An electrical grounding system for equipment (such as electrical instruments in an intensive-care hospital room) includes two ground conductors, both connected to a common ground and to the equipment to be grounded and forming a loop. In case of a break in one conductor between the equipment and ground, the other conductor maintains the equipment ground. A ground-integrity checking transformer has a secondary winding of few turns interposed as a series element in the grounding loop and injects only a minimal test voltage in the loop. A primary winding of many turns is used for impressing excitation; and the primary winding is in a test circuit that evidences a break in the grounding loop.