How to Use the GFCI and GFPE Trip Level Selector (September 2026 basis)
Unlike countries that standardize on a single 30 mA residual current device, the United States sets the trip level by what is being protected. That is the first thing to get right: a device chosen for the wrong purpose either fails to protect people or trips constantly. This tool pairs the required threshold with the standing leakage already on the circuit and says whether one circuit can carry the load.
Class A GFCI protection for personnel, required by NEC 210.8 in bathrooms, kitchens, garages, outdoors and similar locations, trips between 4 and 6 mA under UL 943, with an inverse time characteristic of about 25 ms at 250 mA. Temporary construction power falls under NEC 590.6 and uses the same Class A devices. EV charging cords use a 20 mA CCID20 interrupter per UL 2231. Ground-fault protection of equipment for heating and de-icing cable is set at 30 mA under NEC 426.28 and 427.22, and it protects the cable, not people. Service disconnects of 1,000 A or more at 480Y/277 V fall under NEC 230.95 instead, where the setting is in amps rather than milliamps.
Nuisance tripping is a leakage problem, not a device problem. Keeping standing leakage below half the minimum trip threshold, so under about 2 mA for a Class A GFCI, is the practical rule, and the calculator reports how many branch circuits that takes when the load exceeds it. Switch mode supplies and IT equipment add roughly 0.5 to 1 mA each, so measure the feeder before adding load. Have a licensed electrician or engineer confirm the final protection scheme.
Frequently Asked Questions
No. The trip level depends on what is being protected. Class A GFCI devices for personnel protection trip between 4 and 6 mA under UL 943, equipment protection GFPE on heating and de-icing cable is set at 30 mA, and EV charging cords use a 20 mA CCID20 interrupter.
Measure the residual current on the feeder with a clamp style leakage meter, or add up the published touch current of each appliance. Switch mode power supplies and IT equipment contribute roughly 0.5 to 1 mA each, so a branch circuit full of electronics reaches several milliamps quickly.
Not where personnel protection is required. A 30 mA GFPE device does not satisfy NEC 210.8, which calls for Class A GFCI protection. The correct fix is to split the load across more branch circuits so standing leakage per circuit drops, and the calculator reports how many circuits that takes.