Description
Book SynopsisA practical and highly popular guide for electrical contractors of small installations, now fully revised in accordance with the latest wiring regulations The book is a clearly written practical guide on how to design and complete a range of electrical installation projects in a competitive manner, while ensuring full compliance with the new Wiring Regulations (updated late 2008). The updated regulations introduced changes in terminology, such as basic' and fault protection', and also changed the regulation numbers. This new edition reflects these changes. It discusses new sections covering domestic, commercial, industrial and agricultural projects, including material on marinas, caravan sites, and small scale floodlighting. This book provides guidance on certification and test methods, with full attention given to electrical safety requirements. Other brand new sections cover protective measures, additional protection by means of RCDs, the new cable guidelines for thin wal
Table of Contents
About the Authors xvii
Preface to the Fourth Edition xix
Acknowledgements xxv
1 Introduction 1
1.1 Layout of chapters 1
1.2 Wiring regulations 2
1.3 Terminology 2
1.4 Competence and responsibility 3
1.5 Procedures 3
1.6 Inspection and test 4
1.7 Completion 5
1.8 Working methods and materials 5
1.9 Operatives 5
1.10 Materials 5
1.11 Amendments to BS 7671: 2008 6
1.12 Voltages 6
1.13 Voltage drop 6
2 Three Bedroom House 8
2.1 The bare minimum 9
2.2 Standards 9
2.3 Building regulations 11
2.4 Load assessment 11
2.5 A typical domestic supply 12
2.6 Project specification 12
2.7 Wiring systems and cable sizes 12
2.8 Lighting 12
2.9 13 A socket-outlets 13
2.10 Cable sizes 15
2.11 Circuit protection 15
2.12 Additional protection for socket-outlets 15
2.13 Arrangement of circuits 16
2.14 Arrangement of consumer unit 16
2.15 Main switch 17
2.16 Earthing and bonding 17
2.17 Gas services bonding and external meters 18
2.18 Supplementary bonding 19
3 A Block of Retirement Flatlets 21
3.1 Two schemes 21
3.2 Early considerations 21
3.3 Other interested parties 22
3.4 Building details 22
3.5 Part 1 – Flats 24
3.6 Part 2 – Landlord’s areas 29
4 Overcurrent Protection 35
4.1 Overload 35
4.2 Overload protection 36
4.3 Overload protective devices 37
4.4 Fault current 38
4.5 Fault Current Protection 39
4.6 Omission of fault current protection 39
4.7 Short-circuit rating 39
4.8 Disconnection times 41
4.9 Earth loop impedance 42
4.10 Summary of cb specification 42
4.11 Conclusion 43
5 An Architect’s Office 44
5.1 Other interested parties 44
5.2 Building structure and finishes 45
5.3 Electrical requirements 46
5.4 Skirting system 51
5.5 Underfloor system 51
5.6 Socket-outlets 51
5.7 Lighting circuits 51
5.8 Battened out ceilings 52
5.9 Extra-Low Voltage lighting (elv) 52
5.10 Group transformers 53
5.11 Individual transformers 53
5.12 Fire prevention 53
5.13 Arrangement of circuits 53
5.14 Distribution boards 54
5.15 Cable sizes 55
5.16 Switchgear 55
5.17 Print machine 57
5.18 Wall heaters in toilets 57
5.19 Storage heaters 57
5.20 Presence of 400 Volts 58
5.21 Access to switchgear 58
5.22 Earthing and bonding 58
5.23 Main earthing terminal 58
5.24 False ceiling grid 59
5.25 Computer installations 60
5.25.1 Computer supplies 60
5.26 High protective conductor currents 60
5.27 Mains filters 60
5.28 Uninterruptible Power Supplies (UPS) 61
6 A High Street Shop 62
6.1 Special considerations 62
6.2 Other interested parties 63
6.3 Building structure and finishes 63
6.4 Electrical requirements 63
6.5 Loading and diversity 63
6.6 Lighting 65
6.7 Socket-outlets 66
6.8 Other appliances 67
6.9 Phase balance 68
6.10 Wiring systems 68
6.11 Start by considering cost 69
6.12 Shop area 69
6.13 Bakery area 69
6.14 Temperature limit of 70° C 70
6.15 Temperature limit of 90° C 70
6.16 Final selection and cable sizes 70
6.17 Bakery wiring 70
6.18 Shop wiring 71
6.19 Distribution board 71
6.20 Cable sizes 72
6.21 Switchgear 73
6.22 Isolation and switching 73
6.23 Earthing and bonding 73
6.24 Main earthing terminal (MET) 73
6.25 False-ceiling grid 74
