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Yesterday afternoon, I had a GFCI switch trip. It would not reset. I figured I had a ground fault.

I left the home for a few hours and after I returned I was able to successfully reset the GFCI.

The only other factors worth noting are that before I left the house: a) it was raining outside and b) there was a crew from the city doing some work nearby some electrical power grid infrastructure (transformers, power lines, etc.). I did not see them physically on the poles but they had earth moving equipment. I don't have any idea what kind of work they were doing or if it was related to the electrical system at all.

What could possibly explain this fact pattern? In particular, how could the GFCI not be resetting before I left, then suddenly able to reset after I return? Could the problem have been caused (and fixed) from outside the home? Is this something I should worry about repeating and start looking for ground faults or doing some troubleshooting now?

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    \$\begingroup\$ A GFCI (or RCD in the UK) monitors current downstream looking towards your internal wiring and appliances so maybe the rain was dripping on some exposed wiring and causing a ground fault current that tripped the GCFI. When you came home maybe the wiring had dried out? \$\endgroup\$ – Andy aka Dec 12 '18 at 15:01
  • \$\begingroup\$ @Andyaka: For clarity: Are you saying the problem must exist "downstream" from the GFCI? And by "downstream," meaning between the GFCI and the appliances? Say, the microwave oven? And not upstream, say, between the GFCI and the main fuse box panel in the garage? In other words, I should be looking at the appliances to find the fault and not the rest of the wiring in the house? \$\endgroup\$ – Mowzer Dec 12 '18 at 15:45
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    \$\begingroup\$ Note that any outlets on the exterior of your house must be gfci protected and could be on a circuit that also serve inside outlets. Basement outlets could also me susceptible to moisture. In addition, water from roof leaks sometimes flows inside walls without being noticed. \$\endgroup\$ – Charles Cowie Dec 12 '18 at 15:48
  • \$\begingroup\$ @Mowzer that is what I'm saying. But it could be wiring, an outlet getting wet or a faulty appliance. \$\endgroup\$ – Andy aka Dec 12 '18 at 15:50
  • \$\begingroup\$ @Andyaka: In that case, then unplugging all the appliances should allow me to reset the GFCI, correct? \$\endgroup\$ – Mowzer Dec 12 '18 at 15:53
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A GCFI (or RTD) works along these principles: -

enter image description here

It monitors hot (live) and neutral wires and if it sees a current flowing down one wire that isn't flowing in the other wire (called a differential current) then the current transformer produces a voltage that is used to activate a trip relay (sensor relay). Notice the test button is used to create such an effect by forcing a small current through only the neutral wire.

If water (for instance) is dripping onto an AC outlet (imagine that is the yellow hand in the picture) then current flows through live (hot) directly to ground and does not flow back through neutral hence the current transformer is imbalanced and produces a signal that trips the relay and power is disconnected.

If the fault occurs inside an appliance then try removing the appliances and restarting the GCFI but only remove the appliances with power off else you run the risk of electrocution.

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