Enter your System Voltage, Fault Loop Impedance (Zs), RCD/GFCI Rating, Maximum Trip Time, Normal Load Current, and Background Leakage Current into the RCD/GFCI Trip Calculator to find your Fault Current, Trip Margin, Effective Sensitivity, and whether your setup meets Code Compliance.
Fault Current
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Trip Margin
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Effective Sensitivity
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Code Compliance
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RCD (Residual Current Device) and GFCI (Ground Fault Circuit Interrupter) are essentially the same device with regional naming differences. Both detect current imbalances and trip when fault current exceeds their rating.
Loop impedance is measured using a specialized tester that applies a test current and measures voltage drop. The measurement includes transformer impedance, line conductors, and equipment grounding conductor resistance.
Common causes include high background leakage current from equipment, moisture, damaged insulation, or neutral-to-ground faults downstream of the GFCI. Normal leakage should be well below the device rating.
Loop impedance should be low enough to ensure adequate fault current for protective device operation. Typically less than 1.6Ω for residential 120V circuits and proportionally lower for higher voltages.
Yes, RCDs can be tripped remotely using a test circuit that creates an artificial imbalance between live and neutral conductors, similar to the built-in test button function.
High loop impedance typically results from loose connections, undersized conductors, long circuit runs, or poor grounding connections. These conditions reduce fault current and may prevent proper protective device operation.
Common ratings are 5mA (medical), 10mA (special locations), 30mA (general protection), 100mA (fire protection), and 300mA (industrial applications). Selection depends on application and safety requirements.
Standard RCDs should trip within 300ms at rated current, and within 40ms at 5 times rated current. Faster trip times provide better protection against electric shock and fire hazards.