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-V systems, particularly 277- or 347-V lighting branch circuits. Ground-fault circuit interrupters (GFCIs) have saved many lives on 120- and 120-240-V single-phase systems since being introduced to the National Electrical Code (NEC) in 1971. Application of GFCIs at voltages higher than 120 V 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 “nuisance trips.” This paper first describes the mechanism of electrical shock, let-go threshold current, and heart ventricular fibrillation. It then describes the three-phase GFCI 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 V phase-to-phase.