Practical Grounding, Bonding, Shielding and Surge Protection ii Contents Other titles in the series Practical Data Acquisition for Instrumentation and Control Systems (John Park, Steve Mackay) Practical Data Communications for Instrumentation and Control (Steve Mackay, Edwin Wright, John Park) Practical Digital Signal Processing for Engineers and Technicians (Edmund Lai) Practical Electrical Network Automation and Communication Systems (Cobus Strauss) Practical Embedded Controllers (John Park) Practical Fiber Optics (David Bailey, Edwin Wright) Practical Industrial Data Networks: Design, Installation and Troubleshooting (Steve Mackay, Edwin Wright, John Park, Deon Reynders) Practical Industrial Safety, Risk Assessment and Shutdown Systems for Instrumentation and Control (Dave Macdonald) Practical Modern SCADA Protocols: DNP3, 60870.5 and Related Systems (Gordon Clarke, Deon Reynders) Practical Radio Engineering and Telemetry for Industry (David Bailey) Practical SCADA for Industry (David Bailey, Edwin Wright) Practical TCP/IP and Ethernet Networking (Deon Reynders, Edwin Wright) Practical Variable Speed Drives and Power Electronics (Malcolm Barnes) Practical Centrifugal Pumps (Paresh Girdhar and Octo Moniz) Practical Electrical Equipment and Installations in Hazardous Areas (Geoffrey Bottrill and G. Vijayaraghavan) Practical E-Manufacturing and Supply Chain Management (Gerhard Greef and Ranjan Ghoshal) Practical Hazops, Trips and Alarms (David Macdonald) Practical Industrial Data Communications: Best Practice Techniques (Deon Reynders, Steve Mackay and Edwin Wright) Practical Machinery Safety (David Macdonald) Practical Machinery Vibration Analysis and Predictive Maintenance (Cornelius Scheffer and Paresh Girdhar) Practical Power Distribution for Industry (Jan de Kock and Cobus Strauss) Practical Process Control for Engineers and Technicians (Wolfgang Altmann) Practical Telecommunications and Wireless Communications (Edwin Wright and Deon Reynders) Practical Troubleshooting Electrical Equipment (Mark Brown, Jawahar Rawtani and Dinesh Patil) Contents iii Practical Grounding, Bonding, Shielding and Surge Protection G. Vijayaraghavan, B.Eng (Hons) Consulting Engineer, Chennai, India Mark Brown, Pr.Eng, DipEE, B.Sc (Elec.Eng), Senior Staff Engineer, IDC Technologies, Perth, Australia. Malcolm Barnes, CPEng, BSc (ElecEng), MSEE, Alliance Automation, Perth, Western Australia Series editor: Steve Mackay AMSTERDAM • BOSTON • HEIDELBERG • LONDON NEW YORK • OXFORD • PARIS • SAN DIEGO SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Newnes is an imprint of Elsevier iv Contents Newnes An imprint of Elsevier Linacre House, Jordan Hill, Oxford OX2 8DP 200 Wheeler Road, Burlington, MA 01803 First published 2004 Copyright © 2004, IDC Technologies. All rights reserved No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England WIT 4LP. Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publisher Permissions may be sought directly from Elsevier’s Science and Technology Rights Department in Oxford, UK: phone: (+44) (0) 1865 843830; fax: (+44) (0) 1865 853333; e-mail: permissions@elsevier.co.uk. You may also complete your request on-line via the Elsevier homepage (http://www.elsevier.com), by selecting ‘Customer Support’ and then ‘Obtaining Permissions’ British Library Cataloguing in Publication Data Vijayaraghavan, G. Practical grounding, bonding, shielding and surge protection. – (Practical professional) 1. Electric apparatus and appliances – Protection 2. Electric currents – Grounding I. Title 621. 