Construction Electrician Apprenticeship Program Level 3 Line G: Install Low-Voltage Distribution Systems. Learning guide G-2

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1 G-2 Construction Electrician Apprenticeship Program Level 3 Line G: Install Low-Voltage Distribution Systems Learning guide G-2 Install service equipment

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3 Foreword The Industry Training Authority (ITA) is pleased to release this major update of learning resources to support the delivery of the BC Electrician Apprenticeship Program. It was made possible by the dedicated efforts of the Electrical Articulation Committee of BC (EAC). The EAC is a working group of electrical instructors from institutions across the province and is one of the key stakeholder groups that supports and strengthens industry training in BC. It was the driving force behind the update of the Electrician Apprenticeship Program Learning Guides, supplying the specialized expertise required to incorporate technological, procedural and industry-driven changes. The EAC plays an important role in the province s post-secondary public institutions. As discipline specialists the committee s members share information and engage in discussions of curriculum matters, particularly those affecting student mobility. ITA would also like to acknowledge the Construction Industry Training Organization (CITO) which provides direction for improving industry training in the construction sector. CITO is responsible for organizing industry and instructor representatives within BC to consult and provide changes related to the BC Construction Electrician Training Program. We are grateful to EAC for their contributions to the ongoing development of BC Construction Electrician Training Program Learning Guides (materials whose ownership and copyright are maintained by the Province of British Columbia through ITA). Industry Training Authority January 2011 Disclaimer The materials in these Learning Guides are for use by students and instructional staff and have been compiled from sources believed to be reliable and to represent best current opinions on these subjects. These manuals are intended to serve as a starting point for good practices and may not specify all minimum legal standards. No warranty, guarantee or representation is made by the British Columbia Electrical Articulation Committee, the British Columbia Industry Training Authority or the Queen s Printer of British Columbia as to the accuracy or sufficiency of the information contained in these publications. These manuals are intended to provide basic guidelines for electrical trade practices. Do not assume, therefore, that all necessary warnings and safety precautionary measures are contained in this module and that other or additional measures may not be required.

4 Acknowledgements and Copyright Copyright 2011, 2014 Industry Training Authority All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or digital, without written permission from Industry Training Authority (ITA). Reproducing passages from this publication by photographic, electrostatic, mechanical, or digital means without permission is an infringement of copyright law. The issuing/publishing body is: Crown Publications, Queen s Printer, Ministry of Citizens Services The Industry Training Authority of British Columbia would like to acknowledge the Electrical Articulation Committee and Open School BC, the Ministry of Education, as well as the following individuals and organizations for their contributions in updating the Electrician Apprenticeship Program Learning Guides: Electrical Articulation Committee (EAC) Curriculum Subcommittee Peter Poeschek (Thompson Rivers University) Ken Holland (Camosun College) Alain Lavoie (College of New Caledonia) Don Gillingham (North Island University) Jim Gamble (Okanagan College) John Todrick (University of the Fraser Valley) Ted Simmons (British Columbia Institute of Technology) Members of the Curriculum Subcommittee have assumed roles as writers, reviewers, and subject matter experts throughout the development and revision of materials for the Electrician Apprenticeship Program. Open School BC Open School BC provided project management and design expertise in updating the Electrician Apprenticeship Program print materials: Adrian Hill, Project Manager Eleanor Liddy, Director/Supervisor Beverly Carstensen, Dennis Evans, Laurie Lozoway, Production Technician (print layout, graphics) Christine Ramkeesoon, Graphics Media Coordinator Keith Learmonth, Editor Margaret Kernaghan, Graphic Artist Publishing Services, Queen s Printer Sherry Brown, Director of QP Publishing Services Intellectual Property Program Ilona Ugro, Copyright Officer, Ministry of Citizens Services, Province of British Columbia To order copies of any of the Electrician Apprenticeship Program Learning Guide, please contact us: Crown Publications, Queen s Printer PO Box 9452 Stn Prov Govt 563 Superior Street 2nd Flr Victoria, BC V8W 9V7 Phone: Toll Free: Fax: crownpub@gov.bc.ca Website: Version 1 Revised, April 2014 New, October 2012

