GFCI vs GFP: Understanding the Difference in Ground Fault Protection

GFCI vs GFP: Personnel Protection vs Equipment Protection

1. Introduction & Context

Ground fault protection devices come in two fundamentally different classes, each designed for a distinct purpose. The Canadian Electrical Code and the US National Electrical Code distinguish strictly between Class A GFCIs, which protect people from electric shock, and Ground Fault Protection devices, which protect equipment from damage and prevent fire. Understanding what each device does — and what it does not do — is essential for specifying, installing, and maintaining the correct layer of protection for a given circuit.

A note on terminology: “EPD” is industry shorthand and is not a defined term in either code. The CEC uses Class A GFCI and Class B GFCI for the two GFCI classes, and Ground Fault Protection (GFP) for higher-threshold equipment protection. The NEC uses Class A GFCI and Ground-Fault Protection of Equipment (GFPE), with Special Purpose GFCI (SPGFCI) added recently for higher-voltage circuits. The principles are the same on both sides of the border; the labels differ.

2. The Core Issue: 6 mA vs 30 mA Thresholds

Class A GFCI — Personnel Protection A Class A GFCI is defined in both codes as a device that interrupts the circuit when ground fault current is 6 mA or more, and does not trip at 4 mA or less. It monitors the current leaving the source against the current returning on the neutral and trips on the imbalance. The 6 mA setpoint is chosen to trip below the let-go threshold — the current at which an adult cannot voluntarily release an energized object (typically around 9–10 mA for adult males per IEC 60479, lower for women and children). Above the let-go threshold, muscle paralysis and respiratory arrest become likely; ventricular fibrillation risk rises significantly above approximately 50 mA depending on current path and duration. A Class A GFCI is engineered to clear the fault before exposure reaches dangerous levels.

Ground Fault Protection (GFP / GFPE) — Equipment Protection GFP and GFPE devices typically have trip thresholds of 30 mA, 100 mA, or higher depending on the application. They are designed to protect equipment and prevent fire — for example, heat trace circuits, large feeder disconnects on grounded-wye systems above 150 V to ground, marina shore power, and similar applications. In industrial practice, equipment ground-fault protection is most often implemented as a separate ground-fault relay or sensing module driving a shunt-trip breaker or contactor, rather than as a single drop-in breaker.

In industrial settings, certain loads produce continuous small leakage currents to ground as part of normal operation — long heat trace runs are the classic example, where distributed capacitance and surface leakage along the trace cable add up to several milliamps over a long circuit. A 6 mA Class A GFCI would nuisance-trip constantly on these circuits. A 30 mA GFP allows normal operation while still detecting larger faults that could damage equipment or start a fire.

A 30 mA GFP device will not reliably protect a worker. By the time it trips, the worker is already past the let-go threshold. GFP is an equipment and fire-protection layer, not a personnel-protection layer. A GFP-protected upstream feeder does not provide personnel protection for downstream receptacles, even though it detects ground faults.

3. Actionable Takeaways

• Diagnose the leakage source on a tripping Class A GFCI; do not defeat or remove it. If a temporary power outlet, hand-tool circuit, or wet-location receptacle keeps tripping, the fault is in the cord, tool, or load — find it. The most common field failure is replacing a tripping GFCI receptacle with a standard receptacle, which silently removes the personnel protection layer entirely.
• Verify protection class is preserved on every replacement. Class A GFCI receptacles and Class A GFCI breakers are the personnel-protection devices encountered at outlets and in panels. Equipment-protection ground fault detection at higher thresholds is typically a separate ground-fault relay or sensing module driving a shunt trip. When a tripping Class A GFCI device is replaced, confirm the replacement is also Class A. Do not assume a higher-threshold equipment ground-fault scheme upstream provides personnel protection at the outlet.
• Do not assume an upstream GFP feeder protects downstream personnel. GFP at the feeder level addresses equipment and fire risk on the feeder; receptacles requiring personnel protection still need a Class A GFCI device at or downstream of the protected outlet.
• Match the protection layer to the hazard. Class A GFCI is the personnel-protection layer required where workers can contact energized parts under fault conditions — wet locations, outdoor receptacles, hand-tool circuits, washdown areas. GFP serves a different function and is not interchangeable, even where it provides ground-fault detection.