About the Book
This book is designed for the contractor who finds that installing grounding systems, which are in compliance with all relevant codes and standards, is a complex and somewhat mystifying assignment. While in larger facilities, the design of a proper grounding system is certainly complex and should be left to a qualified engineer, the everyday grounding installations and applications covered in this text are well within the scope of the qualified contractor. In most facilities, a thoughtful contractor can follow the guidelines and techniques in this book and be reasonably ensured that he has done a competent and code compliant job. This book is not written for the casual contractor who was in the painting business last week. It is for the electrical contractor who intends to be in business next week, next year, and in the years to come. Design and installation of electrical grounding systems is one of the most important aspects of any electrical distribution system, yet it is all too often misunderstood and subsequently installed improperly. Some detailed knowledge of the facility is needed, and the contractor who intends to do the job correctly must make the investment in time and tools - or hire someone to do these things for him. Guesswork won’t do! The subject is too serious and complex for that kind of approach. We hope you find our recommended approaches helpful and cost-effective.
Article 250 of the National Electrical Code (NEC) contains the general requirements for grounding and bonding of electrical installations in residential, commercial and industrial establishments. Many people often confuse or intermix the terms grounding, earthing and bonding. To use simple terms:
Grounding is connecting to a common point which is connected back to the electrical source. It may or may not be connected to earth. An example where it is not connected to earth is the grounding of the electrical system inside an airplane.
Earthing is a common term used outside the US and is the connection of the equipment and facilities grounds to Mother Earth. This is a must in a lightning protection system since earth is one of the terminals in a lightning stroke.
Bonding is the permanent joining of metallic parts to form an electrically conductive path that will ensure electrical continuity and the capacity to conduct safely any current likely to be imposed. A comprehensive review of grounding and bonding requirements contained in the NEC appears in Chapter 3 of this text.
Importance of Grounding
There are several important reasons why a grounding system should be installed. But the most important reason is to protect people! Secondary reasons include protection of structures and equipment from unintentional contact with energized electrical lines. The grounding system must ensure maximum safety from electrical system faults and lightning.
A good grounding system must receive periodic inspection and maintenance, if needed, to retain its effectiveness. Continued or periodic maintenance is aided through adequate design, choice of materials and proper installation techniques to ensure that the grounding system resists deterioration or inadvertent destruction. Therefore, minimal repair is needed to retain effectiveness throughout the life of the structure.
The grounding system serves three primary functions which are listed below.
- Personnel Safety.
- Personnel safety is provided by low impedance grounding and bonding between metallic equipment, chassis, piping, and other conductive objects so that currents, due to faults or lightning, do not result in voltages sufficient to cause a shock hazard. Proper grounding facilitates the operation of the overcurrent protective device protecting the circuit.
- Equipment and Building Protection.
- Equipment and building protection is provided by low impedance grounding and bonding between electrical services, protective devices, equipment and other conductive objects so that faults or lightning currents do not result in hazardous voltages within the building. Also, the proper operation of overcurrent protective devices is frequently dependent upon low impedance fault current paths.
