Guide to the IET Wiring Regulations

Electrical Contractors' Association (ECA), ESCA House, London, UKThe Electrical Contractors' Association (ECA) is the UK's leading trade association for contractors who design, install, inspect, test and maintain electrical and electronic equipment and services. In its capacity to work with regulatory bodies and government to lead on issues including safety, training, qualification and technological development, ECA is represented on the committees which regularly reviews and updates British Standards on electrical wiring regulations, used in the UK and many commonwealth countries. The ECA has partnered with Wiley on a number of successful books on key topics of interest to its membership.

• Foreword by Giuliano Digilio xiPreface xiiiAcknowledgements xvChapter A – BS 7671:2008 Amd No. 1:2011 Requirements for Electrical Installations – Introduction and Overview 1A 1 Introduction to BS 7671:2008 1A 2 Plan and layout of BS 7671:2008 2A 3 Overview of major changes 5A 4 Amendment No. 1:2011 9Chapter B – Legal Relationship and General Requirements of BS 7671:2008 Amd No. 1:2011 11B 1 Legal requirements and relationship 11B 1.1 Key legal UK legislation 11B 1.2 The Electricity at Work Regulations 1989 (EWR 1989) 12B 1.3 The Electricity Safety, Quality and Continuity Regulations 2002(as amended) 13B 1.4 The Electricity Act 1984 (as amended) 14B 1.5 The Building Act 1984, The Building Regulations and Part P 14B 1.6 The Electromagnetic Compatibility Regulations 2006 15B 1.7 Tort and negligence 15B 2 The role of Standards 17B 3 Part 3 of BS 7671:2008 – assessment of general characteristics 18Chapter C – Circuitry and Related Parts of BS 7671:2008 Amd No. 1:2011 21C 1 Introduction 21C 2 Design procedure overview 21C 3 Load assessment 23C 3.1 Principles and definitions 23C 3.2 Maximum demand assessment 24C 3.3 Diversity 25C 4 Circuitry design 26C 4.1 Introduction 26C 4.2 Protection against overcurrent in general 28C 4.3 Overload protection 28C 4.4 Fault protection 40C 4.5 Voltage drop 44C 4.6 Disconnection and electric shock protection 49C 5 Sub-mains 56C 5.1 Diversity 56C 5.2 Distribution circuit (sub-main) selection 57C 5.3 Armouring as a CPC 57C 5.4 Automatic disconnection for sub-mains 58C 6 Discrimination co-ordination 58C 6.1 Principles and system co-ordination 58C 6.2 Fuse-to-fuse discrimination 59C 6.3 Circuit breaker to circuit breaker discrimination 60C 6.4 Circuit breaker to fuse discrimination 62C 7 Parallel cables 62C 7.1 General and BS 7671 requirements 62C 7.2 Unequal current sharing 63C 8 Harmonics 63C 8.1 Requirements 63C 8.2 Harmonic assessment 63C 9 Standard final circuit designs 64C 9.1 Introduction and scope 64C 9.2 Standard domestic circuits 72C 9.3 All purpose standard final circuits 73C 10 RcDs and circuitry 73C 10.1 Introduction – increased use of RcDs 73C 10.2 consumer unit arrangements for RcDs 74C 11 Ring and radial final circuits 75C 11.1 Introduction 75C 11.2 Ring final circuits 75C 11.3 Radial final circuits 77Chapter D – Selection and Erection – Equipment 79D 1 Introduction and fundamentals 79D 2 Compliance with Standards 80D 3 Identification of conductors – introduction 81D 3.1 Principle of required identification (Regulation 514.3.1) 81D 3.2 Identification by colour 83D 3.3 Identification by marking 85D 3.4 Alterations and additions – identification 85D 3.5 Interface marking 85D 3.6 DC identification 86D 4 Protection against voltage and electromagnetic disturbance 86D 4.1 General 86D 4.2 Electromagnetic compatibility and prevention of mutual detrimental influences 88D 5 Wiring systems 95D 5.1 The choice of wiring systems 95D 5.2 Circulating currents and eddy currents in single-core installations 98D 5.3 Electrical connections and joints 100D 5.4 Wiring systems – minimizing spread of fire 104D 5.5 Proximity to other services 106D 6 Circuit breakers 106D 6.1 General 106D 6.2 Operation and characteristics 107D 6.3 Ambient temperature de-rating 110D 7 Residual current devices 111D 7.1 BS 7671 applications 111D 7.2 Operation and BS 7671 requirements 112D 7.3 Unwanted RCD tripping and discrimination 113D 7.4 d.c. issues for RCDs 