IET Guidance Note 8 Earthing & Bonding BS7671:2018+A2:2022 5th Edition 2022 (PDF)

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About the book:

Publisher: IET
Place of Publication: United Kingdom
Pages: 209
Edition: 2022
Language: English
Size: 94 Mb

Complies with BS7671:201 8+A2:2022.

Content:

Cooperating organizations
Acknowledgements 8
Preface 9
Introduction 11
Chapter 1 Protective earthing 13
1.1 Protective earthing 13
1.2 Source earthing 13
1.3 The purpose of source earthing 14
1.4 The purpose of electrical equipment earthing 14
Chapter 2 The means of earthing 17
2.1 The means of earthing 17
2.2 Distribution network operators’ facilities 18
2.3 Earth electrodes 18
2.4 Rod electrodes 19
2.5 Tape and wire electrodes 21
2.6 Plate electrodes 2 2
2.7 Structural metalwork electrodes 23
2.8 Lead sheaths and other metal coverings of cables for electrodes 24
2.9 Location of the installation earth electrode 24
2.10 Resistance of the earth electrode 25
2.10.1 Calculating the resistance of a rod electrode 27
2.10.2 Calculating the resistance of a plate electrode 28
2.10.3 Calculating the resistance of a tape electrode 28
2.10.4 Limiting values of the electrode resistance for TT systems 29
2.11 Electrode installation 29
2.12 Electrode loading capacity 31
2.13 Earth electrode resistance testing 31
2.14 Determination of the external earth fault loop impedance, Ze 36
2.15 Responsibility for providing a means of earthing 38
Chapter 3 The earthing conductor 39
3.1 The earthing conductor 39
3.2 The cross-sectional area of an earthing conductor 40
3.3 The csa of a buried earthing conductor 42
3.4 Minimum csa of an earthing conductor 42
3.5 Impedance contribution of an earthing conductor 43
3.6 Colour identification of an earthing conductor 43
3.7 Protection of an earthing conductor against external influences 43
3.8 Disconnection of the earthing conductor 44
3.9 Connection of the earthing conductor to the means of earthing 44
Chapter 4 System types and earthing arrangements 45
4.1 A system 45
4.2 TN-C system 46
4.3 TN-S system 48
4.4 TN-C-S system 5 0
4.5 TT system 52
4.6 IT system 5 4
Chapter 5 Protective equipotential bonding 57
5.1 The purpose of protective equipotential bonding 5 7
5.2 Main protective bonding conductors 61
5.2.1 Cross-sectional area (csa) 63
5.2.2 Identification 65
5.2.3 Supports 6 6
5.2.4 Additions and alterations 67
5.3 Earth-free local equipotential bonding 68
5.4 Bonding of lightning protection systems 70
5.5 Extraneous-conductive-parts common to a number of buildings 71
5.6 Installations serving more than one building 73
5.7 Multi-occupancy premises 7 7
Chapter 6 Extraneous-conductive-parts and their connections
6.1 Definition of an extraneous-conductive-part 79
6.2 Some examples of extraneous-conductive-parts 81
6.3 An example of a conductive part which is not an extraneous-conductive-part 82
6.4 Connection to pipework 82
6.5 Connections to structural steelwork and buried steel grids 8 6
Chapter 7 Automatic disconnection 87
7.1 Automatic disconnection of supply (ADS) 87
7.2 TN systems 87
7.2.1 Earth fault loop impedance 88
7.2.2 Automatic disconnection using a residual current device (RCD) in TN systems 93
7.3 TT systems 94
7.4 IT systems 95
7.5 Additional protection 97
7.6 Residual current devices (RCDs) in series 97
7.6.1 Selecting appropriate RCDs 99
7.7 Automatic disconnection for reduced low voltage systems 99
7.8 Automatic disconnection and alternative supplies 103
7.9 Separated extra-low voltage systems (SELV) 103
7.10 Protective extra-low voltage systems (PELV) 104
7.11 Functional extra-low voltage systems (FELV) 105
7.12 Overvoltages imposed on the low voltage system due to high voltage system earth faults 106
Chapters Supplementary protective equipotential bonding
8.1 The purpose of supplementary protective equipotential bonding 107
8.2 Supplementary bonding conductor types 109
8.3 Cross-sectional area (csa) of supplementary bonding conductors 110
8.4 Limitations on resistance of supplementary bonding conductors 111