5 LEvel 3, Learning guide G-2: Install service equipment Learning Objectives Learning Task 1: Describe the features of three-phase, low-voltage distribution systems Self-Test Learning Task 2: Describe service entrance equipment Self-Test Answer Key Construction Electrician Apprenticeship Program: LEvel 3 5

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7 Learning Objectives G-2 Learning Objectives The learner will be able to determine low-voltage, three-phase service equipment requirements. Activities Read and study the topics of Learning Guide G-2: Install Service Equipment. Complete Self-Tests 1 and 2. Check your answers with the Answer Key provided at the end of this Learning Guide. Resources Canadian Electrical Code, Part 1 (current edition); Published by the Canadian Standards Association Requirements for Secondary Metering Installations; Published by BC Hydro Canadian Electrical Code Handbook; Published by the Canadian Standards Association Construction Electrician Apprenticeship Program: Level 3 7

8 BC Trades Modules We want your feedback! Please go the BC Trades Modules website to enter comments about specific section(s) that require correction or modification. All submissions will be reviewed and considered for inclusion in the next revision. SAFETY ADVISORY Be advised that references to the Workers Compensation Board of British Columbia safety regulations contained within these materials do not/may not reflect the most recent Occupational Health and Safety Regulation. The current Standards and Regulation in BC can be obtained at the following website: Please note that it is always the responsibility of any person using these materials to inform him/herself about the Occupational Health and Safety Regulation pertaining to his/her area of work. Industry Training Authority January Construction Electrician Apprenticeship Program: Level 3

9 Learning Task 1: Describe the features of three-phase, low-voltage distribution systems The 120 V/240 V, three-wire, single-phase distribution system studied in Level 1, Learning Guide D-2: Analyze DC Circuits has definite limitations. It is generally restricted to applications where the total load is small such as residential, small stores or schools and other very small commercial buildings. This learning task discusses two systems more suitable for commercial or industrial use. They are the three-phase, four-wire (wye) system and the three-wire delta system. Three-phase, four-wire (wye) system The most widely used three-phase power distribution system is the three-phase, four-wire system. This system is commonly used to supply 120 V/208 V, 277 V/480 V, and 347 V/600 V for commercial and industrial loads. A 120 V/208 V system is often used to supply a combination of lighting and power loads, providing 120 V line-to-neutral for lighting and low power loads, and 208 V line-to-line for threephase motors and other power loads (see Figure 1). This system offers substantial economy over the 120 V/240 V single-phase system in that: The amount of copper required to deliver a given amount of load power is reduced to 75%. Three-phase equipment such as motors and transformers is less costly. Transformer secondary A B 120 V 208 V Heater 3 φ motor 120 V C 120 V Neutral Figure V/208 V, three-phase, four-wire (wye) system The most popular system for most large commercial and industrial power distribution is the 347 V/600 V system, which can supply both three-phase and single-phase loads. Construction Electrician Apprenticeship Program: LEvel 3 9

10 Learning Task 1 G-2 CEC Rules for three-phase, four-wire systems CEC Rule This CEC rule specifies that the neutral wire connected to the star point must be white or natural grey. CEC Rule The three other conductors, called the line wires A, B and C, must be colour-coded in the following manner: Phase A = red Phase B = black Phase C = blue CEC Rule The colour of the identified circuit conductor (the neutral) must be continuous throughout its length for conductors up to AWG No. 2. CEC Rule Insulated neutral conductors larger than No. 2 shall be suitably labelled or otherwise clearly marked (usually with white tape) at each end at the time of installation, so that they can be readily identified. Three-phase, three-wire delta system The three-wire delta system is commonly used in commercial and industrial buildings with substantial motor loads. Common system voltages available are 240 V, 480 V and 600 V threephase. A three-phase, three-wire delta system is shown in Figure 2. - Figure 2 Three-phase, three-wire (delta) system There are two key advantages to using the three-phase, three-wire ungrounded system: 1. The cost of installing the fourth conductor (neutral) from the transformer is eliminated. 2. A single ground fault on the system will allow plant operations and production to continue (minimizing interruptions) during the time the fault is located and removed. 10 Construction Electrician Apprenticeship Program: Level 3