115D 7.5 TT installations and RCDs 115D 8 Other equipment 116D 8.1 Isolation and switching 116D 8.2 Consumer units for domestic installations 116D 8.3 Overvoltage, undervoltage and electromagnetic disturbances 116D 8.4 Surge protective devices 118D 8.5 Insulation monitoring devices (IMDs) 118D 8.6 Residual current monitors (RCMs) 119D 9 Generating sets 121D 10 Rotating machines 121D 11 Plugs and socket-outlets 122D 12 Electrode water heaters and electrode boilers 123D 13 Heating conductors 124D 14 Lighting and luminaires 124D 15 Safety services 127D 15.1 Introduction 127D 15.2 Classification of break times 127D 15.3 Safety sources 127D 15.4 Circuits for safety services 127D 16 Ingress protection (IP), external influences 129D 16.1 General 129D 16.2 Equipment applications and examples 131ftoc.indd 7 11/15/2021 21:34:01Chapter E – Earthing and Bonding 133E 1 Introduction 133E 2 Earthing arrangements 133E 3 General requirements of earthing and bonding 138E 4 Protective conductors 139E 4.1 General 139E 4.2 Physical types of protective conductor 140E 4.3 Sizing protective conductors 141E 4.4 Protective conductors up to 16 mm 2 142E 4.5 The earthing conductor 146E 5 Armoured cables as protective conductors 147E 5.1 General 147E 5.2 ERA Report on current sharing between armouring and CPC 148E 5.3 ECA advice and recommendations 148E 6 Protective bonding 149E 6.1 Purpose of protective equipotential bonding 149E 6.2 BS 7671 requirements 149E 6.3 Bonding solutions for the modern installation 149E 6.4 Sizing main bonding conductors 154E 6.5 Domestic protective bonding layouts 155E 6.6 Supplementary equipotential bonding 157E 7 High earth leakage installations 158Chapter F – Inspection Testing and Certification (Part 6) 161F 1 Introduction 161F 1.1 Inspection and testing – an integrated procedure 161F 2 Visual inspection 162F 3 Testing 164F 3.1 Introduction – pass and fail nature 164F 3.2 Required tests 164F 3.3 Continuity testing 165F 3.4 Ring continuity 168F 3.5 Insulation resistance testing 171F 3.6 Polarity testing 174F 3.7 Earth fault loop impedance (ELI) testing 175F 3.8 Prospective fault current testing 179F 3.9 Testing RCDs and other functional tests 181F 3.10 Verification of voltage drop 182F 4 Certification paperwork 183F 4.1 Introduction, various certificates and schedules 183F 4.2 Overview of certificates and schedules 184F 4.3 Completing the paperwork 184Chapter G – Special Locations 201G 1 Introduction purpose and principles 201G 1.1 Introduction 201G 1.2 Purpose and principles 201G 1.3 Particular requirements and numbering 202G 2 Locations containing a bath or shower (701) 203G 2.1 Introduction and risks 203G 2.2 Zone concept 203G 2.3 Electric shock requirements 204G 2.4 Equipment selection and erection 207G 3 Swimming pools and other basins (702) 208G 3.1 Introduction and risks 208G 3.2 Zone concept 209G 3.3 Requirements and guidance 211G 4 Agricultural and horticultural premises (705) 214G 4.1 Introduction, purpose and principles 214G 4.2 Requirements and guidance 214G 5 Caravan parks and camping parks (708) 218G 5.1 Introduction purpose and principles 218G 5.2 Requirements and guidance 218G 6 Medical locations (710) 222G 6.1 Introduction and risks 222G 6.2 Medical groups and class of safety service supply 222G 6.3 Requirements 223G 7 Exhibitions, shows and stands (711) 227G 7.1 Introduction and risks 227G 7.2 Requirements and guidance 228G 8 Solar photovoltaic (PV) power supply systems (712) 229G 8.1 Introduction principles and terminology 229G 8.2 Requirements 231G 8.3 Notes and guidance 232G 9 Mobile or transportable units (717) 235G 9.1 Scope and application 235G 9.2 Requirements 235G 9.3 Notes and guidance 236G 10 Floor and ceiling heating systems (753) 237G 10.1 Introduction 237G 10.2 Requirements 238G 10.3 Notes and guidance 238References 240Appendices 243Appendix 1 – Standards and bibliography 244Appendix 2 – Popular cables: current rating tables from BS 7671:2008 Appendix 4 249Appendix 3 – Limiting earth fault loop impedance tables from BS 7671:2008 252Appendix 4 – Cable data resistance, impedance and ‘R1 + R2’ values 254Appendix 5 – Fuse I2t characteristics 258Index 259