$28.95 U.S. Practical Guide To Electrical Grounding

1 PracticalGuide ToElectricalGroundingPracticalGuide ToElectricalGroundingAnPublicationW. Keith SwitzerW. Keith Switzer$ Printing, First Edition, August 1999 First Printing, First Edition, August 1999G157LT99 Grounding Book COVER 9/10/1999 2:40 PM Page 1 Electrical Protection Products34600 Solon RoadSolon, Ohio 44139W. Keith Switzer, Senior Staff EngineerPhone: (440) 248-0100 Fax: (800) 677-8131E-mail: Of Congress CatalogCard Number: 99-72910 Copyright 1999 ERICO, rights reserved. No part of this work covered by thecopyright hereon may be reproduced or used in any form orby any means graphic, electronic, or mechanical,including photocopying, recording, taping, or informationstorage and retrieval systems without written permissionof ERICO, Guide to Electrical GroundingGrounding Book 4/14/99 10/5/99 6:01 PM Page IFC1 (Black plate)PracticalGuide ToElectricalGroundingPracticalGuide ToElectricalGroundingAnPublicationFirst Printing, First Edition, August 1999W.

2 Keith SwitzerW. Keith SwitzerGrounding Book 4/14/99 10/5/99 6:01 PM Page i (Black plate)Table of ContentsChapterDescriptionPage1 Building and Service Entrance Grounding - 1 The Grounding of buildings and facilities where people GroundingGround ResistanceElectrical Service GroundingUfer Grounding2 Building Lightning Protection- A critical extension of Interior Bonding and Grounding - The bonding and47grounding of building steel, Electrical panels and other powersystems Bars & Ground Bus4 Transients & Other High Frequency Bonding and Grounding Requirements65 The bonding and Grounding of electronic of Components Used in Grounding79 Grounding ConductorsConnectorsGrounding Electrodes6 Special Grounding Situations- Areas not covered elsewhere89 AirportsCorrosion and Cathodic ProtectionRadio Antenna GroundingStatic GroundingWire MeshFences and Gates7 Application of Surge Protection Devices 113 Definitions119 References and Bibliography121 Practical Guide to Electrical GroundingiiGrounding Book 4/14/99 10/5/99 6:01 PM Page ii (Black plate)WHY DO WE NEED ANOTHERBOOK ON Grounding ?

3 This book is designed for the contractor who finds thatinstalling Grounding systems, which are in compliance withall relevant codes and standards, is a complex andsomewhat mystifying assignment. While in larger facilities,the design of a proper Grounding system is certainlycomplex and should be left to a qualified engineer, theeveryday Grounding installations and applications coveredin this text are well within the scope of the qualifiedcontractor. In most facilities, a thoughtful contractor canfollow the guidelines and techniques in this book and bereasonably ensured that he has done a competent and codecompliant job. This book is not written for the casualcontractor who was in the painting business last week. It isfor the Electrical contractor who intends to be in businessnext week, next year, and in the years to come.

4 Design andinstallation of Electrical Grounding systems is one of themost important aspects of any Electrical distributionsystem, yet it is all too often misunderstood andsubsequently installed improperly. Some detailedknowledge of the facility is needed, and the contractor whointends to do the job correctly must make the investment intime and tools - or hire someone to do these things for won t do! The subject is too serious andcomplex for that kind of approach. We hope you find ourrecommended approaches helpful and 250 of the National Electrical Code (NEC) containsthe general requirements for Grounding and bonding ofelectrical installations in residential, commercial andindustrial establishments. Many people often confuse orintermix the terms Grounding , earthing and bonding. To usesimple terms: Grounding is connecting to a common point which isconnected back to the Electrical source.

5 It may or may notbe connected to earth. An example where it is not connectedto earth is the Grounding of the Electrical system inside is a common term used outside the US and is theconnection of the equipment and facilities grounds toMother Earth. This is a must in a lightning protection systemsince earth is one of the terminals in a lightning is the permanent joining of metallic parts to forman electrically conductive path that will ensure electricalcontinuity and the capacity to conduct safely any currentlikely to be imposed. A comprehensive review of groundingand bonding requirements contained in the NEC appears inChapter 3 of this is a copyright of GROUND?There are several important reasons why a groundingsystem should be installed. But the most important reasonis to protect people! Secondary reasons include protectionof structures and equipment from unintentional contactwith energized Electrical lines.

