Table of Contents
Table of Contents
This edition first published 2012
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Library of Congress Cataloging-in-Publication Data
Guide to the IET wiring regulations : 17th edition IET wiring regulations (BS 7671:2008 incorporating Amendment no. 1:2011) / Electrical Contractors’ Association.
p. cm.
Includes bibliographical references and index.
ISBN 978-1-119-96514-5 (pbk.)
ISBN 978-1-119-94075-3 (epdf)
ISBN 978-1-119-94169-9 (epub)
ISBN 978-1-119-94170-5 (mobi)
1. Electric wiring–Insurance requirements–Handbooks, manuals, etc. 2. Electric wiring, Interior–Handbooks, manuals, etc. I. Electrical Contractors’ Association (Great Britain)
TK3275.G85 2012
621.319'24–dc23
2011047222
A catalogue record for this book is available from the British Library.
Paper ISBN: 9781119965145
Foreword by Giuliano Digilio
Head of Technical Services, Electrical Contractors’ Association (ECA)
Amendment No. 1:2011 of the IEE Wiring Regulations BS 7671:2008 includes a name change; they are now known as the IET Wiring Regulations BS 7671:2008 Amd No. 1:2011.
The IEE Wiring Regulations, and more lately BS 7671, have always been important for electrical contractors and for installation designers, and they are a key factor in the implementation of electrical safety within the UK and indeed overseas. The IEE Wiring Regulations go back to the end of the 19th century, almost to the time of the very first electrical installation within the UK.
The ECA is fully committed to the development of standards for the national BS 7671 committee as well as corresponding work in both the European Committee for Electrotechnical Standardisation (CENELEC) and the International Electrotechnical Commission (IEC). This includes a considerable amount of work in the preparation for BS 7671:2008 Amd No. 1:2011.
I am pleased that you have purchased the ECA’s Guide to the IET Wiring Regulations and I trust that this quality publication will aid to enhance the understanding and knowledge within the electrical industry for both electrical contractors and electrical designers.
Preface
This guide discusses the requirements of BS 7671:2008 including Amendment No. 1:2011, also known as the IET Wiring Regulations 17th Edition.
It has been published by the Electrical Contractors’ Association to help their members and the contracting industry at large to understand and apply the IET Wiring Regulations.
This guide is a valuable resource for all users of BS 7671 including apprentices and electricians who perhaps want to ‘dig a bit deeper’ into the background of the Regulations, together with electrical technicians, installation engineers and design engineers. Most individuals who have any involvement with BS 7671 will find the book of considerable help and benefit in their everyday work.
Steve Mitchell
Divisional Director
Electrical Contractors’ Association
Acknowledgements
The ECA are very pleased to acknowledge the contribution made to this revision of the guide by Giuliano Digilio, Head of Technical Services and Graeme Wool, Principal Engineer.
Paul Cook, former staff member of the IET, is thanked for his assistance with the reviewing and updating work on this publication in line with Amendment No. 1 of BS 7671:2008 ‘Requirements for Electrical Installations’.
Steve Mitchell
Divisional Director
Electrical Contractors’ Association
A
BS 7671:2008 Amd No. 1:2011 Requirements for Electrical Installations – Introduction and Overview
A 1 Introduction to BS 7671:2008
BS 7671:2008 Requirements for Electrical Installations was published in January 2008, and amendments were incorporated in 2011.
Although the document is a British Standard, it is also known (and jointly labelled as) as the ‘IET Wiring Regulations Seventeenth Edition’.
Throughout this book, BS 7671:2008 incorporating Amendment No. 1:2011 is referred to as BS 7671:2008, BS 7671, the Wiring Regulations, the Regulations, the 17th edition or the Standard, depending upon the particular context.
The British National Committee is obliged to publish the technical intent of the CENELEC harmonization documents (HDs). However the committee have gone further and published the HDs verbatim, except where there is a more up to date International Electrotechnical Commission (IEC) standard and, in a few instances, where national circumstances warrant changes.
The general structure of IEC, CENELEC and BS 7671 is illustrated in Figure .
Most of the document originates from CENELEC in ‘harmonized documents’ (HDs). The parent document is known as the HD 60384 series and includes virtually all parts of the installation standard.
Within BS 7671:2008 there are now only a few regulations that are truly ‘UK only’, although some of the CENELEC parts of HD 60384 have been modified, cut, or expanded upon for BS 7671. Some of the appendices of BS 7671 are home grown.