6.26 Steel tables in the bakery 74
7 Earthing and Bonding 75
7.1 Terminology 75
7.2 Definitions 76
7.3 Green-and-yellow conductors 76
7.4 Protective earthing and protective equipotential bonding 77
7.5 Protective Multiple Earthing (PME) 77
7.6 Reliability of the earth-neutral path 78
7.7 Main bonding 79
7.8 Single fault condition 81
7.9 Supplementary bonding 82
7.10 Circuit Protective Conductors (CPCs) 82
7.11 Steel conduit and trunking 83
7.12 Steel wire armoured cable 84
7.13 Comparison of thermoplastic (PVC) and thermosetting (XLPE) armoured cable 84
7.14 Continuity of cable glands 84
7.15 Equipment having high protective conductor currents 86
7.16 Protective conductor currents 86
7.17 'High integrity' earthing 87
7.18 Earth monitoring and isolated supplies 87
7.19 Socket-outlets for desktop computers 88
7.20 Connections of protective conductors 89
7.21 Residual current devices 89
8 Car Service Workshop 90
8.1 Standards and recommendations 90
8.2 An adaptable design 91
8.3 Motor vehicle repair premises 91
8.4 Other interested parties 91
8.5 Building structure and finishes 91
8.6 Construction 94
8.7 Electrical requirements 94
8.8 Health and safety executive guidance and regulations 94
8.9 Health and safety guidance note HSG 261 95
8.10 Wiring regulations 96
8.11 Load assessment and maximum demand 96
8.12 Maximum demand load and diversity 96
8.13 Lighting 97
8.14 Welder 99
8.15 Compressor 99
8.16 Gas blowers 100
8.17 Phase balance 100
8.18 Estimate of maximum demand 101
8.19 What about a distribution circuit (sub-main)? 102
8.20 Wiring systems 102
8.21 Workshop 102
8.22 Office 105
8.23 Arrangement of circuits 105
8.24 Distribution boards 105
8.25 Cable sizes 105
8.26 Isolation and switching 107
8.27 Machinery 107
8.28 Cooker 107
8.29 Gas boiler 107
8.30 110 V transformer 108
8.31 Earthing and bonding 108
8.32 Main earthing terminal 109
8.33 Protective conductors at distribution board B 109
8.34 Armoured cable glands 109
8.35 Steel conduit and trunking 110
9 Circuits 111
9.1 Terminology 111
9.2 Colours of three phases 111
9.3 Conventional circuits 112
9.4 Lighting circuits 112
9.5 Induction 113
9.6 Socket-outlet circuits 113
9.7 Changing methods 113
9.8 Ring main obsolescence 113
9.9 History of the ring final circuit 114
9.10 Times have changed 114
9.11 Alternative methods 116
9.12 Radial circuits 117
9.13 Introducing the tree 117
9.14 20 A tree 117
9.14.1 Domestic 117
9.14.2 Commercial and similar 117
9.15 32 A tree 118
9.16 Switching and control 119
9.17 Comparison of systems 120
9.18 32 A ring final circuit 120
9.19 20 A tree 121
9.20 Composite circuits 121
10 Farming and Horticulture 123
10.1 Why farms are different 124
10.2 Special earthing requirements on farms with TT systems 126
10.3 Earth electrodes 127
10.4 Alternative electrodes 127
10.5 Bonding 128
10.6 Supplementary bonding 129
10.7 Residual current devices 129
10.8 Shock protection 130
10.9 General requirements for automatic disconnection of supply (ADS) 131
10.10 Fire protection 132
10.11 Automatic life support for high density livestock rearing 132
10.12 Switchgear 133
10.13 Wiring systems 134
10.14 Overhead or underground wiring 134
10.15 Non-metallic wiring systems 135
10.16 Steel Wire Armoured (SWA) cable 136
10.17 Twin and earth cable 136
10.18 General rules regarding farm electrical installations 136
11 Isolation and Switching 138
11.1 Isolation and switching 138
11.2 Isolation 139
11.3 Mechanical maintenance 140
11.4 Emergency switching 141
11.5 Labelling and notices 143
12 A Village Sports Centre 145
12.1 Special conditions 145
12.2 Codes of practice 145
12.3 Other interested parties 146
12.4 Building details 146
12.5 Structure and finishes 147
12.6 Electricity supply and requirements 148
12.7 Off-peak tariff 148
12.8 Normal tariff 148
12.9 Load assessment and diversity 150
12.10 Off-peak heating 150
12.11 Normal tariff 150
12.12 Total estimated maximum current demand 152
12.13 Wiring systems 152
12.14 Circuitry and cable sizing 154
12.15 Cable grouping factors 155
12.16 Arrangement of circuits 156
12.17 Switchgear 157
12.18 Shock protection 157
12.19 Earthing 157