3’17 Library of Congress Cataloguing in Publication Data A catalogue record for this book is available from the Library of Congress ISBN 0 7506 6399 5 Typeset and edited by Integra Software Services Pvt. Ltd, Pondicherry, India www.integra-india.com Printed and bound in The Netherlands Working together to grow libraries in developing countries www.elsevier.com | www.bookaid.org | www.sabre.org For information on all Newnes publications visit our website at www.newnespress.com Contents v Contents Preface ix 1 Introduction and basics .1 1.1 Introduction .1 1.2 Basics of grounding 2 1.3 Bonding 4 1.4 Lightning and its effect on electrical systems 4 1.5 Static charges and the need for bonding 5 1.6 Ground electrodes and factors affecting their efficacy 6 1.7 Noise in signaling circuits and protective measures such as shielding .8 1.8 Surge protection of electronic equipment .9 1.9 UPS systems and their role in power quality improvement .10 1.10 Case studies .11 1.11 Importance of local codes .11 1.12 Summary 11 2 Grounding of power supply system neutral 13 2.1 Introduction .13 2.2 Ungrounded systems 15 2.3 Solidly grounded systems .16 2.4 Impedance grounding using neutral reactor .18 2.5 Resonant grounding using neutral reactor 18 2.6 Impedance grounding through neutral resistance .19 2.7 Point of grounding 20 2.8 Other challenges 21 2.9 Summary 23 3 Equipment grounding 24 3.1 Introduction .24 3.2 Shock hazard .24 3.3 Grounding of equipment .27 3.4 Operation of protective devices 28 3.5 Thermal capability 29 3.6 Touch Potential during ground faults 30 3.7 Induced voltage problem 30 3.8 Mitigation by multiple ground connection 31 3.9 Mitigation by reduction of conductor spacing 31 vi Contents 3.10 EMI suppression 32 3.11 Metal enclosures for grounding conductors . 32 3.12 Grounding connections for surge protection equipment . 34 3.13 Sensing of ground faults 34 3.14 Equipotential bonding 35 3.15 Summary . 37 4 Lightning, its effect on buildings and electrical systems and protection against lightning 38 4.1 Introduction 38 4.2 Incidence of lightning . 41 4.3 Probability of lightning strike 45 4.4 Method of lightning protection 47 4.5 Planning for lightning protection . 50 4.6 Improvements to lightning protection . 51 4.7 Factors governing decision whether or not to protect . 52 4.8 Effect of lightning strike on electrical lines 53 4.9 Summary . 54 5 Static electricity and protection . 55 5.1 Introduction 55 5.2 What is static electricity? 55 5.3 Generation of charge . 56 5.4 Some common examples of static buildup . 56 5.5 Energy of spark and its ignition capability 57 5.6 Dangers of static electricity buildup 58 5.7 Control of static electricity 58 5.8 Assessment of static risks and planning prevention . 61 5.9 Summary . 61 6 Ground electrode system 62 6.1 Introduction 62 6.2 Grounding electrodes . 62 6.3 Soil resistance . 63 6.4 Measurement of soil resistivity . 64 6.5 Resistance of a single rod electrode 68 6.6 Current-carrying capacity of an electrode 70 6.7 Use of multiple ground rods in parallel . 71 6.8 Measurement of ground resistance of an electrode . 71 6.9 Concrete-encased electrodes 73 6.10 Corrosion problems in electrical grounding systems 75 6.11 Maintenance of grounding system . 76 6.12 Chemical electrodes 76 6.13 Summary . 78 7 Surge protection of electronic equipment 79 7.1 Introduction 79 7.2 What is a surge? 79 Contents vii 7.3 Bonding of different ground systems as a means of surge proofing .80 7.4 Surges and surge protection .82 7.5 Principle of surge protection .85 7.6 Surge protection of electronic equipment .86 7.7 Achieving graded surge protection .88 7.8 Positioning and selection of lightning/surge arrestor .89 7.9 A practical view of surge protection for sensitive equipment .92 7.10 Summary 101 8 Electrical noise and mitigation .102 8.1 Introduction .102 8.2 Definition of electrical noise and measures for noise reduction 102 8.3 How are sensitive circuits affected by noise? .105 8.4 Frequency analysis of noise .106 8.5 Categories of noise .109 8.6 Disturbances from other equipment in the same distribution system 110 8.7 Earth loop as a cause of noise .111 8.8 The ways in which noise can enter a signal cable and its control .113 8.9 More about shielding .117 8.10 Shielded isolation transformer 121 8.11 Avoidance of earth loop 123 8.12 Use