Electrical Installation Designs 4e

Mr. Bill Atkinson (deceased) Bill Atkinson was the writer's pseudonym used by Alan Smith, the original author of the book. He worked in the electrical installation industry and at the NICEIC. Mr. Roger Lovegrove, Consultant, Surrey, UK Roger Lovegrove is an electrical consultant. He is a member of the Electrical Contractors' Association techinical committees and of the joint IEE/BSI Wiring Regulations committee. With his vast knowledge in this area of electrical engineering, he has updated Bill Atkinson s original text for this fourth edtition. Mr. Gary Gundry, Senior Engineer, Electrical Safety Council, UK Mr Gundry worked for Seeboard and Eastern Electricity, before becoming a lecturer at Lowestoft College, teaching electrical contracting and electrical engineering up to HNC level. He joined NICEIC in 1999 after spending three years as a Director and Qualified Supervisor of a business enrolled as an Approved Contractor, where he worked in the Standards division on the NICEIC Technical Manual. He is now Senior Engineer at Electrical Safety Council. Mr. Martyn Allen, Senior Engineer, Electrical Safety Council Martyn Allen's experience in the electrical installation industry spans 30 years. He served an apprenticeship and worked as an electrician with British Coal, spent 16 years in engineering insurance risk management and then joined the Electrical Safety Council. He is a Chartered Electrical Engineer and Corporate Member of the IET. He is a member of the Joint Technical Committee JPEL/64 Panel C Shock Protection and Isolation and Switching.

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 70degree C 70 6.15 Temperature limit of 90degree 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