A ground-fault circuit-interrupter (GFCI) is an electrical device, either a receptacle or circuit breaker, which is designed to protect people from electric shock. GFCI protection should not be confused with ground-fault protection for equipment or grounding in general. Even if a system is properly grounded, minor faults in a circuit can cause a dangerous shock to a person using an appliance or power tool. A GFCI de-energizes the circuit when the leakage current level reaches 5 ± 1 mA in 1/40th of a second. This value of current is well below heart fibrillation levels. Ground-fault protection of equipment (GFPE) is defined in the National Electrical Code (NEC) [1] in Article 100 as “a system intended to provide protection of equipment from damaging line-to-ground-fault currents by operating to cause a disconnecting means to open all ungrounded conductors of the faulted circuit. This protection is provided at current levels less than those required to protect conductors from damage through the operation of a supply circuit overcurrent protection device.” A GFPE can be set up to 1,200 amperes with a time delay up to 1 second for ground-fault currents of 3,000 amperes or greater, which would be lethal to a human being.
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