Table Of ContentGrounding Electrical
Distribution Systems
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Grounding Electrical
Distribution Systems
Gregory P. Bierals
Electrical Design Institute, USA
River Publishers
Published 2021 by River Publishers
River Publishers
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www.riverpublishers.com
Distributed exclusively by Routledge
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605 Third Avenue, New York, NY 10017, USA
Library of Congress Cataloging-in-Publication Data
Grounding Electrical Distribution Systems / Gregory P. Bierals.
©2021 River Publishers. All rights reserved. No part of this publication may
be reproduced, stored in a retrieval systems, or transmitted in any form or by
any means, mechanical, photocopying, recording or otherwise, without prior
written permission of the publishers.
Routledge is an imprint of the Taylor & Francis Group, an informa business
ISBN 978-87-7022-617-2 (print)
ISBN 978-87-7022-616-5 (online)
ISBN 978-1-003-20730-6 (ebook master)
NEC®, NFPA 70®, NFPA 70B®, NFPA 70E® and National Electrical Code®
are registered trademarks of the National Fire Protection Association.
The IEEE Standards referenced in this book are from the Institute of Electrical
and Electronics Engineers
While every effort is made to provide dependable information, the publisher,
authors, and editors cannot be held responsible for any errors or omissions.
Contents
Introduction vii
1 Grounded and Ungrounded Systems System Grounding 1
Direct-Current Systems . . . . . . . . . . . . . . . . . . . . . . . 2
Ungrounded or Impedance Grounded Systems . . . . . . . . . . . 3
Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2 A Practical Example 29
3 The Lightning Phenomenon 33
4 The Grounding Electrode System 39
5 Bonding 47
Load-Side Bonding Jumpers . . . . . . . . . . . . . . . . . . . . 49
Bonding Metal Water Pipes and Exposed Structural Steel . . . . . 57
Bonding in Hazardous (Classified) Locations . . . . . . . . . . . . 60
Health Care Facilities . . . . . . . . . . . . . . . . . . . . . . . . 61
Swimming Pools, Fountains, and Similar Installations . . . . . . . 61
6 Ground-Fault Protection of Equipment 65
7 Overcurrent Protection-Current Limitation
Selective-Coordination 75
Electrical Safety in the Workplace NFPA 70E . . . . . . . . . . . 79
NFPA 70 E Article 100 Definitions . . . . . . . . . . . . . . . . . 81
8 Review of NEC 85
Article 250 Grounding and Bonding Review . . . . . . . . . . . . 85
Two or More Buildings Supplied by A Feeder(s) or
Branch Circuit(s) . . . . . . . . . . . . . . . . . . . . . . . 91
Grounding Electrode System and Grounding
Electrode Conductor . . . . . . . . . . . . . . . . . . . . . . 93
v
vi Contents
Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Grounding of Systems or Circuits of over 1000 volts . . . . . . . . 116
9 Special Considerations 119
Solar Photovoltaic Systems . . . . . . . . . . . . . . . . . . . . . 124
Equipment Grounding . . . . . . . . . . . . . . . . . . . . . . . . 127
Grounding Electrode System . . . . . . . . . . . . . . . . . . . . 130
Grounding and Equipotential Bonding Agricultural
Buildings (Article 547) . . . . . . . . . . . . . . . . . . . . 131
Equipment Bonding . . . . . . . . . . . . . . . . . . . . . . . . . 133
Swimming Pools. Fountains, and Similar
Installations-Grounding and Bonding . . . . . . . . . . . . . 133
Wiring Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
Equipotential Bonding . . . . . . . . . . . . . . . . . . . . . . . . 135
Article 517 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
Index 155
About the Author 157
Introduction
To begin, we will identify and analyze the definitions of terms in Article 100
of the NEC that relate to Bonding and Grounding. These terms and definitions
must be thoroughly understood before going further into our study.
And, before we address the proper bonding and grounding methods, we
will identify the AC Systems that are not required to be grounded, as well as
those that are not permitted to be grounded.
In addition, Impedance Grounded Systems will be identified and treated
in a similar way as ungrounded systems, although there are added benefits in
the use of these systems.
It has been my experience that the topics of grounding systems and
equipment are some of the most widely misunderstood subjects in the
electrical industry.
There have been so many books and publications relating to proper
bonding and grounding methods. And yet, there is still a significant amount
of misunderstanding. And so, this book is designed to clarify these issues.
Throughout this book there are references to the appropriate Sections of the
National Electrical Code. This has been done to further clarify my intention of
stressing the purpose of the NEC, that is, the practical safeguarding of persons
and property from hazards arising from the use of electricity (Section 90.1(A)).
It is my sincere desire to be of help in the proper application of installation
methods that will assure safe and reliable electrical installations.
Of course, personal safety is of paramount importance, and this can
never be compromised. But the proper means to install electrical systems
that enhance the reliability and proper operation of electrical equipment is
of equal importance. These two methods of protection go hand-in-hand, and
neither may be overlooked.
As always, I welcome your comments and suggestions in order to better
serve the electrical industry.
Sincerely,
Gregory P. Bierals
Electrical Design Institute
vii
1
Grounded and Ungrounded Systems
System Grounding
System grounding is sometimes a requirement, especially when dealing with
the most common types of premises wiring systems. For example, Section
250.20(A) and (B) relate to AC systems that must be grounded.
First, for systems operating at less than 50 volts, the following conditions
apply:
1. If the supply transformer exceeds 150 volts-to-ground
2. If the supply transformer is ungrounded
3. Where the circuit operating at less than 50 volts is installed outside as
overhead conductors
In the first case, if the primary of the transformer exceeds 150 volts-to
ground, there is a possibility that a primary-to-secondary fault would elevate
the secondary voltage to an unsafe level, which may be a hazard to people,
as well as to equipment. The secondary ground (earth) connection will limit
this voltage-rise.
This also applies to the second provision where the transformer secondary,
operating at less than 50 volts, would have a means of limiting any voltage-
rise above ground (earth) potential, due to the fact that the primary circuit has
no ground reference ('0' volts).
The third condition relates to the possibility of the exposed outside
overhead conductors making contact with higher voltage lines, or lightning
induced influences.
For AC systems of 50-1000 volts, the following conditions apply:
1. If the system is grounded and the maximum voltage-to-ground is limited
to 150 volts, such as the typical 240/120 volt single-phase system or a
208/120 volt, three-phase, Wye connected system.
A 240 volt, three-phase Delta connected system may be operated as
a corner-grounded system, where one-phase is intentionally grounded,
and the other 2 phases operate at 240 volts-to-ground. This ground
connection is optional, and not a requirement. But, such a connection
1
