Maintenance Tips & Tricks – 2000 – #6

By Plant Engineering Staff August 1, 2000
Finding faults
Problem: Is there an easy way to locate a ground circuit fault in electrical wiring for a 120-V circuit?

Solution: Install a pig-tail lamp holder with an inserted bulb in series with the faulted wiring to quickly isolate the ground fault.

1. Turn off the circuit breaker and remove the load wire and connect it to one of the pig-tail wires. The second pig-tail wire is connected to the breaker.

2. Turn the breaker back on and the bulb should light, which indicates a suspected ground fault.

3. If possible, start by disconnecting half of the entire circuit at an accessible outlet box. If the light stays on, the fault is in the part of the circuit that is still energized. If the light shuts off, the fault is downstream from the energized portion and should be reconnected to proceed with the test.

4. Continue to disconnect circuit wiring until the ground fault is pinpointed and subsequently isolated for repair.

5. Repair the wiring and reinstall the load wire on the circuit breaker.

This procedure can be undertaken by one electrician, but works best with two equipped with radios. One electrician remains at the breaker panel to watch the test light and turn off the breaker as required, and the other works on the faulted field wiring.

Contributor: Warren Moulaison, Central Campus Maintenance Supervisor, Department of Facilities Management, Dalhousie University, Halifax, Nova Scotia, Canada; 902-494-3891;

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