A Practical Guide to the Wiring Regulations (2009): 17th Edition IEE Wiring Regulations (BS 7671:2008), 4th Edition

643 Pages·2008·8.16 MB·English

A Practical Guide to the
Wiring Regulations: 17th
Edition IEE Wiring
Regulations (BS 7671:2008)
Eur Ing Geoffrey Stokes
Eur Ing John Bradley
WILEY
A PRACTICAL GUIDE
TO THE WIRING
REGULATIONS
A PRACTICAL GUIDE
TO THE WIRING
REGULATIONS
th
17 EDITION IEE WIRING
REGULATIONS (BS 7671:2008)
Fourth Edition
Eur Ing Geoffrey Stokes
BSc (Hons), CEng, FIEE, FCIBSE
Eur Ing John Bradley
BSc, CEng, MIEE, FCIBSE
A John Wiley and Sons, Ltd., Publication
 Geoffrey Stokes 1994, 1999, 2002
 Geoffrey Stokes and John Bradley 2009
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First edition published 1994
Second edition published 1999
Third edition published 2002
Fourth edition published 2009
Library of Congress Cataloging-in-Publication Data
Stokes, Geoffrey, CEng.
A practical guide to the wiring regulations/Geoffrey Stokes. – 4th ed.
p.cm.
Includes bibliographical references and index.
ISBN 978-1-4051-7701-6 (cloth)
1. Electric wiring–Insurance requirements–Handbooks, manuals, etc. 2. Electric wiring, Interior–Handbooks,
manuals, etc. 3. Electric apparatus and appliances–Installation–Great Britain–Handbooks, manuals, etc.
I. Bradley, John. II. Title.
TK3275.S86 2008
621.319’24021841–dc22
2008047084
A catalogue record for this book is available from the British Library
ISBN 978-1-4051-7701-6
Typeset in 10/12 Times by Laserwords Private Limited, Chennai, India
Printed and bound in Great Britain by TJ International, Padstow, Cornwall
For further information on Blackwell Science, visit our website: www.blackwell-science.com
Contents
About the authors xvii
Preface to the Fourth Edition xix
Acknowledgements xxi
Notation xxiii
1 Plan and terminology of BS 7671:2008 and supporting publications 1
1.1 Plan of BS 7671:2008 1
1.2 Terminology of BS 7671:2008 5
1.3 Supporting publications 6
2 Electricity, the law, standards and codes of practice 7
2.1 General 7
2.2 Electricity: the hazards 7
2.3 The law 12
2.3.1 Electricity Safety, Quality and Continuity Regulations 2002 12
2.3.2 The Electricity at Work Regulations 1989 (EWR) 12
2.4 Standards and codes of practice 13
2.4.1 The IEE Wiring Regulations: BS 7671 13
2.4.2 Electric signs and high-voltage luminous-discharge-tube installations:
BS 559 and BS EN 50107 13
2.4.3 Emergency lighting: BS 5266 13
2.4.4 Electrical equipment for explosive gas atmospheres: BS EN 60079 13
2.4.5 Electrical equipment for use in the presence of combustible dust:
BS EN 50281 and BS EN 61241 13
2.4.6 Electrical installations in opencast mines and quarries: BS 6907 13
2.4.7 Fire detection and alarm systems for buildings: BS 5839 14
2.4.8 Telecommunications systems: BS 6701 14
2.4.9 Electric surface heating: BS 6351 14
2.4.10 Lightning protection: BS EN 62305 14
2.4.11 Lift installations: BS 5655 and BS EN 81-1 15
vi Contents
2.4.12 Equipment 15
3 Scope, object and fundamental principles 17
3.1 General 17
3.2 Scope 17
3.2.1 General 17
3.2.2 Exclusions from the scope 19
3.2.3 Equipment 20
3.2.4 Relationship with statutory authorities 20
3.2.5 Installations in premises subjected to licensing 20
3.3 Object and effects 20
3.3.1 General 20
3.3.2 New materials and inventions 21
3.4 Fundamental principles 21
3.4.1 General 21
3.4.2 Electric shock: basic protection 22
3.4.3 Electric shock: fault protection 23
3.4.4 Protection against thermal effects 23
3.4.5 Protection against overcurrent 23
3.4.6 Protection against fault current 24
3.4.7 Protection against voltage disturbances and measures against
electromagnetic influences 24
3.4.8 Protection against supply interruption 24
3.4.9 Additions and alterations to an installation 26
3.4.10 Design 26
3.4.11 Selection of electrical equipment 26
3.4.12 Erection, initial verification of electrical installations, and periodic
inspection and testing 26
4 Assessment of general characteristics 29
4.1 General 29
4.2 Loading, maximum demand and diversity 29
4.2.1 General 29
4.2.2 Lighting: loading and diversity 30
4.2.3 Heating: loading and diversity 32