8.5 Supports for supplementary bonding conductors 111
8.6 Locations containing a bath or shower 112
8.7 Shower cabinet located in a bedroom 116
8.8 Swimming pools and other basins 116
8.9 Agricultural and horticultural premises 120
8.10 Conducting locations with restricted movement 124
8.10.1 Medical locations 126
8.11 Temporary electrical installations for structures, amusement devices and booths at fairgrounds, amusement parks and circuses 126
8.12 Static convertors 126
8.13 Other locations of increased risk 127
8.14 Where automatic disconnection is not feasible 127
Chapter 9 Circuit protective conductors 129
9.1 Circuit protective conductors 129
9.2 Cross-sectional area 130
9.2.1 Calculation of csa - general case 130
9.2.2 Selection of csa - general case 132
9.2.3 Non-copper cpcs 133
9.2.4 Evaluation of k 133
9.3 Armouring 134
9.3.1 Calculation of csa - armoured cable 135
9.3.2 Selection of csa - armoured cable 135
9.3.3 Contribution to earth fault loop impedance 135
9.3.4 Armouring inadequate for a cpc 135
9.3.5 Termination of armoured cables 136
9.4 Steel conduit 138
9.4.1 Calculation of csa - steel conduit 138
9.4.2 Selection of csa - steel conduit 139
9.4.3 Maintaining protective conductor continuity 140
9.5 Steel trunking and ducting 140
9.5.1 Maintaining protective conductor continuity 141
9.6 Other metal enclosures 141
9.7 Terminations in accessories 141
9.8 Circuit protective conductor for protective and functional purposes 144
9.9 Significant protective conductor currents 145
9.9.1 Equipment 148
9.9.2 Labelling at distribution boards 149
9.9.3 Ring final circuits 149
9.9.4 Radial final circuits 149
9.9.5 Busbar systems 150
9.9.6 Connection of an item of equipment (protective conductor current exceeding 10 mA) 151
9.9.7 TT systems 152
9.9.8 Residual current devices 153
9.10 Earth monitoring 153
9.11 Proving continuity 1 54
Chapter 10 Particular issues of earthing and bonding 155
10.1 Clean earths 155
10.2 Protective multiple earthing for caravan parks 156
10.3 Exterior semi-concealed gas meters 158
10.4 Small-scale embedded generators 158
10.4.1 Statutory regulations 158
10.4.2 Engineering Recommendation G98 159
10.4.3 Means of isolation 160
10.4.4 Warning notices 161
10.4.5 Up-to-date information 161
10.4.6 Solar photovoltaic (PV) power supply systems 162
10.5 Mobile and transportable units 162
10.5.1 The term 'mobile or transportable unit' 162
10.5.2 Examples of mobile or transportable units 163
10.5.3 The risks 163
10.5.4 Reduction of risks 163
10.5.5 Supplies 164
10.5.6 TN-C-S with PME 164
10.5.7 Protective measures 165
10.5.8 Additional protection 165
10.6 Highway power supplies and street furniture 166
10.6.1 Street furniture 166
10.6.2 Street furniture access doors 166
10.6.3 Earthing of Class I equipment within street furniture 167
10.6.4 Distribution circuits 167
10.7 Suspended ceilings and raised access floor systems 167
10.7.1 Suspended ceilings 167
10.7.2 Raised access floor systems 168
10.8 Exhibitions, shows and stands 169
10.8.1 Protection by automatic disconnection of supply 169
10.8.2 Distribution circuits 169
10.8.3 Installations incorporating a generator 169
10.8.4 Socket-outlets 170
10.9 MedicalI locations 170
10.9.1 Type of system earthing 170
10.9.2 SELV and PELV 170
10.9.3 Fault protection 171
10.9.4 TT systems 171
10.9.5 Medical IT systems 171
10.9.6 Transformers for a medical IT system 172
10.9.7 Supplementary protective equipotential bonding 173
10.10 Marinas and similar locations 174
10.10.1 The risks 174
10.10.2 Minimizing the risks 175
10.10.3 Protection against electric shock 175
10.10.4 TN system 175
10.11 Cable tray and cable basket, and other metallic containment systems 177
10.12 Electromagnetic compatibility earthing and bonding 178
10.13 Electric vehicle charging installations 178
Appendix A Values of k for various forms of protective conductor 179
Appendix B Data for armoured cables 181
Index 185

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