11 Learning Task 1 G-2 With a grounded system, the fault will immediately trip the affected circuit, and shut down plant operations in that area. Grounding and bonding (CEC Rule ) Grounding and bonding conductors for circuits, equipment or conductor enclosures must meet four basic requirements: 1. The path to ground must be permanent and continuous. 2. The grounding conductor must be of sufficient size to conduct any predictable fault current for the length of time before the overcurrent device acts. 3. The ground path impedance shall be low enough that a dangerous voltage cannot appear. This is a consideration in high-voltage systems (dealt with in Section 36). 4. The impedance of the ground fault path must be low enough to operate the overcurrent device as quickly as possible (as most overcurrent devices have an inverse time characteristic). Shock hazards and safety The main purpose of grounding is for safety. The Canadian Electrical Code (CEC Rule ) states that grounding and bonding must be done in such a manner to essentially serve the following purposes: To protect life from the danger of electric shock and property from damage. To limit voltages on circuits when exposed to higher voltages than what the circuit was designed for. In general, to limit AC circuit voltages-to-ground to 150 V or less on circuits supplying interior wiring systems. To facilitate the operation of electrical apparatus and systems. To limit the voltage on a circuit when exposed to lightning. It is intended that the grounding/bonding system of all electrical installations provides adequate protection for people and for buildings. Grounding and bonding prevents electric shock, which could result when current leaks to enclosures, raceways or other exposed metal. A system is grounded to limit the possible voltage that can occur between current-carrying conductors and ground. This provides insurance against undue stressing of the insulation. The grounding/bonding system provides a path for fault current, which ensures the operation of protective devices in the event of a fault or circuit failure and prevents the possibility of arcing or overheating, which could occur where a fault current seeks a random path to ground. A path is also provided for electric current resulting from a lightning strike or from accidental contact with another system. Now do Self-Test 1 and check your answers. Construction Electrician Apprenticeship Program: Level 3 11

12 Learning Task 1 G-2 Self-Test 1 1. What are the two basic types of three-phase systems, and how do they differ from each other? 2. What colour coding does the CEC specify for three-phase AC system conductors? 3. Which conductor would be grounded on a 120 V/208 V, three-phase, four-wire system? 4. Give one reason for choosing a three-phase service over a single-phase service. 5. List three safety considerations for grounding and bonding three-phase systems. Go to the Answer Key at the end of the Learning Guide to check your answers. 12 Construction Electrician Apprenticeship Program: Level 3

13 Learning Task 2: Describe service entrance equipment There are two methods of bringing a three-phase system into a structure: overhead wiring from transformers mounted on poles; or underground wiring from a transformer mounted below or at grade level. The electrician must consider many things when selecting appropriate metering equipment for a polyphase service installation. The booklet Requirements for Secondary Metering Installations from BC Hydro explains how metering arrangements can vary considerably. It is very important to work closely with the Hydro representative during installation. This representative determines such things as system voltages and currents available, and suggests the type of metering equipment required. The location of the service equipment must be as close as practicable to the point where the conductors enter the building. See CEC Rule (1) (e). This essentially means that the conduits, or conductors, on the line side of the service box be on the outside of the building. CEC Rule helps by considering raceways or cables embedded or buried in concrete to be outside. Main service box The service box is an approved assembly that houses the main disconnect and overcurrent protection. Refer to CEC definitions for service box. The main disconnect switch must meet certain general requirements. These are to accommodate: Load demands as derived from applying the CEC rules in CEC Section 8 or 28. Selected fuse size based on the CEC rules in CEC Section 8 or 28. Some of the more common switch sizes available are 100, 200, 400, 600, 800 and 1200 amps. Specially designed switchboards are available in larger ampere ratings. A main breaker may also be chosen instead of a fused disconnect. The advantages of using a breaker are that features such as remote-tripping capabilities and ground-fault protection can be added to the installation. Cost and available fault current capacities are two other considerations when selecting a fuse or breaker for the system. Metering transformer enclosure CEC Rule requires that enclosures for current transformers (CTs) be installed on services exceeding 200 A. (BC Hydro requires CTs over 225 A, or for demands over 50 kw.) The cabinet for housing current and potential transformers (see Figure 1) is supplied by the contractor. The specifications for locating and mounting the case are found in the BC Hydro booklet. Specified minimum enclosure sizes are shown in Table 1. Construction Electrician Apprenticeship Program: LEvel 3 13