The Wiring Regulations Committee has also used certain parts of the corresponding IEC document IEC 60364, either modified or virtually unmodified.
A list of the parts of the HD 60384 series used in BS 7671:2008 is shown in Table .
A 2 Plan and Layout of BS 7671:2008
Most users will not need to concern themselves with the correct terminology for groups of regulations and chapters etc, but an explanation of this has been added for completeness.
Let’s look at a single regulation such as 411.3.2.1 and provide a diagram of the structure.
Taking the first three digits, they relate as follows:
The remaining numbers make up the group, sub-set and regulation, but really only the group is of any significance:
There are seven parts to BS 7671:2008, they are as follows:
Part | Contents |
1 | Scope, Object and Fundamental Principles |
2 | Definitions |
3 | Assessment of General Characteristics |
4 | Protection For Safety |
5 | Selection and Erection of Equipment |
6 | Inspection and Testing |
7 | Special Installation or Locations |
A 3 Overview of Major Changes
Most of the document has remained unchanged compared to the 16th Edition; many changes were due to formal incorporations of CENELEC drafts required for harmonization.
This section gives an overview of technical changes that will lead to a change in practice, or something that you should be aware of. As stated in the preface, the subject of BS 7671 can be very dry and this part of the book has been kept as short as possible. Readers may wish to skip this part of the book and start with the two key Chapters; these being Chapters C and D.
The following overview notes have been included in order of significance.
Chapter 41 – protection Against Electric Shock
Revision to Chapter 41 is probably the most significant made for the 17th Edition.
The whole structure of the chapter has been modified. The familiar terms used in the 16th Edition of ‘direct contact’ and ‘indirect contact’ have been replaced with ‘basic protection’ and ‘fault protection’ respectfully (see Figure ). This terminology change by itself had ramifications on many other parts of the Regulations and these brought about logistical modifications. The various measurers are termed ‘protective measurers’.
The structure of Chapter 41 was modified accordingly. Basic protection (insulation and enclosures) was considered something that designers and installers did not actually ‘consider’ and was shunted towards the rear of the chapter. The extremely rare measurers of ‘placing out of reach’, ‘obstacles’, ‘non-conducting locations’, ‘earth free local equipotential bonding’ and electrical separation were shunted further to the rear of the chapter. Thus the main reading in the front end of Chapter 41 is about automatic disconnection.
There have also been changes to protective device disconnection times. There are not any ‘mixed’ disconnection times and disconnection times for TT earthing systems have been reduced. As protection in TT installations will virtually always require a RCD, the reduced disconnection times in the 17th Edition are easily achieved (0.2 seconds on final circuits).
A very significant new regulation (411.3.3) requires a 30mA RCD additional protection for socket-outlet circuits that are intended for use by ordinary persons. With a few exceptions, this means all domestic installations. Commercial installations will generally remain exempt, as in most situations individuals will have received instruction.
Guidance on the structure, disconnection times and the use of RCDs is given in Chapter C of this book.
Bathrooms 701
The 17th Edition goes a bit further on harmonization with CENELEC for bathroom installations.
The 16th Edition introduced the concept of zones to the regulations for bathrooms but fell short of harmonization with Europe in one key area: socket-outlets in bathrooms.
Section 701 now aligns with the European ethos, there is not any Zone 3. Thus outside of Zone 2, which is 600 mm from the bath or shower outer edge, only the ‘general rules’ of the regulations apply and any equipment is allowed. However, socket-outlets have a special distance specified, which is at least 3m from the boundary of Zone 1.
All bathroom circuits now require 30mA RCD additional protection and a UK modification allows supplementary equipotential bonding to be omitted, under certain conditions.
Tables and Methods of Cable Current-Carrying Capacity (Appendix 4 of BS 7671)
The whole of the first part of this appendix was modified for the 17th Edition and has been further modified by Amendment No. 1 with respect to calculating the current rating of cables laid in the ground.
Swimming Pools and Other Basins (702)
For the 17th Edition, the scope of this section now includes the basins of fountains and areas of natural water including the sea and lakes, where they are specifically designated as swimming areas.
Lighting and Luminaires
A completely new section for the 17th Edition is Section 559 ‘Luminaires and Lighting Installations’; which contains six pages of text and some 36 new regulations.
