GFCI Leakage Current

Formula

Description

A Ground Fault Circuit Interrupter (GFCI/RCD) monitors the difference between line and neutral current. When this imbalance exceeds the trip threshold (typically 5 mA for personnel protection or 30 mA in some regions), the device disconnects power within 25-40 milliseconds. The leakage current through a ground fault path follows Ohm's law, depending on the voltage and the impedance of the fault path through the person or equipment to ground. Understanding leakage current helps verify that GFCI protection will activate in a fault scenario.

Variables

• I — Leakage current through the fault path (A)
• V — Voltage between live conductor and ground (V)
• R — Total resistance of the ground fault path (Ω)

Practical Notes

GFCI trip thresholds: UL 943 requires 4-6 mA for Class A devices (US), IEC 61008 specifies 30 mA for Type AC RCDs (EU). Some equipment has inherent leakage current due to EMI filter Y-capacitors (typically 0.5-3 mA), which can cause nuisance tripping. For sensitive environments like bathrooms and kitchens, use 5 mA GFCI devices. Medical equipment may require even lower thresholds.