Guide to the IET Wiring Regulations
Guide to the IET Wiring Regulations 17 th Edition IET Wiring Regulations (BS 7671:2008 incorporating Amendment No. 1:2011) Electrical Contractors Association Extracts from BS 7671:2008 Amd No. 1:2011 have been kindly provided by the Institution of Engineering and Technology (IET) and extracts from other standards have been reproduced with permission from British Standards Institution (BSI). Information and copies of standards are available from BSI at http://shop.bsigroup.com. A John Wiley & Sons, Ltd., Publication
This edition first published 2012 2012 John Wiley & Sons, Ltd Registered office John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, United Kingdom For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at www.wiley.com. The right of the author to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold on the understanding that the publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional should be sought. Library of Congress Cataloging-in-Publication Data Guide to the IET wiring regulations : 17th edition IET wiring regulations (BS 7671:2008 incorporating Amendment no. 1:2011) / Electrical Contractors Association. p. cm. Includes bibliographical references and index. ISBN 978-1-119-96514-5 (pbk.) 1. Electric wiring Insurance requirements Handbooks, manuals, etc. 2. Electric wiring, Interior Handbooks, manuals, etc. I. Electrical Contractors Association (Great Britain) TK3275.G85 2012 621.319'24 dc23 2011047222 A catalogue record for this book is available from the British Library. Paper ISBN: 9781119965145 Set in 10 on 12 pt Sabon by Toppan Best-set Premedia Limited
Contents Foreword by Giuliano Digilio Preface Acknowledgements xi xiii xv Chapter A BS 7671:2008 Amd No. 1:2011 Requirements for Electrical Installations Introduction and Overview 1 A 1 Introduction to BS 7671:2008 1 A 2 Plan and layout of BS 7671:2008 2 A 3 Overview of major changes 5 A 4 Amendment No. 1:2011 9 Chapter B Legal Relationship and General Requirements of BS 7671:2008 Amd No. 1:2011 11 B 1 Legal requirements and relationship 11 B 1.1 Key legal UK legislation 11 B 1.2 The Electricity at Work Regulations 1989 (EWR 1989) 12 B 1.3 The Electricity Safety, Quality and Continuity Regulations 2002 (as amended) 13 B 1.4 The Electricity Act 1984 (as amended) 14 B 1.5 The Building Act 1984, The Building Regulations and Part P 14 B 1.6 The Electromagnetic Compatibility Regulations 2006 15 B 1.7 Tort and negligence 15 B 2 The role of Standards 17 B 3 Part 3 of BS 7671:2008 assessment of general characteristics 18 Chapter C Circuitry and Related Parts of BS 7671:2008 Amd No. 1:2011 21 C 1 Introduction 21 C 2 Design procedure overview 21 v
Contents C 3 Load assessment 23 C 3.1 Principles and definitions 23 C 3.2 Maximum demand assessment 24 C 3.3 Diversity 25 C 4 Circuitry design 26 C 4.1 Introduction 26 C 4.2 Protection against overcurrent in general 28 C 4.3 Overload protection 28 C 4.4 Fault protection 40 C 4.5 Voltage drop 44 C 4.6 Disconnection and electric shock protection 49 C 5 Sub-mains 56 C 5.1 Diversity 56 C 5.2 Distribution circuit (sub-main) selection 57 C 5.3 Armouring as a CPC 57 C 5.4 Automatic disconnection for sub-mains 58 C 6 Discrimination co-ordination 58 C 6.1 Principles and system co-ordination 58 C 6.2 Fuse-to-fuse discrimination 59 C 6.3 Circuit breaker to circuit breaker discrimination 60 C 6.4 Circuit breaker to fuse discrimination 62 C 7 Parallel cables 62 C 7.1 General and BS 7671 requirements 62 C 7.2 Unequal current sharing 63 C 8 Harmonics 63 C 8.1 Requirements 63 C 8.2 Harmonic assessment 63 C 9 Standard final circuit designs 64 C 9.1 Introduction and scope 64 C 9.2 Standard domestic circuits 72 C 9.3 All purpose standard final circuits 73 C 10 RCDs and circuitry 73 C 10.1 Introduction increased use of RCDs 73 C 10.2 Consumer unit arrangements for RCDs 74 C 11 Ring and radial final circuits 75 C 11.1 Introduction 75 C 11.2 Ring final circuits 75 C 11.3 Radial final circuits 77 Chapter D Selection and Erection Equipment 79 D 1 Introduction and fundamentals 79 D 2 Compliance with Standards 80 D 3 Identification of conductors introduction 81 D 3.1 Principle of required identification (Regulation 514.3.1) 81 D 3.2 Identification by colour 83 vi
Contents D 3.3 Identification by marking 85 D 3.4 Alterations and additions identification 85 D 3.5 Interface marking 85 D 3.6 DC identification 86 D 4 Protection against voltage and electromagnetic disturbance 86 D 4.1 General 86 D 4.2 Electromagnetic compatibility and prevention of mutual detrimental influences 88 D 5 Wiring systems 95 D 5.1 The choice of wiring systems 95 D 5.2 Circulating currents and eddy currents in single-core installations 98 D 5.3 Electrical connections and joints 100 D 5.4 Wiring systems minimizing spread of fire 104 D 5.5 Proximity to other services 106 D 6 Circuit breakers 106 D 6.1 General 106 D 6.2 Operation and characteristics 107 D 6.3 Ambient temperature de-rating 110 D 7 Residual current devices 111 D 7.1 BS 7671 applications 111 D 7.2 Operation and BS 7671 requirements 112 D 7.3 Unwanted RCD tripping and discrimination 113 D 7.4 d.c. issues for RCDs 115 D 7.5 TT installations and RCDs 115 D 8 Other equipment 116 D 8.1 Isolation and switching 116 D 8.2 Consumer units for domestic installations 116 D 8.3 Overvoltage, undervoltage and electromagnetic disturbances 116 D 8.4 Surge protective devices 118 D 8.5 Insulation monitoring devices (IMDs) 118 D 8.6 Residual current monitors (RCMs) 119 D 9 Generating sets 121 D 10 Rotating machines 121 D 11 Plugs and socket-outlets 122 D 12 Electrode water heaters and electrode boilers 123 D 13 Heating conductors 124 D 14 Lighting and luminaires 124 D 15 Safety services 127 D 15.1 Introduction 127 D 15.2 Classification of break times 127 D 15.3 Safety sources 127 D 15.4 Circuits for safety services 127 D 16 Ingress protection (IP), external influences 129 D 16.1 General 129 D 16.2 Equipment applications and examples 131 vii
Contents Chapter E Earthing and Bonding 133 E 1 Introduction 133 E 2 Earthing arrangements 133 E 3 General requirements of earthing and bonding 138 E 4 Protective conductors 139 E 4.1 General 139 E 4.2 Physical types of protective conductor 140 E 4.3 Sizing protective conductors 141 E 4.4 Protective conductors up to 16 mm 2 142 E 4.5 The earthing conductor 146 E 5 Armoured cables as protective conductors 147 E 5.1 General 147 E 5.2 ERA Report on current sharing between armouring and CPC 148 E 5.3 ECA advice and recommendations 148 E 6 Protective bonding 149 E 6.1 Purpose of protective equipotential bonding 149 E 6.2 BS 7671 requirements 149 E 6.3 Bonding solutions for the modern installation 149 E 6.4 Sizing main bonding conductors 154 E 6.5 Domestic protective bonding layouts 155 E 6.6 Supplementary equipotential bonding 157 E 7 High earth leakage installations 158 Chapter F Inspection Testing and Certification (Part 6) 161 F 1 Introduction 161 F 1.1 Inspection and testing an integrated procedure 161 F 2 Visual inspection 162 F 3 Testing 164 F 3.1 Introduction pass and fail nature 164 F 3.2 Required tests 164 F 3.3 Continuity testing 165 F 3.4 Ring continuity 168 F 3.5 Insulation resistance testing 171 F 3.6 Polarity testing 174 F 3.7 Earth fault loop impedance (ELI) testing 175 F 3.8 Prospective fault current testing 179 F 3.9 Testing RCDs and other functional tests 181 F 3.10 Verification of voltage drop 182 F 4 Certification paperwork 183 F 4.1 Introduction, various certificates and schedules 183 F 4.2 Overview of certificates and schedules 184 F 4.3 Completing the paperwork 184 viii