The new section deals with interior and exterior lighting installations and also applies to highway power supplies and street furniture.
The section specifies regulations for luminaire through-wiring and heat specification of terminal wiring and similar items. Through-wiring is only permitted where the luminaire is specifically designed for it.
Inspecting and Testing
There is a new requirement that insulation resistance is measured between live conductors and the cpc, with the cpc connected to the earthing arrangement.
Periodic Inspection
Whilst the text of Chapter 62 Periodic Inspection and Testing is unchanged, the forms in Appendix 6 have been substantially changed. They now detail extensive inspection requirements.
New Appendix with Current-Carrying Capacity of Busbars
A new appendix has been added giving information on current-carrying capacity and voltage drop limitations for busbars and powertrack.
Chapter 56 – Safety Services
This chapter has been modified and specifies ‘break times’ for standby systems. It sets regulations for subjects like circuitry under fault conditions, parallel operation and specifies the life of certain critical back up batteries.
High Earth Leakage Currents
Correctly termed ‘high protective conductor currents’, the former Section 607 has been incorporated into Chapter 54, with some limited removal of ambiguous regulations.
High Voltage to Low Voltage Faults
This is a new section for the 17th Edition, but this is not particularly significant for installers or designers; the section is only relevant for ‘private’ HV-LV sub-stations and even then the corresponding HV standards will need to be followed. Read Chapter D for a fuller explanation.
Voltage Drop
Whilst in essence the basic requirements of the regulations on voltage drop have not fundamentally changed, a new appendix suggests maximum voltage drops for both utility and private supplies. These voltage drops are separated into suggested limits for lighting and other circuits.
Atmospheric and Switching Overvoltages
There are a few pages of regulations on this subject but they are not of much significance, unless you have overhead distribution cables within your installation.
Surge Protective Devices
Although these are not generally required, there are regulations for installing surge protective devices.
Insulation Monitoring Devices (IMDs) and Residual Current Monitors (RCMs)
Similarly, although not specified, there are regulations for installing these devices. RCMs in particular are becoming more widely specified and there is guidance on this subject provided in Chapter D of this book.
Caravan and Camping Parks (708)
The main modification for the 17th Edition is that pitch socket-outlets are to be individually protected by a 30mA RCD.
New Special Installations or Locations
The following Special Installations sections are new to the 17th Edition:
709 Marinas
711 Exhibitions shows and stands
712 Solar photovoltaic (PV) power supply systems
717 Mobile or transportable units
721 Electrical installations in caravans and motor caravans
740 Temporary electrical installations for structures, amusements and booths at fairgrounds
753 Floor and ceiling heating systems
A 4 Amendment No. 1:2011
The first amendment to BS 7671:2008 was issued on 1 July 2011 and is intended to come into effect on 1 January 2012. Installations designed (but not installed) after 31 December 2011 are to comply with BS 7671:2008 Amd No. 1.
The major changes are as follows:
Section 444 Measures Against Electromagnetic Disturbances
The new section includes mainly advice that consideration should be given to aspects of the installation relating to electromagnetic interference. However, there are also some specific requirements; e.g.
444.5.1.1 all protective and functional earthing conductors of an installation within a building shall be connected to the main earthing terminal
444.4.3.3 where a complete low voltage installation including the transformer is operated only by the user, an installation forming part of a TN-S system shall be installed
444.4.6 for TN or TT multiple-source power supplies to an installation, the system shall be earthed at one point only.
Section 534 Devices for Protection Against Overvoltage
Where Section 443 requires protection against overvoltage, surge protective devices must be selected in accordance with the new Section 534.2. In the UK (see regulation 443.2.2) it is likely that protection against overvoltage will not be required.
Part 6 Inspection and Testing
New detailed periodic inspection report forms are introduced in Appendix 6.
Part 7 New Specialist Installation Section
Section 710 – medical locations
Section 729 – operating and maintenance gangways
Appendices
Appendix 11 (Effect of Harmonic Currents on 3 Phase Systems) and Appendix 12 (Voltage Drop in Consumers’ Installations) have been moved to Appendix 4.
Appendices 11 and 12 have been left blank for future use.
B
Legal Relationship and General Requirements of BS 7671:2008 Amd No. 1:2011
Introduction
It is important to recognize that, for electrical designers and installers, there are legal responsibilities that must be both known and implemented whilst carrying out electrical installation or electrical design work. This chapter provides information and guidance on key UK legalisation relevant to electrical installations. It also provides guidance on some contractual obligations relating to design and installation.