14 Learning Task 2 G-2 Table 1: Minimum enclosure sizes (BC Hydro) Enclosed Sizes (L H D) Single-phase service Three-phase service 30" 16.5" 8" up to 600 A up to 400 A & below 300 V 42" 18" 16" 625 A & above 425 A & above Meter cabinet Each three-phase installation requires a metal meter cabinet (see Figure 1). This cabinet is usually supplied by BC Hydro, and a full description of it and its associated equipment can be found in the BC Hydro booklet. Refer also to CEC Rules to Splitter The splitter (see Figure 1) is sized to reflect the loads it serves. It is considered as an extension of the main conductor, and is calculated by using CEC rules from Section 8 or 28. The common sizes available are similar to the main switch sizes. Main switch and metering for three-phase, four-wire systems Figures 1 and 2 represent two of the more common arrangements for service equipment. 14 Construction Electrician Apprenticeship Program: Level 3

15 Learning Task 2 G-2 - Figure 1 Three-phase, four-wire service for a small commercial building Construction Electrician Apprenticeship Program: Level 3 15

16 Learning Task 2 G-2 Figure 1 depicts a 120 V/208 V, three-phase, four-wire system feeding a small commercial building. This is a built-up service composed of a main fused disconnect, metering equipment and auxiliary distribution equipment. The main difference between Figures 1 and 2 is that only one point of metering is required in Figure Figure 2 Three-phase, four-wire service for a small apartment house complex 16 Construction Electrician Apprenticeship Program: Level 3

17 Learning Task 2 G-2 Figure 2 is designed to service a small apartment house or condominium complex. Notice that all of the metering requirements of the building are taken care of at the meter centre. With this arrangement it is also possible to service an individual suite with either 120 V/208 V (two-phase wires and the neutral) or 120 V/208 V, three-phase, four-wire. The use of the four-wire system results in a reduction of wire size, and perhaps, sub-panel size and cost. Grounding and bonding for three-phase, four-wire systems As with any system using a common grounding conductor, you must ground the neutral at the supply and the main service switch. In Figures 1 and 2, the system grounding conductor connects the neutral in the main switch to the grounding electrode. It is sized according to CEC Rule and Table 17; CEC Rule requires that the system grounding conductor must be copper. For example, if 345 A service conductors are used in Figure 1, then CEC Table 17 requires the use of a No. 1/0 AWG copper grounding conductor. Ensure that the neutral is not grounded on the load side of the service disconnect (see CEC Rule ). Also, remove all bonding screws in switches and panelboards. In addition to grounding the system, all non-current-carrying metal parts must be permanently bonded to ensure continuity in the event of a ground fault. This continuity is important because the fault current must flow through the metal parts to ground in order to open the fuse or circuit breaker. The bonding conductor must be of a size that can withstand the level of fault current. For this purpose, the service and distribution equipment is bonded according to CEC Rule and Table 16. In Table 16, the size of the bonding conductor is based on the overcurrent device ahead of the equipment, conduit and so forth. Main switch and metering for three-phase, three-wire delta systems Service entrance equipment for the three-phase, three-wire delta systems looks very much like the equipment for the three-phase, four-wire wye systems. The main difference is that the switch boxes and distribution equipment have terminals for the three live wires but not for a neutral conductor, since there is no neutral conductor available. Conductors and conduit sizes are chosen in the same way as for three-phase, four-wire services (using CEC Sections 8 or 28). Figure 3 illustrates a three-phase, three-wire delta service for a small machine shop. Construction Electrician Apprenticeship Program: Level 3 17

