The Three-Phase Ground-Fault Circuit-Interrupter System - a novel approach to prevent electrocution

There are many electrocutions that occur on three-phase 480 and 600 volt systems, particularly 277 or 347 volt lighting branch circuits. Ground-fault circuit-interrupters (GFCIs) have saved many lives on 120 volt and 120-240 volt single-phase systems since being introduced to the National Electrical Code^reg (NEC) in 1971. Application of GFCIs at voltages higher than 120 volts has not progressed because the higher voltages to ground result in higher capacitive charging current of branch and feeder circuits, which in turn leads to ldquonuisance trips.rdquo This paper first describes the mechanism of electrical shock, let-go threshold current, and heart ventricular fibrillation. It then describes the three-phase ground-fault circuit-interrupter system (GFCIS-3Ph) that overcomes nuisance tripping by a novel approach to sensing and tripping logic. The system is most applicable for lighting branch circuits due to the historical risk of these circuits, but the GFCIS-3Ph is also appropriate to be considered as an option for all three-phase branch or feeder circuits. Application of the GFCIS-3Ph technology has the potential to almost eliminate electrocution for persons who make direct contact between an energized phase conductor and ground on three-phase systems rated below 1000 volts, phase-to-phase.