is applied.

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G-1

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Appendix H

STANDARD SPECIFICATIONS FOR THE IDENTIFICATION OF ELECTRICAL CURRENT CARRYING CONDUCTORS


The specification is provided by the Treatment Plant Design Team. CABLE IDENTIFICATION Conductor and multiconductor cables should be identified at each end of the installed cable. Cable tags and fastening devices shall be made of nonconductive materials. Cable tab marking should be permanent type and waterproof. The cable number should be show on single-line diagrams, wiring diagrams, wire list, instrument-loop diagrams, and panel-wiring diagrams. The cable number should be constructed as follows:

1.

Feeder Cable From Unit Substation or Distribution Load-Center. a. IP-1

(without suffix letter)

b. IP-1 A

(with suffix letter) Suffix letter as required (A,B,C,…etc.) Feeder number from unit substation or distribution loadcenter (1,2,3…etc.) MSDS transformer’s secondary cable designation.

2.

Feeder Cable from Motor Control Center or Power Distribution Panel. a. 1P1-1


b. 1P1-1 A

(with suffix letter) Suffix letter as required (A,B,C,…etc.) Feeder number from motor control center or power distribution panel (1,2,3…etc.) Motor control center or power distribution panel designation.

3.

Branch Circuit Cable From Lighting and Receptacle Panel. a. 2L-1

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H-1

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Appendix H

STANDARD SPECIFICATIONS FOR THE IDENTIFICATION OF ELECTRICAL CURRENT CARRYING CONDUCTORS b. 2L-1 A


(with suffix letter) Suffix letter as required (A,B,C,…,etc.) Lighting or receptacle circuit number (1,2,3…etc.) Lighting and receptacle panel designation (“L” denotes lighting and receptacle cable or conductor)

4.

Control Cable of Motor Starter or Controller. a. 1C1-1


b. 1C1-1 A

(with suffix letter) Suffix letter as required (A,B,C,…,etc.) Feeder number from power source panel. Motor control center or power distribution panel designation, except “C,” which denotes “Control” is substituted for power “P” or to any power designated letters. Typical for all feeder-source-panel with control cable or conductor.)

5.

Control Cable of Instrumentation Equipment with Contract Closure a. PS500C


b. PS500 C A

(with suffix letter) Suffix letter as required (A,B,C,…,etc.) Denote “Control” cable. Instrument tag number as show on the P&ID’s without suffix number.

ESD-106

c. LI302C-1


d. LI302C-1 A

(with suffix letter)

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Appendix H



Suffix letter as required (A,B,C,…,etc.) Instrument tag number’s suffix number as required (1,2,3…etc) Control cable designation without suffix number.

6.

Instrumentation Cable of Instrumentation Equipment with Analog Signal a. I-PS500


b. I-PS500 A

(with suffix letter) Suffix letter as required (A,B,C,…etc.) Instrument tab number as shown on the P&ID’s without suffix number. Denotes “Instrumentation” cable.

c. I-LI302-1


d. I-LI302-1 A

(with suffix letter) Suffix letter as required (A,B,C,…etc.) Instrument tag number’s suffix number as required (1,2,3,..etc.) Instrumentation cable designation without suffix number. Denotes “Instrumentation” cable.

Note: See Figure H-1 and Figure H-2 for samples.

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Appendix H


Figure H-1.

ESD-106


Examples of Power Feeder Cable Identifications for Water Treatment Plant Section

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Appendix H


Figure H-2.

ESD-106


Examples of Control and Instrumentation Cable Identifications for Water Treatment Plant Section

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Appendix H



ELECTRICAL BRANCH HYDRO PLANT DESIGN SECTION STANDARD SPECIFICATION FOR THE IDENTIFICATION OF ELECTRICAL CURRENT 1.0

2.00

DEFINITIONS: Cable: A current carrying conductor/ conductors enclosed in an insulating sheath and bound by an outer jacket of insulating material. Conductor: A single current carrying material enclosed by an insulating jacket.

3.0.

INSTALLATION REQUIREMENTS:

3.10

Cable identification tags shall be non-metallic material and permanently affixed to outer cable jacket. Identification tags should be affixed within 6” of conductor separation from outer jacket except as noted.

3.20

ESD-106

SCOPE: This standard provides the means of identifying electrical current Carrying conductors on single line diagrams, wiring diagrams, wire lists. Instrument loop diagrams, and internal/external panel diagrams. Also provided is the installation requirements for cable identification tags.

3.21

EXCEPTIONS: I. where taping or shielding is required the tag shall be placed as close to the termination point as physically possible.

3.30

All conductors and multi-conductor cables identified on design documents as requiring identification tags should have a Thomas & Betts WSL selflaminating vinyl marker, or equal attached or shrink wrapped to the cable.