of insulated ground (IG) receptacle 125 8.13 Zero signal reference grid and signal transport ground plane .126 8.14 Harmonics in electrical systems 128 8.15 Summary 131 9 UPS systems and their grounding practices 132 9.1 Introduction .132 9.2 Power quality issues .132 9.3 Definitions of abnormal voltage conditions .134 9.4 Susceptibility and measures to handle voltage abnormalities .137 9.5 Regulating transformer .137 9.6 Standby sources .138 9.7 Electromechanical UPS systems 142 9.8 Solid-state UPS systems 144 9.9 Multiple units for redundancy 146 9.10 Considerations in selection of UPS systems for ADP facilities 147 9.11 Grounding issues in static UPS configurations .149 9.12 UPS configurations and recommended grounding practices 149 9.13 Summary 153 10 Case studies 154 10.1 Introduction .154 10.2 Case study 1 154 10.3 Case study 2 155 10.4 Case study 3 158 viii Contents 10.5 Case study 4 159 10.6 Case study 5 160 10.7 Case study 6 160 10.8 Case study 7 162 10.9 Case study 8 162 Appendix A: Grounding regulations from various national codes 165 Appendix B: IEE system classification based on grounding practices . 182 Appendix C: IEEE exposure classifications . 191 Appendix D: Glossary of terms related to grounding . 193 Appendix E: Steps to ensure effective substation grounding . 201 Appendix F: Course exercises 207 Appendix G: Answer schemes 210 Appendix H: Group activities . 221 Index . 233 Preface Few topics generate as much controversy and argument as that of grounding and the associated topics of surge protection, shielding and lightning protection of electrical and electronic systems. Poor grounding practice can be the cause of continual and intermittent difficult-to-diagnose problems in a facility. This book looks at these issues from a fresh yet practical perspective and enables you to reduce expensive downtime on your plant and equipment to a minimum by correct application of these principles. This book is designed to demystify the subject of grounding and presents the subject in a clear, straightforward manner. Installation, testing and inspection procedures for industrial and commercial power systems will be examined in detail. Essentially the discussion in this book is broken down into grounding, shielding and surge protection for both power and electronics systems. Grounding and surge protection for Telecommunications and IT systems are examined in detail. Finally, the impact of lightning is examined and simple techniques for minimizing its impact are described. The terms grounding and earthing are understood to be interchangeable in this book but due to the larger readership the term grounding has been the preferred usage. Our apologies to our European readers for this unfortunate compromise. Typical people who will find this book useful include: • Instrumentation and Control Engineers • Consulting Engineers • Electrical Engineers • Project Engineers • Maintenance Engineers • Electrical Contractors • Safety Professionals • Consulting Engineers • Electricians • Electrical Inspectors • Power System Protection and Control Engineers • Building Service Designers • Data Systems Planners and Managers • Electrical and Instrumentation Technicians. We would hope that you will gain the following from this book: • Knowledge of the various methods of grounding electrical systems • Details of the applicable national Standards • The purposes of grounding and bonding • A list of the types of systems that cannot be grounded • Details on how to correctly shield sensitive communications cables from noise and interference • Know-how on surge and transient protection . down into grounding, shielding and surge protection for both power and electronics systems. Grounding and surge protection for Telecommunications and IT systems. controversy and argument as that of grounding and the associated topics of surge protection, shielding and lightning protection of electrical and electronic