EARTH ELECTRODE SUBSYSTEM
Earth grounding is defined as the process by which an electrical connection is made to the earth. The earth
electrode subsystem is that network of interconnected rods, wires, pipes, or other configuration of metals which
establishes electrical contact between the elements of the facility and the earth, This system should achieve
the following objectives:
a . Provide a path to earth for the discharge of lightning strokes in a manner that protects the
structure, its occupants, and the equipment inside.
b . Restrict the step-and-touch potential gradient in areas accessible to persons to a level below the
hazardous threshold even under lightning discharge or power fault conditions.
c . Assist in the control of noise in signal and control circuits by minimizing voltage differentials
between the signal reference subsystems of separate facilities.
2.1.1 Lightning Discharge. A lightning flash is characterized by one or more strokes with typical peak current
amplitudes of 20 kA or higher. In the immediate vicinity of the point of entrance of the stroke current into the
earth, hazardous voltage gradients can exist along the earth's surface. Ample evidence (2-1)* exists to show
that such gradients are more than adequate to cause death. It is thus of great importance that the earth
electrode subsystem be configured in a manner that minimizes these gradients. The lower the resistance of the
earth connection, the lower the peak voltage and consequently the less severe the surface gradients. Even with
low resistance earth electrode systems, the current paths should be distributed in a way that minimizes the
gradients over the area where personnel might be present.
*Referenced documents are listed in the last section of each chapter.