TABLE OF CONTENTS Grounding encompasses several different but interrelated aspects of electrical distribution system design and construction, all of which are essential to the safety and proper operation of the system and equipment supplied by it. Among these are equipment grounding, system grounding, static and lightning protection, and connection to earth as a reference (zero) potential.
Equipment grounding is essential to the safety of personnel. Its function is to ensure that all exposed noncurrent-carrying metallic parts of all structures and equipment in or near the electrical distribution system are at the same potential, and that is the zero reference potential of the earth. Grounding is required by both the National Electrical Code (Article 250) and the National Electrical Safety Code.
Equipment grounding also provides a return path for ground fault currents, permitting protective devices to operate effectively. Accidental contact of an energized conductor of the system with an improperly grounded noncurrent-carrying metallic part of the system (such as a motor frame or panelboard enclosure) would raise the potential of the metal object above ground potential. Any person coming in contact with such an object while grounded could be seriously injured or killed. In addition, current flow from the accidental grounding of an energized part of the system could generate sufficient heat (often with arcing) to start a fire.
To prevent the establishment of such an unsafe potential difference requires that (1) the equipment-grounding conductor provide a return path for the ground fault currents of sufficiently low impedance to...