This chapter is neither a full legal guide nor a contractual guide to requirements, but provides a short overview of the subject.
The chapter finishes with notes on the assessment of general characteristics, from the requirements of Part 3 in BS 7671:2008.
B 1 Legal Requirements and Relationship
B 1.1 Key Legal UK Legislation
Legislation can be in the form of an Act of Parliament (e.g. The Health & Safety at Work Act 1974) or a Statutory Instrument (e.g. The Electricity at Work Regulations 1989). Acts are primary legislation and Statutory Instruments are secondary legislation made under a specific Act. In the case of the Electricity at Work Regulations, these were made under the Health & Safety at Work Act. Failing to comply with requirements of an Act of Parliament or a Statutory Instrument is a breach of criminal law and may result in a prosecution.
The following legislation is considered key and relevant to the electrical technical aspects of electrical designs and electrical installations:
B 1.2 The Electricity at Work Regulations 1989 (EWR 1989)
The EWR 1989 is one of the most important pieces of legislation that an electrical designer or electrical contractor must be familiar with. You should know the content of this document as well as knowing of its existence.
The EWR 1989 cover the safety to people, including employees, involved in all aspects of electrical and electronic systems in the UK. This includes self-employed electricians working in domestic installations; all ‘electrical personnel’ in commercial installations and construction sites; and (for commercial installations) the end users. It also includes any person undertaking any work activity on or near electrical equipment.
All electrical equipment and systems are encompassed by the legislation, from a battery to the National Super Grid at 400 kV. The legislation covers design, operation, isolation, maintenance, workspace and lighting of equipment. There are regulations on precautions for working on equipment made dead and work on, or near, live conductors. There are also regulations for persons undertaking work to be competent, in order to prevent danger and injury.
Compliance with the EWR 1989 is therefore a fundamental requirement for any organization and it is recommended that organizations have in place a system of training, to ensure compliance with the regulations. Guidance on the EWR is available from the Health & Safety Executive (publication HS(R) 25 – Memorandum of Guidance on the Electricity at Work Regulations 1989), It is recommended that organizations purchase this and implement the guidance provided; it contains the text of the Act as well as HSE guidance on how to achieve the statutory requirements.
The publication consists of 50 pages and can be purchased or freely downloaded from quoting the following reference:
HS(R)25 Memorandum of Guidance on the Electricity at Work Regulations 1989),
ISBN 9780717662289
As well as having a copy of HS(R) 25, organizations must provide adequate training for all staff who work on or near electrical installations.
To supplement this, a dead working policy should be formalized, together with a live working policy for those contractors who carry out live work.
In respect to the ‘making dead’ or ‘live working’ aspects of EWR 1989, the following document is also very useful; if not essential:
HSG 85 Electricity at Work – Safe Working Practices
ISBN 0717621642
This document provides guidance on the policy and procedures for safe working practices. It includes guidance on the following:
B 1.3 The Electricity Safety, Quality and Continuity Regulations 2002 (As Amended)
These statutory regulations are primarily intended for Distribution Network Operators (DNOs), setting statutory limits for voltage and frequency.
The regulations state that PME supplies cannot be used to provide installations supplying caravans or boats. Also, DNOs can take the option not to supply an earth to installations that they feel would be inappropriate. This will possibly be the case on some farms, building sites and petrol filling stations.
For all installations, DNOs will have to take a view on the safety of an installation and will use BS 7671:2008 for this. If the DNO feels that an installation is unsafe, they can refuse to provide a supply or, if connected, disconnect the supply.
B 1.4 The Electricity Act 1984 (As Amended)
This Act is primarily aimed at Distribution Network Operators (DNOs) and (more recently) Meter Operators. However, there is a relevant point for installation designers and contractors to note: the Act gives the DNO or Meter Operator the right to position intakes where they see fit and where they feel appropriate for a given installation.
B 1.5 The Building Act 1984, The Building Regulations and Part P
The Building Act 1984 refers only to England & Wales. As mentioned earlier the requirements for Scotland are not detailed in this publication. This book does not cover all the technical requirements relating to the Building Regulations, but there are numerous guides and books on this subject, including one produced by the ECA and the NICEIC.
