18th Edition IET Wiring Regulations Electric Wiring for Domestic Installers This book is essential reading for anyone studying towards Domes- tic Installer status with an approval body such as NICEIC, NAPIT or ELECSA, in line with Part P of the Building Regulations, and also serves as a handy pocket guide to best practice for electricians. Although not intended as a DIY manual, non-qualified persons will also find it useful reading. � ��� The how-to guide for home wiring to professional standards. � ��� �Now with more on LED lighting. � ��� �Essential reading for serious DIY, electrical installation, basic plumbing, heating systems, TV and security alarm installation � ��� Up to date with the 18th Edition of the IET Wiring Regulations. Brian Scaddan, I Eng, MIET, is an Honorary Member of City & Guilds and has over 45 years’ experience in further education and training. He was Director of Brian Scaddan Associates Ltd, an approved training centre offering courses on all aspects of electrical installation contracting, includ- ing those for City & Guilds and EAL. He is also a leading author of books on other installation topics. By the same author 18th Edition IET Wiring Regulations: Design and Verification of Electrical Installations, 9th ed, 978-1-138-60600-5 18th Edition IET Wiring Regulations: Explained and Illustrated, 11th ed, 978-1-138-60605-0 18th Edition IET Wiring Regulations: Inspection, Testing and Certification, 9th ed, 978-1-138-60607-4 18th Edition IET Wiring Regulations: Wiring Systems and Fault Finding for Installation Electricians, 7th ed, 978-1-138-60609-8 Electrical Installation Work, 8th ed, 978-1-138-84927-3 PAT: Portable Appliance Testing, 4th ed, 978-1-138-84929-7 The Dictionary of Electrical Installation Work, 978-0-08-096937-4 18th Edition IET Wiring Regulations Electric Wiring for Domestic Installers 16th Edition Brian Scaddan Sixteenth edition published 2019 by Routledge 2 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN and by Routledge Routledge is an imprint of the Taylor & Francis Group, an informa business © 2019 Brian Scaddan The right of Brian Scaddan to be identified as author of this work has been asserted by him in accordance with sections 77 and 78 of the Copyright, Designs and Patents Act 1988. All rights reserved. No part of this book may be reprinted or reproduced or utilised in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers. Trademark notice: Product or corporate names may be trademarks or registered trade- marks, and are used only for identification and explanation without intent to infringe. First edition published 1940 by Newnes, an imprint of Elsevier Fifteenth edition published by Routledge 2015 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 has been requested for this book ISBN: 978-1-138-60604-3 (hbk) ISBN: 978-1-138-60602-9 (pbk) ISBN: 978-0-429-46691-5 (ebk) Typeset in Kuenstler 480 and Trade Gothic by Servis Filmsetting Ltd, Stockport, Cheshire 52 Vanderbilt Avenue, New York, NY 10017 v Contents PREFACE ......................................................................................................... vii CHAPTER 1 The UK Generation, Transmission and Distribution System .............1 Voltage Bands ....................................................................................................2 The Electricity Safety, Quality and Continuity Regulations 2002 (ESQCR) .............5 The Electricity at Work Regulations 1989 ............................................................5 The IET Wiring Regulations (BS 7671) ................................................................5 The Building Regulations 2010 Part ‘P’ ..............................................................6 Earthing Systems ...............................................................................................7 CHAPTER 2 Domestic Electrical Installations ...................................................11 The Main Intake Position ..................................................................................11 Circuits ............................................................................................................17 Cables .............................................................................................................30 Wiring Systems and Installation Methods ..........................................................34 CHAPTER 3 The Importance of Earthing and Bonding .....................................49 Electric Shock ..................................................................................................49 Basic Protection ...............................................................................................51 Fault Protection ................................................................................................51 What is Earth and Why and How Do We Connect to It? ......................................52 Residual Current Devices .................................................................................59 Bonding: Questions and Answers .....................................................................61 The Faraday Cage ............................................................................................62 CHAPTER 4 Bathrooms ...................................................................................63 Zone 0 .............................................................................................................63 Zone 1 .............................................................................................................64 Zone 2 .............................................................................................................65 Supplementary Equipotential Bonding ..............................................................66 CHAPTER 5 Protection ....................................................................................67 Protection Against Mechanical Damage ............................................................68 Protection of Persons/Livestock Against Dangers ..............................................70 Contents vi CHAPTER 6 Circuit Design ..............................................................................79 Diversity ...........................................................................................................80 Basic Circuit Design .........................................................................................82 Summary .........................................................................................................93 CHAPTER 7 Inspection and Testing .................................................................95 Instruments .....................................................................................................95 Testing ...........................................................................................................101 CHAPTER 8 Security Alarm and Telephone Systems ......................................121 Security Alarms ..............................................................................................121 Telephone Systems ........................................................................................123 APPENDIX 1 Basic Electrical Theory Revision ................................................127 Electrical Quantities and Units ........................................................................127 Power, Current and Voltage ............................................................................131 APPENDIX 2 Conductor Identification, Notices and Warning Labels ...............133 Conductor Identification .................................................................................133 Notices and Warning Labels ...........................................................................134 INDEX ..........................................................................................................135 vii Preface This book is a guide to the practical aspects of domestic electric wiring. It seeks to address the areas of most concern to the qualified electri- cian, especially design and testing. It will also be a useful addition to the resources available for students working towards NVQs or City & Guilds and EAL qualifications. It is also a vital reference source for many other professionals and opera- tives whose work demands a knowledge of electrical installations, includ- ing electrical engineers, heating engineers, architects and maintenance staff. The contents will be of value to those intending to gain a Domestic Installer Scheme Qualification which relates to Part ‘P’ of the Building Regulations. It is not intended as a DIY manual, although some non-qual- ified persons may find certain topics useful before calling in qualified operatives. The contents of this new edition cover current professional best practice and are fully compliant with the 18th Edition IET Wiring Regulations. Brian Scaddan CHAPTER 2 18th Edition IET Wiring Regulations: Electric Wiring for Domestic Installers. 978-1-138-60604-3. © Brian Scaddan. Published by Taylor & Francis. All rights reserved. 1 The UK Generation, Transmission and Distribution System Important terms/topics covered in this chapter: � �� Voltage bands � �� The Electricity Safety Quality and Continuity Regulations (ESQCR) � �� BS 7671: 2018 The Wiring Regulations � �� The Electricity at Work Regulations (EAWR) � �� The Building Regulations � �� TT, TN-S and TN-C-S earthing systems By the end of this chapter the reader should: � �� �know the regulations and recommendations relating to electrical installations, � �� �be aware of the Building Regulations relevant to electrical installa- tions in dwellings, � �� �be aware of the notifiable work under Part ‘P’ of the Building Regulations, � �� understand the arrangements of the UK earthing systems. In the early days of electricity supply, each town or city in the United Kingdom had its own power station which supplied the needs of its particular area. Standardization was not evident and many different voltages and frequencies were used throughout the country. By the time of the First World War (1914–1918), there were some 600 independent power stations in use. However, the heavy demands made by the war indus- try showed the inadequacies of the system and several select commit- tees were set up to investigate possible changes. Little was achieved until 1926, when it was suggested that 126 of the largest and most efficient power stations should be selected and connected by a grid of high-voltage CHAPTER 1 The UK Generation, Transmission and Distribution System 2 transmission lines covering the whole country, and, at the same time, the frequency standardized at 50 Hz. The remaining power stations would be closed down and local supply authorities would obtain their electricity in bulk from the grid, via suitable substations. The system voltage was 132 000 V (132 kV) and the supply frequency 50 Hz. On 1 April 1948, the whole of the electricity supply industry was nation- alized and, in 1957, the ‘Central Authority’ responsible for the genera- tion of electricity was renamed the ‘Central Electricity Generating Board’ (CEGB). Since then, of course, the electricity industry has become privatized and the CEGB has been replaced by the National Grid Company, which buys, at the lowest price, generated electricity from such companies as National Power, PowerGen, Nuclear Electric, French Electrique and Scot- tish Hydro Electric. Electricity boards have become Distribution Network Operators (DNOs) and they, in turn, buy electrical energy from the National Grid Company to distribute