There are two types of grounding: equipment grounding for safety of people, and system grounding for protection of equipment. Both of these have features in common, and both are important for the proper operation of an electrical system. We begin with equipment grounding because of its vital importance, and its influence on system grounding. We discuss system grounding in a subsequent section.
The fine-print note following NEC Article 250-1 defines these two aspects of grounding:
"Systems and circuit conductors are grounded to limit voltages due to lightning, line surges, or unintentional contact with higher voltage lines, and to stabilize the voltage to ground during normal operation. Systems and circuit conductors are solidly grounded to facilitate overcurrent device operation in the case of ground faults."
"Conductive materials enclosing electrical conductors or equipment, or forming part of such equipment are grounded to limit the voltage to ground on these materials and to facilitate overcurrent device operation in case of ground faults."