However, Part P of the Building Regulations (electrical safety within dwellings) is summarized below:
Legal Standing of Part P
The Building Regulations 2010 are made under the main Act of Parliament, the Building Act 1984. The Building Act is the primary legislation and refers to the Building Regulations 2010, with its various parts on structure, means of escape, spread of fire, ventilation, heat loss and, of course, electrical safety.
The Building Regulations 2010 are statutory and a breach of the regulations in itself is an offence under criminal law and may lead to prosecution.
For guidance on ways of complying with the individual parts of the Building Regulations, the DCLG (Department for Communities and Local Government) produce ‘Approved Documents’ on each part. It is important to recognize that the Approved Documents themselves are not statutory. This is demonstrated in Figure below:
The wording of the Statutory Instrument and hence the legal requirement of Part P is given in Table .
Requirement | Limits on Application |
PART P ELECTRICAL SAFETY
Design and installation | |
P1 Reasonable provision shall be made in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installations from fire or injury. | The requirements of this Part apply only to electrical installations that are intended to operate at low or extra-low voltage and are
a) in or attached to a dwelling; b) in the common parts of a building serving one or more dwellings, but excluding power supplies to lifts; c) in a building that receives its electricity from a source located within or shared with a dwelling; and d) in a garden or in or on land associated with a building where the electricity is from a source located within or shared with a dwelling. |
B 1.6 The Electromagnetic Compatibility Regulations 2006
Information on EMC and duties under the EMC directive and BS 7671:2008 is provided in Chapter D, Section D 4.
B 1.7 Tort and Negligence
This section is included to provide an introduction to this common law duty.
Tort
The English legal system recognizes two forms of ‘wrongs’. The first is what we call a ‘criminal act’ and may be punished by a fine, imprisonment or both. Commonly we think of murder, but this stemmed from an infringement of societies’ moral code, i.e. it was morally wrong to deprive someone of their life. These moral codes were identified and legislated for, initially by the overlords, then kings and ultimately by Parliament. The Health and Safety at Work Act (1974) is Parliament enacted law and, as such, creates a criminal obligation upon any transgressor.
The second is called ‘Civil’ or ‘Common’ law, colloquially known as ‘Judge made law’, because the rules and principals have been created in the courts of the land, enshrined by what is termed ‘the law of precedent’: that is, unless overturned by a superior court, the ruling establishes the law and binds judges in any subsequent cases. The Civil law is concerned with providing restitution of rights, obligations or finances in the event of some form of dispute, termed a breach.
Civil law governs both the circumstances where there is an intention to form a relationship, by creation of a legally binding agreement (the Law of Contract) where a relationship may exist without a contract being present. We call this the Law of Tort. Tort may thus be considered liability where there is no contract.
Torts include negligence, nuisance, defamation and trespass to name but a few. It is possible to owe a duty in both tort and criminal law. However, if an action is successfully pursued in a criminal court, the ‘beyond reasonable doubt’ burden of proof is considerably higher than the civil determination of ‘viewed against the balance of probabilities’. This means that the civil liability has been established. It is the function of the Criminal Compensation Board to establish the level of civil damages due to a ‘common’ infringement of rights, having established a criminal liability.
In Tort there is a need to establish a relationship. The landmark case is Donoghue v Stevenson (1932), wherein a friend of Donoghue purchased Donoghue a bottle of ginger beer, found to contain a partially decomposed snail. She successfully established that the manufacturer owed her a ‘duty of care’, under the tort of negligence. It was judged that ‘she’ was in a relationship, even though ‘she’ had no direct contractual relationship with the manufacturer. This ‘neighbour’ principle is important, as it establishes whether or not a duty of care is owed. The question follows: Who is my neighbour? Well the answer is, anyone who it is foreseeable, or likely, to be affected by your actions.
As you can see, liability in Tort is therefore very wide and the rules governing its implementation are extremely complex. Seventy years on, the courts are still grappling with the principals and extent of this law.
To some extent this is why Collateral Warranties are called for, because rather than rely on the Tort of negligence, parties in a Collateral Warranty Agreement can instead sue for a breach of contract. The level of damages may be similar or higher and it is easier to prove a breach under contract law. We ignore ‘pure economic loss’ and the newly enacted Rights Of Third Parties Act.
