Guide to the IET Wiring Regulations: IET Wiring Regulations (BS 7671:2008 incorporating Amendment No 1:2011) 17th Edition

272 Pages·2013·16.32 MB·English

Guide to the IET Wiring Regulations
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Guide to the IET Wiring Regulations
17th 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
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This edition fi rst published 2012
© 2012 John Wiley & Sons, Ltd
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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
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Contents
Foreword by Giuliano Digilio xi
Preface xiii
Acknowledgements 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
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Contents
C 3 Load assessment 23
C 3.1 Principles and defi nitions 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 fi nal circuit designs 64
C 9.1 Introduction and scope 64
C 9.2 Standard domestic circuits 72
C 9.3 All purpose standard fi nal 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 fi nal circuits 75
C 11.1 Introduction 75
C 11.2 Ring fi nal circuits 75
C 11.3 Radial fi nal circuits 77
Chapter D – Selection and Erection – Equipment 79
D 1 Introduction and fundamentals 79
D 2 Compliance with Standards 80
D 3 Identifi cation of conductors – introduction 81
D 3.1 Principle of required identifi cation (Regulation 514.3.1) 81
D 3.2 Identifi cation by colour 83
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Contents
D 3.3 Identifi cation by marking 85
D 3.4 Alterations and additions – identifi cation 85
D 3.5 Interface marking 85
D 3.6 DC identifi cation 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
infl uences 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 fi re 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 Classifi cation of break times 127
D 15.3 Safety sources 127
D 15.4 Circuits for safety services 127
D 16 Ingress protection (IP), external infl uences 129
D 16.1 General 129
D 16.2 Equipment applications and examples 131
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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 mm2 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 Certifi cation (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 Verifi cation of voltage drop 182
F 4 Certifi cation paperwork 183
F 4.1 Introduction, various certifi cates and schedules 183
F 4.2 Overview of certifi cates and schedules 184
F 4.3 Completing the paperwork 184
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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
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Contents
Appendix 3 – Limiting earth fault loop impedance tables from BS 7671:2008 252
Appendix 4 – Cable data resistance, impedance and ‘R + R ’ values 254
1 2
Appendix 5 – Fuse I2t characteristics 258
Index 259
x
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Foreword by Giuliano Digilio
Head of Technical Services, Electrical Contractors’ Association (E CA)
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 fi rst electrical installation within the UK.
The ECA is fully committed to the development of standards for the national BS 7671 commit-
tee as well as corresponding work in both the European Committee for Electrotechnical Stand-
ardisation (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
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