Contents Chapter G Special Locations 201 G 1 Introduction purpose and principles 201 G 1.1 Introduction 201 G 1.2 Purpose and principles 201 G 1.3 Particular requirements and numbering 202 G 2 Locations containing a bath or shower (701) 203 G 2.1 Introduction and risks 203 G 2.2 Zone concept 203 G 2.3 Electric shock requirements 204 G 2.4 Equipment selection and erection 207 G 3 Swimming pools and other basins (702) 208 G 3.1 Introduction and risks 208 G 3.2 Zone concept 209 G 3.3 Requirements and guidance 211 G 4 Agricultural and horticultural premises (705) 214 G 4.1 Introduction, purpose and principles 214 G 4.2 Requirements and guidance 214 G 5 Caravan parks and camping parks (708) 218 G 5.1 Introduction purpose and principles 218 G 5.2 Requirements and guidance 218 G 6 Medical locations (710) 222 G 6.1 Introduction and risks 222 G 6.2 Medical groups and class of safety service supply 222 G 6.3 Requirements 223 G 7 Exhibitions, shows and stands (711) 227 G 7.1 Introduction and risks 227 G 7.2 Requirements and guidance 228 G 8 Solar photovoltaic (PV) power supply systems (712) 229 G 8.1 Introduction principles and terminology 229 G 8.2 Requirements 231 G 8.3 Notes and guidance 232 G 9 Mobile or transportable units (717) 235 G 9.1 Scope and application 235 G 9.2 Requirements 235 G 9.3 Notes and guidance 236 G 10 Floor and ceiling heating systems (753) 237 G 10.1 Introduction 237 G 10.2 Requirements 238 G 10.3 Notes and guidance 238 References 240 Appendices 243 Appendix 1 Standards and bibliography 244 Appendix 2 Popular cables: current rating tables from BS 7671:2008 Appendix 4 249 ix
Contents Appendix 3 Limiting earth fault loop impedance tables from BS 7671:2008 252 Appendix 4 Cable data resistance, impedance and R 1 + R 2 values 254 Appendix 5 Fuse I 2 t characteristics 258 Index 259 x
Foreword by Giuliano Digilio Head of Technical Services, Electrical Contractors Association ( ECA) Amendment No. 1:2011 of the IEE Wiring Regulations BS 7671:2008 includes a name change; they are now known as the IET Wiring Regulations BS 7671:2008 Amd No. 1:2011. The IEE Wiring Regulations, and more lately BS 7671, have always been important for electrical contractors and for installation designers, and they are a key factor in the implementation of electrical safety within the UK and indeed overseas. The IEE Wiring Regulations go back to the end of the 19th century, almost to the time of the very first electrical installation within the UK. The ECA is fully committed to the development of standards for the national BS 7671 committee as well as corresponding work in both the European Committee for Electrotechnical Standardisation (CENELEC) and the International Electrotechnical Commission (IEC). This includes a considerable amount of work in the preparation for BS 7671:2008 Amd No. 1:2011. I am pleased that you have purchased the ECA s Guide to the IET Wiring Regulations and I trust that this quality publication will aid to enhance the understanding and knowledge within the electrical industry for both electrical contractors and electrical designers. xi
Preface This guide discusses the requirements of BS 7671:2008 including Amendment No. 1:2011, also known as the IET Wiring Regulations 17th Edition. It has been published by the Electrical Contractors Association to help their members and the contracting industry at large to understand and apply the IET Wiring Regulations. This guide is a valuable resource for all users of BS 7671 including apprentices and electricians who perhaps want to dig a bit deeper into the background of the Regulations, together with electrical technicians, installation engineers and design engineers. Most individuals who have any involvement with BS 7671 will find the book of considerable help and benefit in their everyday work. Steve Mitchell Divisional Director Electrical Contractors Association xiii
Acknowledgements The ECA are very pleased to acknowledge the contribution made to this revision of the guide by Giuliano Digilio, Head of Technical Services and Graeme Wool, Principal Engineer. Paul Cook, former staff member of the IET, is thanked for his assistance with the reviewing and updating work on this publication in line with Amendment No. 1 of BS 7671:2008 Requirements for Electrical Installations. Steve Mitchell Divisional Director Electrical Contractors Association xv