Electrical Grounding and Bonding, Sixth Edition
By Phil Simmons
Contents:
Foreword . xi
Preface . xiii
Acknowledgments . xvii
Changes to the NEC xix
Introduction to Grounding and Bonding . 1
Objectives 1
The Mystery 2
Definitions . 3
Review of Ohm’s Law and Basic Electrical Theory . 28
Electric Shock Hazards . 32
Review Questions 34
Unit-1
General 38
Objectives 38
Introduction . 39
250.3 Application of Other Articles 39
250.4 General Requirements for Grounding and Bonding . 40
250.6 Objectionable Current . 52
250.8 Connection of Grounding and Bonding Equipment . 56
250.12 Clean Surfaces 59
Review Questions 60
Unit-2
System Grounding 63
Objectives 63
250.20 Alternating-Current Systems to Be Grounded 64
250.21 Alternating-Current Systems of 50 Volts to 1000 Volts
Not Required
to Be Grounded 69
250.22 Circuits Not to Be Grounded 72
250.24 Grounding of Service-Supplied Alternating-Current Systems . 75
250.25 Grounding Systems Permitted to Be Connected on the Supply Side of the Disconnect. 90
250.26 Conductor to Be Grounded—Alternating-Current Systems . 90
250.28 Main Bonding Jumper and System Bonding Jumper . 92
250.30 Grounding Separately Derived Alternating-Current Systems 97
250.32 Buildings or Structures Supplied by a Feeder(s)
or Branch Circuit(s) 117
250.34 Portable, Vehicle-Mounted and Trailer-Mounted
Generators . 127
250.35 Permanently Installed Generators . 131
250.36 High-Impedance Grounded Neutral Systems . 134
Review Questions 138
Unit-3
Grounding Electrode System and Grounding
Electrode Conductor . 142
Objectives 142
250.50 Grounding Electrode System 143
250.52 Grounding Electrodes . 144
250.53 Grounding Electrode System Installation . 150
250.54 Auxiliary Grounding Electrodes . 160
250.58 Common Grounding Electrode . 161
250.60 Use of Strike Termination Devices . 162
250.62 Grounding Electrode Conductor Material 163
250.64 Grounding Electrode Conductor Installation 163
250.66 Size of Alternating-Current Grounding Electrode Conductor 180
250.68 Grounding Electrode Conductor and Bonding
Jumper Connection to Grounding Electrodes . 183
250.70 Methods of Grounding and Bonding Conductor
Connection to Electrodes 187
Review Questions 189
Unit-4
Enclosure, Raceway, and Service Cable Connections 194
Objectives 194
250.80 Service Raceways and Enclosures 195
250.86 Other Conductor Enclosures and Raceways . 196
Review Questions 197
Unit-5
Bonding . 198
Objectives 198
250.90 General 199
250.92 Services . 200
250.94 Bonding for Communication Systems 206
250.96 Bonding Other Enclosures 207
250.97 Bonding for Over 250 Volts 211
250.98 Bonding Loosely Jointed Metal Raceways . 212
250.100 Bonding in Hazardous (Classified) Locations 213
250.102 Grounded Conductors, Bonding Conductors, and Jumpers 213
250.104 Bonding of Piping Systems and Exposed Structural Metal 219
250.106 Lightning Protection Systems . 225
Review Questions 226
Unit-6
Equipment Grounding and Equipment Grounding Conductors 231
Objectives 231
250.109 Metal Enclosures . 232
250.110 Equipment Fastened in Place (Fixed) or Connected
by Permanent Wiring Methods . 232
250.112 Specific Equipment Fastened in Place (Fixed)
or Connected by Permanent Wiring Methods . 233
250.114 Equipment Connected by Cord and Plug 235
250.118 Types of Equipment Grounding Conductors 237
250.119 Identification of Equipment Grounding Conductors 249
250.120 Equipment Grounding Conductor Installation 252
250.121 Restricted Use of Equipment Grounding Conductors 253
250.122 Size of Equipment Grounding Conductors . 255
250.124 Equipment Grounding Conductor Continuity . 267
250.126 Identification of Wiring Device Terminals 268
Review Questions 268
Unit-7
Methods of Equipment Grounding . 273
Objectives 273
250.130 Equipment Grounding Conductor Connections 274
250.134 Equipment Fastened in Place or Connected by
Permanent Wiring Methods (Fixed)—Grounding 278
250.138 Cord and Plug Connected Equipment . 279
250.140 Frames of Ranges and Clothes Dryers 280
250.142 Use of Grounded Circuit Conductor for
Grounding Equipment 282
250.146 Connecting Receptacle Grounding Terminal
to an Equipment Grounding Conductor 283
250.148 Continuity of Equipment Grounding Conductors
and Attachment in Boxes 288
Review Questions 291
Unit-8
Grounding of Specific Equipment Covered in
Chapter 5 of the NEC . 295
Objectives 295
Introduction . 296
Class I, Class II, and Class III Hazardous (Classified) Locations 296
250.100 Bonding in Hazardous (Classified) Locations 296
Article 517, Health Care Facilities 299
517.11 General Installation—Construction Criteria . 299
517.13 Equipment Grounding Conductor for Receptacles
and Fixed Electric Equipment in Patient Care Spaces 300
517.14 Panelboard Bonding 307
517.16 Use of Isolated Ground Receptacles . 308