to their own consumers. The broad structure of the industry is shown in Figure 1.1. VOLTAGE BANDS The very nature of the grid system is such that power has to be transmit- ted over large distances. This immediately creates a problem of voltage drop. To overcome this problem, a high voltage is used for transmission (400 or 132 kV), the 400 kV system being known as the ‘Super Grid’. We cannot, however, generate at such high voltages (the maximum in modern generators is 25 kV) and transformers are used to step up the generated voltage to the transmission voltage. At the end of a transmission line is a grid substation, where the requirements of the grid system in that area can be controlled and where the transmission voltage is stepped down via a transformer to 132 kV. It is at this stage that the different DNOs distribute the power required by their consumers around that particular area. The system voltage is then further reduced at substations to 33 000, 11 000 and 415/240 V (Figure 1.2). The UK Generation, Transmission and Distribution System 3 The declared voltage at consumers’ terminals is now 400 V three- phase/230 V single-phase +10 to 6%. However, the measured voltage is still likely to be 415/240 V for many years. The Wiring Regulations BS 7671:2008 indicate two voltage bands, as follows: Voltage band 1: Extra Low Voltage (ELV) which does not exceed 50 Vac. In domestic installations ELV is used for bell and call systems,12 V lighting (incorrectly called low voltage lighting by manufacturers) and for some circuits in bath/shower rooms, where it is Separated Extra Low Voltage (SELV). See also Chapter 4 Bathrooms. Voltage band 2: Low voltage (LV) which exceeds ELV (50 Vac) but does not exceed 1000 Vac. These circuits cover the normal domestic circuits for power and lighting. FIGURE 1.1 PowerGen National Power Nuelear Eleetrie, ete. National Grid Company The distribution network operators Industrial, eommereial and domestie eonsumers GENERATION TRANSMISSION DISTRIBUTION FIGURE 1.2 The UK electrical energy system. Generating companies: Super Grid National Power National Grid Co. PowerGen Nuclear Electric French Electrique Scottish Hydro Electric Generation, transmission and distribution 01 electricity Electricity Boards Heavy industry 33000V Light industry 11000V Towns 230 V Transformer 11 000/230 V A B C and 400/230 V 132000 V 400000 V Gridsystem Transformer 400 0001132 000 V Translormer 132 000/33 000 V villages 11000V Transformer 33000/11 000 V 11000V Transformer 11 000/400/230 V Farms The UK Generation, Transmission and Distribution System 5 THE ELECTRICITY SAFETY, QUALITY AND CONTINUITY REGULATIONS 2002 (ESQCR) Clearly, from the public’s point of view, there must be safeguards from the dangers that electricity supply systems may create and also guarantees that, other than in exceptional circumstances, a constant supply will be maintained. Such safeguards and guarantees are embedded in the Electricity Safety, Quality and Continuity Regulations 2002. With regard to a consumer installation, the regulations advise the supplier (usually the DNO) to provide a service cable, protective device and any wiring up to the consumer ’s supply terminals. They also require the supplier to give written details of external loop impedance and prospective short-circuit values. The regulations also permit the supplier to withhold or discontinue a sup- ply if it is considered that the consumer’s installation is not safe or could interfere with the public supply. THE ELECTRICITY AT WORK REGULATIONS 1989 These regulations come under the umbrella of the Health and Safety at Work Act 1974 and supersede the Factories Act (Special Regulations) 1908 and 1944. They affect every person at work, whether an employer, an employee or a self-employed person, and they place a duty on each per- son to carry out safe working practices with regard to matters (electrical) that are within his or her control. This piece of legislation is the only one in the United Kingdom that assumes anyone who contravenes certain regulations to be guilty. Such a person then has to demonstrate that he or she took all reasonable steps to prevent danger in order to prove his or her innocence and avoid prosecution. THE IET WIRING REGULATIONS (BS 7671) These regulations, although having British Standard status, are non- statutory. However, they may be used in a court of law to claim compliance The UK Generation, Transmission and Distribution System 6 with statutory regulations such as the Electricity at Work Regulations 1989. They are, basically, a set of recommendations dealing with the safe design, construction, inspection and testing of low-voltage installations. There is no point at this stage in expanding further on these regulations, as they will be referred to throughout the remaining chapters. THE BUILDING REGULATIONS 2010 PART ‘P’ The following material is taken from The Building Regulations 2000 approved document P. © Crown Copyright material is reproduced with the permission of the controller of HMSO and Queen’s Printer for Scotland. Part ‘P’ Part ‘P’ of the Building Regulations requires that installations in dwellings be designed, installed and inspected and tested to the requirements of the current edition of the IET Wiring Regulations, BS 7671. Details of some such work need to be notified to the Local Building Con- trol Authority (LABC). This is a legal requirement. Notifiable work � �� Any new circuit fed from the consumer unit � �� Replacement of a consumer unit � �� �Any work, additions or alterations in a bath/shower room, sauna or swimming pool. Non-notifiable work Any other work that involves replacements, additions or alterations any- where else including gardens. Certification All electrical work has to be inspected, tested and certified with the issue of either: