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17th Edition IEE Wiring Regulations PDF

133 Pages·2011·4.5 MB·English
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17th Edition IEE Wiring Regulations: Design and Verification of Electrical Installations By the same author 17th Edition IEE Wiring Regulations: Inspection, Testing and Certification, ISBN 978-0-0809-6610-6 17th Edition IEE Wiring Regulations: Explained and Illustrated, ISBN 978-0-7506-8720-1 Electric Wiring: Domestic, ISBN 978-0-7506-8735-5 PAT: Portable Appliance Testing, ISBN 978-0-0809-6919-0 Wiring Systems and Fault Finding, ISBN 978-0-7506-8734-8 Electrical Installation Work, ISBN 978-0-7506-8733-1 17th Edition IEE Wiring Regulations: Design and Verification of Electrical Installations Seventh Edition Brian Scaddan, IEng, MIET AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK OXFORD • PARIS • SAN DIEGO • SAN FRANCISCO SINGAPORE • SYDNEY • TOKYO Newnes is an imprint of Elsevier Newnes is an imprint of Elsevier The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK 225 Wyman Street, Waltham, MA 02451, USA First edition 1995 Second edition 1999 Third edition 2001 Fourth edition 2002 Fifth edition 2005 Sixth edition 2008 Seventh edition 2011 Copyright © 2011, Brian Scaddan. Published by Elsevier Ltd. All rights reserved The right of Brian Scaddan to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988 No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the publisher Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone (+44) (0) 1865 843830; fax (+44) (0) 1865 853333; email: permissions @elsevier.com. Alternatively you can submit your request online by visiting the Elsevier web site at http://elsevier.com/locate/permissions, and selecting Obtaining permission to use Elsevier material Notice No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. Because of rapid advances in the medical sciences, in particular, independent verification of diagnoses and drug dosages should be made British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is availabe from the Library of Congress ISBN: 978-0-08-096914-5 Printed and bound in Italy 11 12 13 14 15 10 9 8 7 6 5 4 3 2 1 For information on all Newnes publications visit our web site at books.elsevier.com In memory of Ted Stocks A friend and colleague This page intentionally left blank Contents PREFACE �������������������������������������������������������������������������������������������������������ix CHAPTER 1 Design ������������������������������������������������������������������������������������ 1 Assessment of General Characteristics ����������������������������������������������������������� 2 Protection for Safety ��������������������������������������������������������������������������������������� 7 Protection Against Electric Shock ������������������������������������������������������������������� 7 Protection Against Thermal Effects (IEE Regulations Chapter 42) ������������������ 15 Protection Against Overcurrent ��������������������������������������������������������������������� 15 Protection Against Overload �������������������������������������������������������������������������� 16 Protection Against Fault Current ������������������������������������������������������������������� 18 Protection Against Undervoltage (IEE Regulations Section 445) �������������������� 22 Protection Against Overvoltage (IEE Regulations Sections 442 and 443) �������� 22 Isolation and Switching ��������������������������������������������������������������������������������� 22 Design Calculations �������������������������������������������������������������������������������������� 26 CHAPTER 2 Inspection and Testing ����������������������������������������������������������� 53 Initial Verification ������������������������������������������������������������������������������������������ 53 Inspection ���������������������������������������������������������������������������������������������������� 54 Testing ��������������������������������������������������������������������������������������������������������� 54 Approved Test Lamps and Indicators ������������������������������������������������������������ 56 Calibration, Zeroing/Nulling and Care of Instruments ������������������������������������ 57 The Tests ����������������������������������������������������������������������������������������������������� 58 Continuity of Protective Conductors �������������������������������������������������������������� 59 Continuity of Ring Final Circuit Conductors ��������������������������������������������������� 60 Insulation Resistance ����������������������������������������������������������������������������������� 67 Polarity �������������������������������������������������������������������������������������������������������� 70 Ring Final Circuits ���������������������������������������������������������������������������������������� 70 Radial Circuits ���������������������������������������������������������������������������������������������� 70 Earth Electrode Resistance ��������������������������������������������������������������������������� 72 External Loop Impedance Ze ������������������������������������������������������������������������� 74 Earth Fault Loop Impedance Zs �������������������������������������������������������������������� 75 Additional Protection ������������������������������������������������������������������������������������ 75 vii CHAPTER 3 Special Locations IEE Regulations Part 7 ������������������������������� 83 Introduction ������������������������������������������������������������������������������������������������� 83 BS 7671 Section 701: Bathrooms, etc� ��������������������������������������������������������� 84 BS 7671 Section 702: Swimming Pools �������������������������������������������������������� 87 BS 7671 Section 703: Hot Air Saunas ���������������������������������������������������������� 89 BS 7671 Section 704: Construction Sites ������������������������������������������������������ 91 BS 7671 Section 705: Agricultural and Horticultural Locations ���������������������� 92 BS 7671 Section 706: Conductive Locations with Restrictive Movement �������� 94 BS 7671 Section 708: Caravan and Camping Parks �������������������������������������� 94 BS 7671 Section 709: Marinas ��������������������������������������������������������������������� 95 BS 7671 Section 710: Medical Locations ������������������������������������������������������ 96 BS 7671 Section 711: Exhibitions, Shows and Stands ����������������������������������� 97 BS 7671 Section 712: Solar Photovoltaic (PV) Supply Systems ��������������������� 99 BS 7671 Section 717: Mobile or Transportable Units ������������������������������������ 99 BS 7671 Section 721: Caravans and Motor Caravans ����������������������������������� 99 BS 7671 Section 729: Operating and Maintenance Gangways �������������������� 101 BS 7671 Section 740: Amusement Devices, Fairgrounds, Circuses, etc� ����� 101 BS 7671 Section 753: Floor and Ceiling Heating Systems ��������������������������� 102 APPENDIX 1 BS 7671 Appendices ��������������������������������������������������������� 105 APPENDIX 2 Sample Questions �������������������������������������������������������������� 107 APPENDIX 3 Suggested Solutions to Sample Questions ��������������������������� 113 INDEX �������������������������������������������������������������������������������������������������������� 121 Contents viii Preface There are many electrical operatives who, quite innocently I am sure, select wiring systems based on the old adage of ‘that’s the way it’s always been done’ or ‘we always use that size of cable for that circuit’, etc. Unfor- tunately this approach, except for a few standard circuits, is quite wrong. Each wiring system should be designed to be fit for purpose and involves more than arbitrary choices. The intention of this book is to illustrate the correct procedure for basic design of installations from initial assessment to final commissioning. It will also be of use to candidates studying for a C&G 2391-20 Design qualification. This edition has been revised to serve as an accompaniment to the new City & Guilds scheme and has been brought fully up-to-date with the 17th Edition IEE Wiring Regulations. Brian Scaddan, April 2011 ix This page intentionally left blank IEE Wiring Regulations. DOI: 10.1016/B978-0-08-096914-5.10001-9 1 © 2011 Brian Scaddan. Published by Elsevier Ltd. All rights reserved. CHAPTER 1 Design Important terms/topics covered in this chapter: ▪ Assessment of general characteristics ▪ Basic protection ▪ Fault protection ▪ IP and IK codes ▪ The earth fault loop path ▪ Supplementary equipotential bonding ▪ Overcurrent ▪ Let-through-energy ▪ Discrimination ▪ Undervoltage ▪ Overvoltage ▪ Isolation and switching ▪ Design current ▪ Diversity ▪ Nominal rating of protection ▪ Rating factors ▪ Current carrying capacity of conductors ▪ Voltage drop ▪ Shock risk and thermal constraints. At the end of this chapter the reader should, ▪ understand the need to assess all relevant characteristics of the installation, ▪ have reinforced their knowledge of Basic and Fault protection and how such protection is achieved, ▪ understand how ‘let-through-energy’ can cause damage to cables, ▪ be able to distinguish between ‘Isolation’ and ‘Switching’, ▪ be able to determine suitable wiring systems for particular applications, 2 IEE Wiring Regulations ▪ be able to carry out basic design calculations to determine cable sizes, ▪ recognize various types of installation diagram. Any design to the 17th Edition of the IEE Wiring Regulations BS 7671 must be primarily concerned with the safety of persons, property and livestock. All other considerations such as operation, maintenance, aes- thetics, etc., while forming an essential part of the design, should never compromise the safety of the installation. The selection of appropriate systems and associated equipment and accessories is an integral part of the design procedure, and as such can- not be addressed in isolation. For example, the choice of a particular type of protective device may have a considerable effect on the calculation of cable size or shock risk, or the integrity of conductor insulation under fault conditions. Perhaps the most difficult installations to design are those involving addi- tions and/or alterations to existing systems, especially where no original details are available, and those where there is a change of usage or a refur- bishment of a premises, together with a requirement to utilize as much of the existing wiring system as possible. So, let us investigate those parts of the Wiring Regulations that need to be considered in the early stages of the design procedure. ASSESSMENT OF GENERAL CHARACTERISTICS Regardless of whether the installation is a whole one, an addition, or an alteration, there will always be certain design criteria to be considered before calculations are carried out. Part 3 of the 17th Edition, ‘Assess- ment of General Characteristics’, indicates six main headings under which these considerations should be addressed. These are: 1. Purpose, supplies and structure 2. External influences 3. Compatibility 3 Design 4. Maintainability 5. Recognized safety services 6. Assessment of continuity of service. Let us look at these headings in a little more detail. Purpose, supplies and structure ▪ For a new design, will the installation be suitable for its intended purpose? ▪ For a change of usage, is the installation being used for its intended purpose? ▪ If not, can it be used safely and effectively for any other purpose? ▪ Has the maximum demand been evaluated? ▪ Can diversity be taken into account? ▪ Are the supply and earthing characteristics suitable? ▪ Are the methods for protection for safety appropriate? ▪ If standby or safety supplies are used, are they reliable? ▪ Are the installation circuits arranged to avoid danger and facilitate safe operation? External influences Appendix 5 of the IEE Regulations classifies external influences which may affect an installation. This classification is divided into three sec- tions, the environment (A), how that environment is utilized (B) and construction of buildings (C). The nature of any influence within each section is also represented by a number. Table 1.1 gives examples of the classification. With external influences included on drawings and in specifications, installations and materials used can be designed accordingly. Table 1.1 Examples of Classifications of External Influences Environment Utilization Building Water Capability Materials AD6 Waves BA3 Handicapped CA1 Non-combustible 4 IEE Wiring Regulations Compatibility It is of great importance to ensure that damage to, or mal-operation of, equipment cannot be caused by harmful effects generated by other equip- ment even under normal working conditions. For example, MIMS cable should not be used in conjunction with discharge lighting, as the insula- tion can break down when subjected to the high starting voltages; the operation of residual current devices (RCDs) may be impaired by the mag- netic fields of other equipment; computers, PLCs, etc. may be affected by normal earth leakage currents from other circuits. Maintainability The Electricity at Work Regulations 1989 require every system to be maintained such as to prevent danger; consequently, all installations require maintaining, some more than others, and due account of the fre- quency and quality of maintenance must be taken at the design stage. It is usually the industrial installations that are mostly affected by the need for regular maintenance, and hence, consultation with those responsible for the work is essential in order to ensure that all testing, maintenance and repair can be effectively and safely carried out. The following exam- ple may serve to illustrate an approach to consideration of design criteria with regard to a change of usage. Example 1.1 A vacant two-storey light industrial workshop, 12 years old, is to be taken over and used as a Scout/Guide HQ. New shower facilities are to be pro- vided. The supply is three-phase 400/230V and the earthing system is TN-S. The existing electrical installation on both floors comprises steel trunk- ing at a height of 2.5m around all perimeter walls, with steel conduit, to all socket outlets and switches (metal-clad), to numerous isolators and switch-fuses once used to control single- and three-phase machinery, and to the lighting which comprises fluorescent luminaires suspended by chains from the ceilings. The ground floor is to be used as the main

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