517.17 Ground-Fault Protection of Equipment 310
Article 547, Agricultural Buildings . 318
547.9 Electrical Supply to Building(s) or Structure(s) from
a Distribution Point . 318
547.10 Equipotential Planes and Bonding of Equipotential Planes 321
Article 550, Mobile Homes, Manufactured Homes,
and Mobile Home Parks . 323
550.32 Service Equipment 323
550.33 Feeder 326
Article 551, Recreational Vehicles and Recreational Vehicle Parks . 327
551.76 Grounding – Recreational Vehicle Site Supply Equipment 328
Article 555 Marinas, Boatyards, Floating Buildings,
and Commercial and Noncommercial Docking Facilities 330
555.1 Scope . 330
555.4 Location of Service Equipment 330
555.10 Signage 331
555.13 Bonding of Non-Current-Carrying Metal Parts. . 331
555.35 Ground-Fault Protection of Equipment (GFPE)
and Ground-Fault Circuit-Interrupter (GFCI) Protection . 332
555.37 Equipment Grounding Conductor . 333
555.53 Ground-Fault Protection . 334
555.54 Grounding . 335
555.55 Insulated Neutral. . 335
555.56 Equipment Grounding. 336
Review Questions 336
Appendix A: Some Fundamentals of Equipment-Grounding
Circuit Design . 342
Appendix B: Investigation and Testing of Footing-Type
Grounding Electrodes for Electrical Installations 351
Appendix C: Understanding Ground Resistance Testing . 361
Appendix D: Report of Research on Conduit Fitting
Ground-Fault Current Withstand Capability 392
Index . 400
Preface:
Electricity follows the basic laws of physics, regardless of whether it is current flow over ungrounded (“hot”) conductors, over grounded conductors (sometimes neutral conductors), or in the grounding system. So, if we can understand basic circuit flow, we can understand the requirements and performance rules for grounding and bonding of electrical systems and equipment. You will find several of the illustrations in this book to be fairly basic and uncomplicated. This complements the overall effort to make the rules for grounding and bonding as easy to understand as possible and to take the concepts of grounding and bonding back to the basics.
I want to mention here and applaud the efforts of Ronald P. O’Riley, who wrote a book titled Electrical Grounding: Bringing Grounding Back to Earth, through the sixth edition. Mr. O’Riley is now deceased. Although this book is not based on or intended to be a continuation of Mr. O’Riley’s efforts, our goals in presenting a book on grounding and bonding of electrical systems are very similar. Quoting from the preface to Mr. O’Riley’s
sixth edition:
“The author’s wish is for this book to be a learning experience for members, and those in training for a career in the electrical industry. It is the author’s hope that simplifying, illustrating, reasoning through, and coordinating the grounding requirements, as contained in Article 250 of the National Electrical Code®, will promote better understanding and use of the Code. This can result in safer, cleaner electrical installations and maintenance. The first rule is to make it safe: the second is to make it work. Both can be done. With this thought in mind, this book is directed at vocational instructors of electricity, electrical engineers, design engineers, construction electricians making installations in the field, maintenance electricians at factories or buildings, electrical inspectors, and many other members of the electrical industry. It is also the author’s hope that the apprentice or person preparing for a career in the electrical industry and studying the
National Electrical Code® will find the detailed explanations and accompanying diagrams in this book to be an interesting learning experience.” Electrical Grounding and Bonding is based on my many years of experience in teaching subjects related to the NEC, field experience in the electrical construction industry, and association with the International Association of Electrical Inspectors (IAEI).
Other than the Introduction, which includes an explanation of many definitions applicable to electrical grounding and bonding along with a brief review of electrical theory, this book is organized by section number of the NEC. For example, if you’re interested in learning about requirements for a grounding electrode system, you can follow the rule from the NEC Section 250.50 to an identical code reference in this book. Other features of the organization of this book are as follows:
- The requirement from the NEC is included. Note that in most cases, the requirement is paraphrased rather than being a direct quote.
- The requirement is discussed and explained.
- An illustration of the requirement is provided.
- Where appropriate, there is an explanation of how to comply with the rules, such as determining the appropriate size system bonding conductor.