4.2.4 Cookers: loading and diversity 32
4.2.5 Water heaters: loading and diversity 33
4.2.6 Motors: loading and diversity 33
4.2.7 Stationary equipment: loading and diversity 34
4.2.8 Conventional circuits: loading and diversity 34
4.2.9 Socket-outlet circuits other than conventional circuits: loading and
diversity 34
4.3 Arrangement of live conductors and type of earthing 35
4.3.1 Arrangement of live conductors 35
4.3.2 Type of earthing 35
Contents vii
4.4 Nature of supply 40
4.4.1 General 40
4.4.2 Voltage 40
4.4.3 The nature of current and frequency 41
4.4.4 Prospective short-circuit current 41
4.4.5 External earth fault loop impedance 42
4.4.6 Suitability of supply 43
4.4.7 Type and rating of overcurrent device at the origin 44
4.5 Supplies for safety services and standby purposes 44
4.6 Installation circuit arrangements 44
4.7 External influences 45
4.8 Compatibility 45
4.9 Maintainability 46
5 Protection against electric shock 47
5.1 General 47
5.2 Provisions for basic protection 51
5.2.1 General 51
5.2.2 Basic insulation of live parts 52
5.2.3 Barriers or enclosures 52
5.3 Protective measure: automatic disconnection of supply 53
5.3.1 General 53
5.3.2 Basic protection in ADS 54
5.3.3 General requirements for fault protection in ADS 54
5.3.4 Fault protection in ADS: for TN systems 60
5.3.5 Fault protection in ADS: for TT systems 67
5.3.6 Fault protection in ADS: for IT systems 69
5.3.7 Functional extra-low voltage 71
5.3.8 Reduced low-voltage systems 72
5.4 Protective measure: double or reinforced insulation 75
5.5 Protective measure: electrical separation 77
5.6 Protective measure: extra-low voltage provided by SELV or PELV 78
5.7 Additional protection 81
5.8 Obstacles and placing out of reach 82
5.8.1 Obstacles 82
5.8.2 Protection by placing out of reach 82
5.9 Protective measures for application only where the installation
is controlled or under the supervision of skilled or instructed persons 83
5.9.1 Non-conducting location 83
5.9.2 Protection by earth-free local equipotential bonding 85
5.9.3 Electrical separation for the supply to more than one item of
current-using equipment 86
6 Protection against thermal effects 89
6.1 General 89
viii Contents
6.2 Fire caused by electrical equipment 91
6.2.1 Surface temperature 91
6.2.2 Arcs, sparks and high-temperature particles 92
6.2.3 Position of equipment embodying heat sources 92
6.2.4 Flammable liquids 92
6.2.5 Construction of enclosures 93
6.2.6 Live conductors 93
6.3 Precautions where particular risks of danger of fire exist 95
6.3.1 General 95
6.3.2 Conditions for evacuation in an emergency 95
6.3.3 Locations with risks of fire due to the nature of processed or
stored materials 97
6.3.4 Combustible constructional materials 98
6.3.5 Fire-propagating structures 99
6.3.6 Selection and erection of installations in locations of national,
commercial, industrial or public significance 99
6.4 Burns 100
7 Protection against overcurrent, undervoltage and overvoltage 101
7.1 General 101
7.2 Nature of protective devices 102
7.3 Protection against overload 104
7.3.1 General 104
7.3.2 Protection against overload: motors 107
7.3.3 Ring final circuits 110
7.4 Protection against fault current 110
7.5 Determination of prospective fault current 112
7.5.1 General 112
7.5.2 Calculation of inductive reactance 115
7.5.3 Evaluation of k for different temperatures 116
7.5.4 Calculation of impedance of steel enclosures 118
7.5.5 Resistance and inductive reactance values 118
7.5.6 Temperature adjustments to resistance values 119
7.5.7 Line-to-neutral short-circuits 120
7.5.8 Line-to-line short-circuits 121
7.5.9 Three-phase short-circuit 122
7.5.10 Line-to-earth faults 123
7.5.11 Fault current at the origin of an installation 125
7.6 Characteristics of protective devices 128
7.7 Overcurrent protection of conductors in parallel 131
7.8 Coordination of overload and fault current protection 134
7.9 Protection according to the nature of circuits and distribution systems 135
7.10 Protection against undervoltage 136
7.11 Protection against overvoltage 137
7.11.1 General 137