This morning we woke up to the bathroom lights not working. Investigation reveals that the culprit is the GFCI that serves two bathrooms and the laundry room.
It still pops in 10-15 seconds with no draw whatsoever on anything that appears to be connected to the circuit. (I haven't gone through the house looking for stray outlets on the line, though.)
My first thought was a bad GFCI but a couple of other things come to mind also:
1) Two days ago we replaced every bulb on the circuit with LED lights.
2) It's pouring rain, something that happens a few times a year here. We certainly aren't aware of any water leaks but I could imagine water coming down a vent pipe and then going somewhere.
Do I just replace the GFCI and hope it works? Is there some means by which I can test if there is an electric problem? (With the GFCI popped wouldn't it show infinite resistance between the hot and the neutral and between the hot and the ground?)
Edit: Replaced the GFCI, I get exactly the same behavior. I've loosened every bulb on the circuit, no change. Notably I'm getting very low (the highest I observed was 2v) but non-zero voltages downstream of the GFCI when the wires are hanging loose. That's with a decent multimeter so it's possible this is just induced current from somewhere.
Edit again: It apparently is water related somehow. In the days after the rain it was slower and slower to trip, now it's behaving correctly. I can't see how water could get anywhere near the wires, though, let alone to any junctions. If it happens again I can try disconnecting things to find the culprit.
Best Answer
You say that after the rain and some period of drying the GFCI returned to normal working condition. Indicates your problem is "outside" related or influenced. Take a real good look around the outside of your building. Look for any plugs that may be catching moisture from above as the rain comes angling in.
Often as an electrician I come across previous wiring in homes where they jumped the inside GFCI to outside plugs to save money on spec homes. Home owners complain that outside plugs are not working yet breakers are un-tripped. I always say go look for a GFCI in one of the bathrooms, if it is tripped then reset it.
So if you have a non-contact tester you could turn off the breaker that supplies the inside GFCI, and test to see if any plugs on the outside of house are off. If so, make sure that any waterproof covers are in good state and replace them if they appear to be in poor state. If you have a cord plugged in for any length of time you should have a "in-use cover" installed.
Even a small amount of moisture leaking over the receptacle will cause small current leaks to neutral and therefore trip the GFCI and you will not be able to reset it till it is dry. Also any foreign materials will exacerbate the situation. So surfaces should be dry and clean on the receptacle.