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A 15 amp breaker has started tripping. It takes it a minute or two to trip after being reset. I swapped out the wires with the 15 amp breaker next to it, and the "new" breaker now trips instead, so I conclude it's not the breaker that's the problem. It supplies a light in an entryway (which is where the breaker box is) and a light outside, a light in a walk-in closet, two lights controlled by one switch in a bathroom (one in the ceiling and one above the mirror over the sink), a ventilating fan in the bathroom and a GFCI outlet in the bathroom. Nothing is plugged in and nothing is turned on, but it trips anyway. As far as diagnostic tools, I have a multi-meter, I have one of those little screwdrivers that light up if you touch the tip to a live wire, and I have an outlet tester (the kind you plug in and lights come on to tell you if the outlet is wired correctly). I also have standard handyman tools. What would be the best way to set about narrowing down where the problem lies? BTW, it's a doublewide and I do not have access above the ceiling unless I create it myself.
Update: There's a junction box in the light fixture in the entryway. I disconnected wires in turn until I identified the section that trips the breaker. I've narrowed it down to the lighting/fan circuit in the bathroom. I can hear sizzling noises coming from the bathroom when I turn on the power, so I'm going to wait until I've got a helper to narrow it down further. I don't want to burn the house down!
Further update: I found it! A mouse had built a nest in the wall cavity, right where the cable goes through the sole plate, and evidently had done some chewing. The cable is burned up where it goes through the plate. If it hadn't made those helpful sizzling noises I don't know how I would have found it.

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1 Answer 1

I would start with the GFCI by shutting off the breaker, opening the receptacle, disconnecting all the wires, separating all the wires, making sure no one would accidentally touch them, then turning the breaker back on. If I got lucky and the breaker didn't trip, I would hook everything there back together except for the GFCI itself and test the breaker again. If the breaker still trips when all the wires in the GFCI receptacle are disconnected, I'd close up that receptacle, and test the other devices similarly until finding the source of the problem. If there are a lot of wires in any receptacle being tested I would use masking tape to label them and draw a diagram showing where each goes. I've learned this the hard way.

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Thanks for the reply, I started writing my update before seeing your response. One thing I forgot to mention in my update is that my outlet tester indicates hot/ground reverse, and the breaker still trips when all the neutrals are disconnected, so I'm guessing a hot is touching a ground somewhere, but it's not tripping the GFCI. The GFCI seems to have its own supply from the light fixture box in the entryway. –  user20029 Mar 1 at 3:15
    
I wouldn't put any faith in a hot/ground reverse indication of an outlet tester. You can look this up yourself and see what others say about it. And, I don't know why the GFCI is not tripping. I still think you need to check each device on the circuit until you find the source of the problem. After doing the GFCI test I mentioned, I would look at the exterior light, then the bathroom devices because water could have created the problem. I would also look for wires entering a metal box that are rubbing against a sharp surface in the box. –  getterdun Mar 4 at 2:51
    
Thank you for your advice. The problem turned out to be a cable supplying power to heat tape for the water lines under the house. I had no idea it was there. Mice had nested inside the wall, and had chewed on the cable, causing a short. I disconnected that cable completely, so the problem is solved. It was "upstream" of the GFCI outlet, so I think the tester showed a wiring issue because there was current on the ground wire from the short, but did not trip the GFCI because the fault wasn't "downstream" of the outlet. The outlet tester now shows correct wiring at the outlet. –  user20029 Mar 4 at 18:07
    
Glad you got it fixed. –  getterdun Mar 7 at 2:02

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