GROUND

1. An electrical connection to earth through an earth-electrode subsystem. ( 188 ) 2. In an electrical circuit , a common return path that usually (a) is connected to an earth-electrode subsystem and (b) is extended throughout a facility via a facility ground system consisting of the signal reference subsystem , the fault protection subsystem , and the lightning protection subsystem . 3. In an electrical circuit, a common return path that (a) may not necessarily be connected to earth and (b) is the zero voltage reference level for the equipment or system.