6 The Grounding system mustensure maximum safety from Electrical system faultsand good Grounding system must receive periodic inspectionand maintenance, if needed, to retain its or periodic maintenance is aided throughadequate design, choice of materials and proper installationtechniques to ensure that the Grounding system resistsdeterioration or inadvertent destruction. Therefore, minimalrepair is needed to retain effectiveness throughout the life ofthe Grounding system serves three primary functionswhich are listed safety is provided by lowimpedance Grounding and bonding between metallicequipment, chassis, piping, and other conductive objects sothat currents, due to faults or lightning, do not result involtages sufficient to cause a shock hazard. Propergrounding facilitates the operation of the overcurrentprotective device protecting the and Building andbuilding protection is provided by low impedancegrounding and bonding between Electrical services,protective devices, equipment and other conductive objectsso that faults or lightning currents do not result in hazardousvoltages within the building.

7 Also, the proper operation ofovercurrent protective devices is frequently dependent uponlow impedance fault current Noise Grounding aids inelectrical noise reduction and impedance between the signal ground pointsthroughout the building is voltage potentials between interconnectedequipment are the effects of Electrical and magnetic fieldcoupling are function of the Grounding system is to provide areference for circuit conductors to stabilize their voltage toground during normal operation. The earth itself is not Preface iiiGrounding Book 4/14/99 10/5/99 6:01 PM Page iii (Black plate) Practical Guide to Electrical Groundingessential to provide a reference function. Another suitableconductive body may be used function of a Grounding electrode system and a groundterminal is to provide a system of conductors which ensureselectrical contact with the earth.

8 Two Fine Print Notes(FPN) that appear in Section 250-1 of the NEC provide agood summary of the reasons for Grounding systems andcircuit conductors and the conductive materials whichenclose Electrical conductors and OF GROUNDINGAs noted above, Grounding and bonding are not the addition, not all Grounding is the same. Each chapter orsection in this book will describe one or more of the varioustypes of Grounding and bonding that are widely used in theelectrical industry. Topics of primary interest are: Power System Grounding Including The Service Entrance Bonding Grounding Electrical Equipment Lightning Protection Protection Of Electronic Equipment (Shielding Is Not Discussed) Grounding is a very complex subject. The proper instal-lation of Grounding systems requires knowledge of soilcharacteristics, Grounding conductor materials andcompositions and Grounding connections and complete Guide to proper Grounding is often part ofnational and international standards.

9 For example, IEEEStd 80, Guide for Safety in AC Substation Grounding , is acomprehensive and complex standard for only oneparticular Grounding application. This standard is neededfor proper substation design in an electric powertransmission facility or the power feed to a very largefactory. Smaller facilities can use these design guides also,but such an approach may be too costly. This book takes conservative shortcuts that allow the design of thegrounding system to proceed without undue design emphasize that the approaches in this book, in orderto be conservative and correct, may trade a small increasein Grounding components in order to avoid a largeengineering expense. Remember that any Electrical instal-lation is, and properly should be, subject to a review by theauthority having jurisdiction over the Electrical design and installation personnel are encouragedto discuss and review the Electrical installation with theauthority having jurisdiction PRIOR to beginning any workon the of Electrical Grounding systems also should findthis a handy Guide because we have included extensivereferences to the National Electrical Code (NEC)(NFPA70), ANSI and IEEE Standards as well as otherNFPA Standards.

10 It is not the purpose to be a Guide to theNEC but we will not make recommendations that disagreewith it. Keep in mind that Section 90-1 (c) of the NECstates that the Code is not intended to be used as a designspecification. Still, it is difficult to imagine how personneldesign and construct Electrical systems in the USA withoutreferencing the NEC. Also keep in mind that the NECcontains minimum requirements only. In some cases,minimum standards are not sufficient or efficient for thedesign project. For example, existing standards do not coverthe need to maintain the operational reliability of modernelectronic equipment - especially telecommunications andinformation technology (computer-based) systems. We willcover these situations in this book. Where no standardsexist, the ERICO engineering staff can make recommen-dations based on more than 58 years of written primarily for readers in the and Canada,readers from other nations also will find this work usefulbecause it concentrates on cost-effective, proven book is written around standards with referencesto Canadian Standards.