A Practical Guide to the 17Th Edition of the Wiring Regulations
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A Practical Guide to the 17th Edition of the Wiring Regulations This page intentionally left blank A Practical Guide to the 17th Edition of the Wiring Regulations Christopher Kitcher AMSTERDAM • BOSTON • HEIDELBERG • LONDON NEW YORK • OXFORD • PARIS • SAN DIEGO SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Newnes is an imprint of Elsevier Newnes is an imprint of Elsevier The Boulevard, Langford Lane, Oxford OX5, 1GB, UK 30 Corporate Drive, Suite 400, Burlington, MA 01803 First edition 2010 Copyright © 2010, Christopher Kitcher. Published by Elsevier Ltd. All rights reserved The right of Christopher Kitcher to be identified as the author of this work has been asserted in accordance with the Copyright, Design and Patents Act 1988. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress ISBN : 978-0-08-096560-4 For information on all Newnes publications visit our website at www.newnespress.com Typeset by MPS Limited, a Macmillan Company, Chennai, India www.macmillansolutions.com Printed and bound in Italy 1 0 1 1 1 2 1 3 1 4 1 0 9 8 7 6 5 4 3 2 1 Contents Foreword xi Preface xiii BS 7671 Wiring Regulations 2008 1 Part 1 Licensing laws 4 Manufacturer ’ s instructions 4 British Standards 4 Chapter 13 5 Fundamental principles 5 131 Protection for safety 5 131.2.1 Basic protection 6 131.2.2 Fault protection 6 131.1 Protection against thermal effects 6 131.4 Protection against overcurrent 7 131.5 Protection against fault current 7 131.6 Protection against voltage disturbances and measures against electromagnetic disturbances 7 131.7 Protection against power supply interruption 7 131.8 Additions and alterations to an installation 7 132.1 Design 8 132.2 Characteristics of supply 8 132.3 Nature of demand 8 132.4 Electrical supply systems for safety services or standby electrical supply systems 8 132.5 Environmental conditions 8 132.6 Cross-sectional areas of conductors 9 132.7 Types of wiring and method of installation 9 132.8 Protective equipment 9 132.9 Emergency control 9 132.10 Disconnecting devices 9 132.11 Prevention of mutual detrimental infl uence 10 132.12 Accessibility of electrical equipment 10 132.13 Documentation for the electrical installation 10 132.14 Protective devices and switches 10 132.15 Isolation and switching 10 133 Selection of electrical equipment 11 134 Erection and verifi cation of electrical installations 11 134.1 Erection 11 134.2 Initial verifi cation 11 135 Periodic inspecting and testing 11 v vi Contents Part 2 Defi nitions 13 TT system 13 TN -S system 15 TN -C-S system 15 Part 3 301 Assessment of general characteristics 19 Chapter 31 19 311 Maximum demand and diversity 19 312 Arrangement of live conductors and type of earthing 22 313 Supplies 22 314 Division of installation 24 Chapter 32 24 Classifi cation of external infl uences 24 Chapter 33 25 331.1 Compatibility 25 332 Electromagnetic capability 25 Chapter 34 25 341 Maintainability 25 Chapter 35 25 351 Safety services 25 Chapter 36 26 361 Continuity of service 26 Part 4 Chapter 41 27 Protection against electric shock 27 411.7 Functional extra low voltage 36 411.8 Reduced low-voltage systems 37 412 Double or reinforced insulation 39 413 Electrical separation 39 417 Obstacles and placing out of reach 40 418 40 418.1 Non-conducting locations 40 418.2 Protection by earth-free local equipotential bonding 41 Chapter 42 41 Protection against thermal effects 41 Protection against fi re caused by electrical equipment (421) and locations with risks of fi re due to the nature of processed or stored materials (422) 42 Chapter 43 46 Protection against overcurrent 46 433.2 Position of devices for protection against overload 54 433.3.1 Omission of devices for protection against overload 55 433.4 Conductors in parallel 57 434.5 Characteristics of a fault current protective device 59 435.2 Protection offered by separate devices 