3.31

single conductors and individual conductors of multi-conductor cables should be identified with a Thomas & Betts type WWSL selflaminating vinyl marker, or equal attached or shrink wrapped to the conductor indicating the point of termination.

3.32

All conductor voltage levels shall be identified by the following color code in Table-A.

BACKGROUND COLOR

TABLE - A CHARACTER COLOR

RED ORANGE BLUE BLACK BROWN GREEN

WHITE BLACK WHITE WHITE WHITE WHITE

H-6

VOLTAGE LEVEL 12KV AND UP 4.16KV 480V 240V 120V SIGNAL

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Appendix H



4.0.0

IDENTIFICATION REQUIREMENTS:

4.1.0

All cables that require identification should be identified by the following alpha-numeric code as shown in Figure H-3

4.1.1

The alpha-numeric code shall be used on all design documents where cable identification is required

4.2.0

UNIT OR EXPANSION NUMBER The unit or expansion number indicates the phases of the project. This number or letter will increase as subsequent phases of the project are started.

4.2.1

ASSOCIATED PLANT SYSTEM The associated plant system indicates the system that the cable is related to. See page H-10 for a sample listing of plant system.

4.2.2

EQUIPMENT NUMBER The equipment number or letter identifies a particular piece of equipment that is related to the associated plant system.

4.2.3

CABLE TAG NUMBER 00 THROUGH 99 The cable tag number identifies a particular cable that is related to a specific piece of equipment located within a particular plant system.

X XX X X X CABLE TAG NUMBER 00 THROUGH 99 EQUIPMENT NUMBER ASSOCIATED PLANT SYSTEM UNIT OR EXPANSION NUMBER

Figure H-2.

ESD-106

Cable Identification

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Appendix H


ESD-106


Figure H-3.

Identification of A Multi-Conductor Cable

Figure H-4.

Identification of A Single-Conductor Cable

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Appendix H



ASSOCIATED PLANT SYSTEMS CABLE CODES MECHANICAL SYSTEMS

ELECTRICAL SYSTEMS

AD

ALUM DISTRIBUTION

SS

STATION SERVICE

BD

BASIN DEWATERING

US

UNIT SUBSTATION

BP

BACKWASH POLYMER

MC

MOTOR CONTROL CENTER

CI

CHEMICAL INJECTION

ST

STATION TRANSFER

CD

CHLORINE DISTRIBUTION

UT

UNIT SUB-STATION

DP

DRY POLYMER

MT

MCC TRANSFORMER

EQ

EFFLUENT WATER QUALITY

L1

LIGHTING PANEL 1

FA

FILTER AID DISTRIBUTION

D1

DISTRIBUTION PANEL 1

FB

FLOCCULATION BASINS

FD

FLOOR DRAINS

FI

FILTER OPERATION

FO

FOAM ABATEMENT

FL

FLOCCULENT AID DISTRIBUTION

FW

FIRE WATER DISTRIBUTION

GW

GRAY WATER

IW

INDUSTRIAL WATER

IQ

INFLUENT WATER QUALITY

PA

PLANT AIR

PI

PLANT INFLUENT

SD

SUBDRAINS

SP

SPARGER PUMPS

SW

SURFACE WASHWATER

TB

TRAVELING BRIDGE

WP

PORTABLE WATER PUMPS

WS

WATER SAMPLING

WW

WASHWATER

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Appendix H



XXXXXX

BOX TAG NUMBER BOX IDENTIFICATION UNIT OR EXPANSION NUMBER TYPICAL MANHOLE IDENTIFICATION

1MH123 TYPICAL MANHOLE IDENTIFICATION

1MHH123 TYPICAL PULLBOX IDENTIFICATION

1PB123 TYPICAL JUNCTION BOX IDENTIFICATION

1JB123 TYPICAL TERMINATION BOX IDENTIFICATION

1TB123 Figure H-5.

ESD-106

Typical Box Identification

H-10

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Appendix H



X X X X X X

COLUMNS 01 TO 99

01

02

03

04

05

1 1A1101

1A1102 1A1103 1A1104 1A1107

2 1A1201 ROWS 1 TO 9

1A1202 1A1203 1A1204 1A1205

3 1A1301

1A1302 1A1303 1A1304 1A1305

4 1A1401

1A1402 1A1403 1A1404 1A1405

5 1A1501 1A1502 1A1503 1A1504

1A1505

TYPICAL DUCT ALPHA-NUMERIC CODE Figure H-6. ESD-106

Typical Duct Bank Identification

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Electrical Design Manual: Metropolitan Water District Of Southern California

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