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Understanding the difference between GFCI and GFPE is essential for anyone involved in electrical inspections, installations, or enforcement. While both detect ground faults, they serve entirely different functions. GFCI is for personal protection. GFPE is for equipment protection. They are not interchangeable, and misapplying one for the other is a common and dangerous mistake.
A Ground-Fault Circuit Interrupter (GFCI) is designed to protect people from electric shock. It constantly monitors the current flowing through the hot and neutral conductors and trips when even a slight imbalance is detected, usually due to current leaking to ground through a person. Class A GFCIs trip at ground-fault currents of 6 milliamps or more and will not trip below 4 milliamps. And they react fast, typically in 25 milliseconds or less. That speed is critical because a ground fault of even 100 milliamps can cause ventricular fibrillation if it lasts more than a fraction of a second. GFCIs are required in bathrooms, kitchens, garages, outdoors, and other areas where water and electricity could interact, as detailed in NEC 210.8.
Ground-Fault Protection of Equipment (GFPE) serves a different purpose. It's designed to detect and clear line-to-ground faults that, while not high enough to trip an overcurrent device, can still cause fire, arcing, or equipment damage. GFPE devices generally trip between 30 and 1200 milliamps, far above the threshold that would protect a person. Article 230.95 of the NEC mandates GFPE on service equipment rated 1000 amps or more for 480Y/277V solidly grounded wye systems. These systems rely on GFPE to prevent catastrophic damage in the event of a ground fault without compromising continuity during normal operations.
One place where GFPE is absolutely critical—and often misunderstood—is marinas, boatyards, and docking facilities, as covered in NEC Article 555. These environments are high-risk due to the combination of water, metal docks, submerged structures, and the use of shore power. NEC 555.35 specifically requires ground-fault protection for each feeder supplying shore power to docks, and that protection must not exceed 30 milliamps. This threshold is chosen to shut down power before a dangerous voltage can energize conductive paths, including water.
However, NEC 555 doesn’t stop there. In 555.9(C)(2) and 555.10(B), the code allows for 100 milliamps maximum GFPE in specific scenarios involving overcurrent protection devices for distribution panels supplying marina electrical systems. This higher threshold is used upstream to allow for some level of discrimination between protective devices, ensuring that a feeder fault clears before a main trips, avoiding nuisance outages. It's a layered protection strategy: 100 mA at the main, 30 mA at the feeder or shore power pedestal, and possibly 4–6 mA GFCIs at the receptacles.
The key takeaway is this: GFCIs protect people and must trip fast and low. GFPE protects equipment and must balance sensitivity with system stability. In high-risk environments like marinas, both are needed, and the NEC has defined trip levels accordingly: 30 mA for dock power feeders and 100 mA for upstream distribution, with GFCI still required at the receptacle level per 210.8.
As inspectors, plans examiners, and installers, knowing these distinctions isn’t just a code issue; it’s a life safety issue. Boats, water, electricity, and unaware occupants don’t mix. The NEC recognizes that, and so should we. Know the difference, apply the requirements properly, and enforce them with confidence. Lives and property depend on it.
A Ground-Fault Circuit Interrupter (GFCI) is designed to protect people from electric shock. It constantly monitors the current flowing through the hot and neutral conductors and trips when even a slight imbalance is detected, usually due to current leaking to ground through a person. Class A GFCIs trip at ground-fault currents of 6 milliamps or more and will not trip below 4 milliamps. And they react fast, typically in 25 milliseconds or less. That speed is critical because a ground fault of even 100 milliamps can cause ventricular fibrillation if it lasts more than a fraction of a second. GFCIs are required in bathrooms, kitchens, garages, outdoors, and other areas where water and electricity could interact, as detailed in NEC 210.8.
Ground-Fault Protection of Equipment (GFPE) serves a different purpose. It's designed to detect and clear line-to-ground faults that, while not high enough to trip an overcurrent device, can still cause fire, arcing, or equipment damage. GFPE devices generally trip between 30 and 1200 milliamps, far above the threshold that would protect a person. Article 230.95 of the NEC mandates GFPE on service equipment rated 1000 amps or more for 480Y/277V solidly grounded wye systems. These systems rely on GFPE to prevent catastrophic damage in the event of a ground fault without compromising continuity during normal operations.
One place where GFPE is absolutely critical—and often misunderstood—is marinas, boatyards, and docking facilities, as covered in NEC Article 555. These environments are high-risk due to the combination of water, metal docks, submerged structures, and the use of shore power. NEC 555.35 specifically requires ground-fault protection for each feeder supplying shore power to docks, and that protection must not exceed 30 milliamps. This threshold is chosen to shut down power before a dangerous voltage can energize conductive paths, including water.
However, NEC 555 doesn’t stop there. In 555.9(C)(2) and 555.10(B), the code allows for 100 milliamps maximum GFPE in specific scenarios involving overcurrent protection devices for distribution panels supplying marina electrical systems. This higher threshold is used upstream to allow for some level of discrimination between protective devices, ensuring that a feeder fault clears before a main trips, avoiding nuisance outages. It's a layered protection strategy: 100 mA at the main, 30 mA at the feeder or shore power pedestal, and possibly 4–6 mA GFCIs at the receptacles.
The key takeaway is this: GFCIs protect people and must trip fast and low. GFPE protects equipment and must balance sensitivity with system stability. In high-risk environments like marinas, both are needed, and the NEC has defined trip levels accordingly: 30 mA for dock power feeders and 100 mA for upstream distribution, with GFCI still required at the receptacle level per 210.8.
As inspectors, plans examiners, and installers, knowing these distinctions isn’t just a code issue; it’s a life safety issue. Boats, water, electricity, and unaware occupants don’t mix. The NEC recognizes that, and so should we. Know the difference, apply the requirements properly, and enforce them with confidence. Lives and property depend on it.