12.20 Bonding 157
12.21 An occasional problem 157
12.22 Solutions 158
12.23 Requirements for a TT installation 159
13 An Indoor Swimming Pool 160
13.1 Special conditions 160
13.2 Other interested parties 161
13.3 Building details 161
13.4 Application of zoning to this project 162
13.5 Dehumidifiers 167
13.6 Changing room/shower area 167
13.7 Loading and diversity for the swimming pool project 168
13.8 Wiring systems 169
13.9 Cable sizes 170
13.10 Distribution board 170
13.11 Isolation 171
13.12 110 V system 171
13.13 Earthing 172
13.14 Local supplementary bonding 172
13.15 Floor grid 172
14 Cables and Wiring Systems 174
14.1 External influences 174
14.2 Cost considerations 175
14.3 Choosing suitable cable routes 175
14.4 Is armouring always necessary? 175
14.5 Fire barriers 175
14.6 Holes through fire barriers 176
14.7 Sealing the wiring system 176
14.8 Work in progress 176
14.9 Records 177
14.10 Hidden cables 177
14.11 Cables within a floor 177
14.12 Cables above false ceilings 178
14.13 Cables in walls 178
14.14 Mechanically protected cables 179
14.15 Fire and smoke 179
14.16 Thermoplastic (PVC) insulation 180
14.17 Thermosetting (XLPE) 181
14.18 Silicone rubber 181
14.19 Low smoke zero halogen (LS0H) 181
14.20 Mineral insulated copper sheathed (MICS) cables 182
14.21 Heat transference from cables 182
14.22 Wiring systems and cable management 182
14.23 Emergency systems 182
14.24 Care with wiring systems 183
14.25 Thermoplastic (PVC) insulated and sheathed cables 183
14.26 Thermosetting (PVC) insulated conduit cables 183
14.27 Steel conduit systems and trunking 184
14.28 Plastic conduit systems and trunking 184
14.29 MICS cables 184
14.30 Steel wire armoured cables 185
14.31 Silicone insulated PVC sheathed cables 185
15 Inspection, Testing and Certification 186
15.1 Labelling and documentation 187
15.2 Specification and manual 187
15.3 Regulations 187
15.4 Electrical installation certificate (EIC) 187
15.5 Signatories 190
15.6 Alterations and additions 192
15.7 Limits of responsibility 192
15.8 Deviations and departures 193
15.9 New materials and inventions 193
15.10 Particulars of the installation 194
15.11 Inspections and test schedules 194
15.12 Inspection procedures 194
15.13 Testing 197
15.14 Continuity testing 198
15.15 Polarity 198
15.16 Continuity of protective conductors 198
15.17 Continuity of ring circuit conductors 198
15.18 Insulation resistance 200
15.19 Earth fault loop impedance 202
15.20 Supply impedance Ze 204
15.21 Earth loop impedance of circuits Zs 205
15.22 Prospective fault current 206
15.23 Operation of residual current devices 206
16 A Caravan Park 208
16.1 Measures for protection against electric shock 208
16.2 Earthing arrangements 209
16.3 PME must not be used for caravans 209
16.4 Electrical equipment (external influences) 210
16.5 Wiring systems 210
16.6 Cables buried in the ground 210
16.7 Overhead cables 210
16.8 Caravan pitch electrical supply equipment 211
16.9 Plugs and socket-outlets 211
17 Residual Current Devices 213
17.1 How does an RCD work? 214
17.2 Fault protection 214
17.3 Additional protection 217
17.4 Requirements to provide additional protection by RCDs 217
17.5 RCDs incorporated into a consumer unit, to meet the requirements for additional protection 218
17.6 Protection against fire 220
17.7 Avoiding a hazard and/or minimising an inconvenience due to the tripping of an RCD 221
17.8 Reducing the possibility of unwanted tripping of RCDs 221
17.9 Use of a ‘front-end’ 30 mA RCD is generally considered unacceptable practice 222
17.10 Installations forming part of a T T system 222
17.11 RCDs connected in series 223
17.12 Labelling 223
18 Flood Lighting (Outdoor Lighting) Project 224
18.1 Lighting arrangement 224
18.2 General requirements 224
18.3 Wiring system 225
18.4 Protective measures 226
18.5 Load assessment 226
18.6 Rating of the overcurrent protective device 227
18.7 Circuit design 227
18.8 Voltage drop consideration 228
18.9 Switchgear 230
19 Circuit Design Calculations 231
19.1 Design process 231
19.2 Protective conductors 235
19.3 Worked example 235
19.4 Solution 236
Index 239
