A bare ground touching a neutral screw kept tripping a new home's breaker: how to find ground-neutral faults

The owner posted the find on Sunday after the breaker had kept tripping for about two years. The National Electrical Code lets the neutral and the equipment ground meet only at the service disconnect. Downstream of it, sections 250.24(A)(5) and 250.142(B) require the neutral to stay insulated from grounding conductors, as Michael Johnston explained in IAEI Magazine. A bare ground resting on a white terminal breaks that rule inside a single box.

The breaker type explains the trips. A GFCI compares the current leaving on the hot with the current returning on the neutral, and a Class A device opens once the two differ by 4 to 6 milliamps, according to a Q&A by Mike Holt. A neutral that touches ground hands part of the return current to the ground wire, and the breaker reads that as leakage. Breakers listed to UL 943 also put a small voltage on the neutral through a transformer, so they can trip on a grounded neutral with nothing plugged in. Combination AFCI breakers with ground-fault sensing may hold until a load comes on, which Holt says leads to a familiar callback: the electrician leaves with the power on, and two hours later the owner calls about dead outlets.

Electricians on Mike Holt's forum, discussing GFCI breakers that tripped overnight with nothing plugged in, offered two ways to hunt for it. One is visual: look for a damaged ground wire rubbing a neutral screw, or a neutral with scraped insulation pressed against the box or the ground screw. A licensed electrician in that thread wrote that the break may be as fine as a hairline and only open up once the wires are folded back into the box. The other is isolation: disconnect the devices on the circuit and cap the wires, then lift the hot and, if trips continue, the neutral at the breaker, until the fault is narrowed to one section.

Holt's Q&A also notes that an overheated neutral terminal can melt insulation and create the same neutral-to-ground contact, inside or outside the receptacle.