Guide to the IET Wiring Regulations E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 313

Veröffentlichungsjahr: 2012

Beschreibung

This authoritative, best-selling guide has been extensively updated with the new technical requirements of the IET Wiring Regulations (BS 7671: 2008) Amendment No. 1:2011, also known as the IET Wiring Regulations 17^th Edition. With clear description, it provides a practical interpretation of the amended regulations – effective January 2012 – offers real solutions to the problems that can occur in practice.

This revised edition features:

• new material on hot topics such as electromagnetic compatibility (EMC), harmonics, surge protective devices, and new special locations including medical locations, and operative or maintenance gangways;
• highlights the changes that have been made in this latest Amendment and their impact in practice;
• examples of how to comply with the Wiring Regulations;
• fully-integrated colour including sixty brand new colour illustrations, twenty tables and new high-quality photographs.

This essential guide retains its handy format, ideal for practicing electricians, trainee electricians and apprentices to carry with them for quick reference. It is a valuable resource for all users of BS 7671 who want to understand the background to the Regulations; electrical engineers and technicians, installation and design engineers, consulting and building services engineers, also dedicated inspectors and testers.

Leseprobe

Table of Contents

Cover

Title page

Copyright page

Foreword by Giuliano Digilio

Head of Technical Services, Electrical Contractors’ Association (ECA)

Preface

Acknowledgements

A: BS 7671:2008 Amd No. 1:2011 Requirements for Electrical Installations – Introduction and Overview

A 1 Introduction to BS 7671:2008

A 2 Plan and layout of BS 7671:2008

A 3 Overview of major changes

A 4 Amendment No. 1:2011

B: Legal Relationship and General Requirements of BS 7671:2008 Amd No. 1:2011

Introduction

B 1 Legal requirements and relationship

B 2 The role of Standards

B 3 Part 3 of BS 7671:2008 – assessment of general characteristics

C: Circuitry and Related Parts of BS 7671:2008 Amd No. 1:2011

C 1 Introduction

C 2 Design procedure overview

C 3 Load assessment

C 4 Circuitry design

C 5 Sub-mains

C 6 Discrimination co-ordination

C 7 Parallel cables

C 8 Harmonics

C 9 Standard final circuit designs

C 10 RCDs and circuitry

C 11 Ring and radial final circuits

D: Selection and Erection – Equipment

D 1 Introduction and fundamentals

D 2 Compliance with Standards

D 3 Identification of conductors – introduction

D 4 Protection against voltage and electromagnetic disturbance

D 5 Wiring systems

D 6 Circuit breakers

D 7 Residual current devices

D 8 Other equipment

D 9 Generating sets

D 10 Rotating machines

D 11 Plugs and socket-outlets

D 12 Electrode water heaters and electrode boilers

D 13 Heating conductors

D 14 Lighting and luminaires

D 15 Safety services

D 16 Ingress protection (IP), external influences

E: Earthing and Bonding

E 1 Introduction

E 2 Earthing arrangements

E 3 General requirements of earthing and bonding

E 4 Protective conductors

E 5 Armoured cables as protective conductors

E 6 Protective bonding

E 7 High earth leakage installations

F: Inspection Testing and Certification (Part 6)

F 1 Introduction

F 2 Visual inspection

F 3 Testing

F 4 Certification paperwork

G: Special Locations

G 1 Introduction purpose and principles

G 2 Locations containing a bath or shower (701)

G 3 Swimming pools and other basins (702)

G 4 Agricultural and horticultural premises (705)

G 5 Caravan parks and camping parks (708)

G 6 Medical locations (710)

G 7 Exhibitions, shows and stands (711)

G 8 Solar photovoltaic (PV) power supply systems (712)

G 9 Mobile or transportable units (717)

G 10 Floor and ceiling heating systems (753)

Appendices

Appendix 1 – Standards and bibliography

Appendix 2 – Popular cables: current rating tables from BS 7671:2008 Appendix 4

Appendix 3 – Limiting earth fault loop impedance tables from BS 7671:2008

Appendix 4 – Cable data resistance, impedance and ‘R1 + R2’ values

Appendix 5 – Fuse I2t characteristics

Index

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 A 1.1.

Figure A 1.1 Installation standards at International, European and National levels

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 1.1.

Table A 1.1 CENELEC HD 60384 and IEC 6-364 documents used in BS 7671:2008.

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:

PartContents1Scope, Object and Fundamental Principles2Definitions3Assessment of General Characteristics4Protection For Safety5Selection and Erection of Equipment6Inspection and Testing7Special 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 A 3.1). 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’.

Figure A 3.1 Basic Protection and Fault Protection

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.