18 Learning Task 2 G Figure 3 Three-phase, three-wire delta service for a small machine shop 18 Construction Electrician Apprenticeship Program: Level 3

19 Learning Task 2 G-2 Grounding and bonding for three-phase, three-wire delta systems Although there is no neutral conductor present in a three-phase, three-wire delta system, the service equipment must still be grounded. The grounding conductor for the service equipment is based on CEC Rule and Table 18. In Figure 3, the steps to determine the size of grounding conductor required are: 1. Use CEC Table 2 to determine the ampacity of the service conductors selected. In this example, the 400 kcmil R90 service conductors have an ampacity of 345 A. 2. Locate the 345A value in CEC Table 18. This specifies a No. 3 AWG conductor for the service ground. Note that this conductor is secured to the main switch cabinet with a lug (see Figure 3). Ground-detection device (CEC Rule ) Whenever a three-phase, ungrounded service is installed, you must install a ground-detection device to indicate the presence of a ground fault (see Figure 4). Ground detector A B C Figure 4 Ground detection device The ground detector has lamps connected between each line and ground. These may be mounted in a compact case or directly on the main switchgear assembly. It works as follows: When no line is grounded, all the lamps glow. If a ground occurs, the lamp connected to the grounded line dims (or goes dark); the other two lamps glow brighter. Metering transformers (CTs and PTs) If current or potential transformers are required for a three-phase service, double-check their installation. Note that the polarity dot for CTs is oriented toward the line side (see Figure 5). Note also that: PTs, CTs and connectors are supplied by BC Hydro. If load and line are reversed, you must reverse the CTs so that the polarity marks are always on the line side. Construction Electrician Apprenticeship Program: Level 3 19

20 Learning Task 2 G-2 The customer must supply and install an insulated block to help connect the potential wire for metering in the instrument transformer enclosure. The neutral conductor must be run into the instrument transformer enclosure. You must insulate the neutral block from the enclosure. Do not bond it. Where parallel conductors are used for greater ampacity, you need connect only one neutral conductor to the insulated neutral block. - - Figure 5 CTs and PTs for three-phase service Now do Self-Test 2 and check your answers. 20 Construction Electrician Apprenticeship Program: Level 3

21 Learning Task 2 G-2 Self-Test 2 1. What is the minimum size of grounding conductor required for a 600 A, three-phase, threewire service? 2. Who determines whether a kwh meter may be placed before or after a switch feeding a subservice? 3. List six common switch sizes that are used for the main service switch. Go to the Answer Key at the end of the Learning Guide to check your answers. Construction Electrician Apprenticeship Program: Level 3 21

22 Answer Key G-2 Answer Key Self-Test 1 1. Wye and delta systems The wye system provides two voltages and has a common circuit conductor, which is always grounded. The delta system usually develops one voltage only and is ungrounded. 2. Phase A = red; Phase B = black; Phase C = blue; and where the neutral is required, neutral = white or natural grey CEC Rule (3) 3. identified neutral conductor CEC Rule (1) (c) 4. Copper savings and economy of equipment 5. Any three of: To protect life from the danger of electric shock, and property from damage by bonding to ground non-current-carrying metal systems. To limit the voltage upon a circuit when exposed to higher voltages than that for which the circuit is designed. In general, to limit AC circuit voltages-to-ground to 150 V or less on circuits supplying interior wiring systems. To facilitate the operation of electrical apparatus and systems. To limit the voltage on a circuit that otherwise occurs through exposure to lightning. Self-Test 2 1. AWG No. 1 copper wire (CEC Table 18) 2. BC Hydro A, 200 A, 400 A, 600 A, 800 A, 1200 A 22 Construction Electrician Apprenticeship Program: Level 3

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