61 Chapter 44 61 Protection against voltage disturbances and electromagnetic disturbances 61 442 61 443 61 445 Protection against undervoltages 62 Contents vii Part 5 Selection and erection of equipment 63 Chapter 51 63 512 Operational conditions and external infl uences 63 513 Accessibility 65 514 Identifi cation and notices 65 515 Prevention of mutual detrimental infl uence 70 Chapter 52 70 Selection and erection of wiring systems 70 521 Types of wiring system 70 521.5 Electromechanical effects in a.c. circuits 71 522 Selection and erection of wiring systems in relation to external infl uences 72 523 Current carrying capacity of cables 75 526 Electrical connections 78 527 Selection and erection of wiring systems to minimise the spread of fi re 79 527.2 Sealing of wiring system penetrations 79 528 Proximity of wiring systems to other services 79 528.2 Proximity of communication cables 80 528.3 Proximity to non-electrical services 80 529 Selection and erection of wiring systems in relation to maintainability 80 Chapter 53 80 Protection, isolation, switching, control and monitoring 80 538 Monitoring 86 Chapter 54 87 Earthing arrangements and protective conductors 87 542.1.8 Separate installations sharing the same supply 89 542.2 Earth electrodes 92 543.7 Earthing requirements for the installation of equipment having high protective conductor currents 102 544 Protective bonding conductors 105 544.2 Supplementary bonding conductors 105 Chapter 55 106 Other equipment 106 551 Low-voltage generating sets 106 551.6 Additional requirements where the generator is used as a standby system 107 552 Rotating machines 107 554.2 Heaters having immersed elements 107 554.4 Heating conductors and cables 108 559.4 General requirements for outdoor lighting installations 108 559.6.1.5 Fixing of the luminaires 108 559.6.2.2 Through wiring 109 559.10.3.1 Outdoor lighting installations, highway power supplies and street furniture 110 Chapter 56 110 Safety services 110 Part 6 Inspection and testing 113 Chapter 61 114 Initial verifi cation 114 Sequence of tests 123 Protection by SELV, PELV or electrical separation 127 SELV 127 viii Contents PELV 127 Electrical separation 127 Polarity 127 Earth fault loop impedance 128 Ze , external earth loop impedance 128 Zs , circuit earth fault loop impedance 129 Prospective fault current 130 Check of phase rotation 131 Functional testing 132 Periodic inspection and testing 133 Shower circuit 146 Cooker circuit 146 Socket outlet 146 Immersion heater circuits 147 Lighting circuits 147 Three-phase circuits/systems 148 Periodic testing 148 Part 7 Special installations or locations 155 Section 701 155 Locations containing a bath or shower 155 Zone 0 160 Zone 1 160 Zone 2 161 Section 702 162 Swimming pools and other basins 162 Section 703 163 Rooms and cabins containing sauna heaters 163 Section 704 165 Construction and demolition sites 165 Section 705 166 Agricultural and horticultural premises 166 Section 706 168 Conducting locations with restrictive movement 168 Section 708 169 Electrical installations in caravan and camping parks 169 Section 709 171 Marinas and similar locations 171 Section 711 172 Exhibitions, shows and stands 172 Section 712 173 Solar PV power supply systems 173 Section 717 185 Mobile or transportable units 185 Section 721 187 Electrical installations in caravans and motor caravans 187 Section 740 188 Temporary electrical installations for structures, amusement devices and booths at fairgrounds, amusement parks and circuses 188 Section 753 188 Floor and ceiling heating systems 188 Contents ix Appendices Appendix 1 191 Appendix 2 191 Appendix 3 191 Appendix 4 194 Ambient temperature 194 Grouping 195 Thermal insulation 197 Voltage drop 199 Voltage drop in ring circuits 200 Cable calculation 202 Appendix 5 205 Classifi cation of external infl uences 206 Appendix 6 206 Appendix 7 206 Harmonised cable core colours 207 Appendix 8 207 Current carrying capacity and voltage drop for bus bar