Negligence
If you negligently design a system or provide a service, which causes death, personal injury or damage to property, then you can be held liable for these losses under the Tort of negligence. Making a mistake, or getting something wrong is not being negligent. Being negligent is where you are found to have performed at a level less than would have been expected by a ‘reasonable man’, whilst undertaking a task for which you have declared yourself competent. For example, if you declare yourself as being competent to design a lighting system, offer advice concerning that system (upon which others rely) and the installation is subsequently found to be deficient, you may be held financially liable. This is irrespective of any payments made. It is for this reason that designers and contractors of services are strongly advised to insure themselves with Professional Indemnity Insurance cover.
B 2 The Role of Standards
Definition of Standards
Standards, including international, European and British standards, are documents to bring about simplification, interchangeability, terminology, methodology, specification or codified practice.
A standard is defined as:
‘a document established by consumers and approved by a recognised body that provides for common and repeated use, rules, guidelines or characterisation for activities or their results, aimed at the achievement of the optimum degree in a given context’.
(This was taken from IEC Guide 2, 1996)
Standards are (or should be) written by industry and by consensus, where consensus is defined as:
‘General agreement, characterised by the absence of sustained opposition or substantial opposition by any important part of the concerned interests and by a process that involves seeking to take into account the views of all parties concerned and to reconcile any conflicting arguments’.
Legal Standing of Standards
Standards are described or implicated by statute. Standards are voluntary codes of rules and are not law, nor are they legally enforceable. Indeed, individuals may take a view to ignore a particular standard. However, some standards are boosted to an elevated status by being referred to either directly or indirectly in statutes. Depending upon the wording, this can give the standards themselves a quasi-legal status. Again, though, there is a caveat. A good way to explain this further is to look at how BS 7671 is referred to in some legal documents.
BS 7671 and the Electricity at Work Regulations 1989 (EWR)
It is important to recognize that the wording of the EWR makes no mention of BS 7671. The HSE’s Memorandum of Guidance (HS(R) 25), states that:
BS 7671 is a code of practice which is widely recognised and accepted in the UK and compliance with it is likely to achieve compliance with relevant aspects of the 1989 (EWR) Regulations.
BS 7671 and Part P of the Building Regulations 2000
In a similar fashion, BS 7671 is not mentioned in the primary legislation, which simply states ‘the installation shall be designed and installed in order to protect persons from fire or injury.’
It is Approved Document P (which itself is guidance) that mentions BS 7671.
This states ‘in the Secretary of State’s view, the (Part P) requirements will be met by adherence to the “Fundamental Principles” for achieving safety given in BS 7671:2001 Chapter 13’.
This will need updating to read correctly for BS 7671:2008.
Standards Implied or Prescribed by Contract
Standards are often prescribed by a contract on a definite item being stated or by a general contract term similar to ‘shall comply with all relevant codes and standards’.
Assuming the standard is relevant and it is listed, then compliance with the standard becomes binding under the UK Law of Contract.
B 3 Part 3 of BS 7671:2008 – Assessment of General Characteristics
Part 3 of BS 7671, sets requirements for an overall assessment of an electrical installation. It is intended that the requirements of Part 3 be considered prior to the design of an installation, in compliance with other Parts of BS 7671. This works for some of the regulations in Part 3, but some are repetitive of the general requirements given in Parts 4 or 5.
The requirements are summarized in Table and are summarized in just five paragraphs. The regulation numbers have been omitted for clarity and due to the fact that the requirements are so general.
Requirement of Regulations | Notes and advice |
The installation shall be assessed for purpose, external influence, compatibility, maintainability, continuity of service and recognised safety services. | |
The characteristics of voltage, current, frequency, prospective fault current, earth fault loop impedance (ELI), maximum demand and protective device at the origin shall be determined. | This can be done by inspection, by enquiry, measurement, calculation and applies to all sources of supply. Safety supplies shall be assessed separately and the requirements of these are in Chapter 56 of BS 7671 (see Chapter D). |
Installations shall be suitably divided up to avoid danger, minimise inconvenience in the event of a fault, facilitate safe inspection, testing and maintenance; take account of the hazards that might arise from the failure of a single circuit, reduce the possibility of unwanted tripping of RCDs, mitigate the effects of electromagnetic disturbance, and ensure effective isolation.
Continuity of supply for the intended use and life of the installation shall be considered. | These requirements are discussed with recommendations made in Chapter C. |
Final circuits shall be connected to separate protective devices at distribution boards. | |
Compatibility and EMC shall be considered. | See Chapters C and D. |