Mysterious breaker trip

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Beach004

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I just had my kitchen totally remodelled--all new lights and outlets were part of it. As I was moving back in, on one circuit I turned on both a microwave and a toaster oven. The circuit breaker blew--no huge surprise. But this morning, I tried to run only the microwave--and the breaker again kicked out. I reset it--no power, until I noticed that the GFIC breaker on that circuit had also tripped. I reset it, and all seems well, so far. But I'm at a loss as to why that breaker in the panel tripped, with only the microwave on it; I've used the microwave probably 50 times before this incident, and three or four today after it; no problem. Anyone have an idea? It's still under warranty--in fact the contractor is coming back this week to install some dimmers; but I'd like to tell him something helpful.
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Beach004
 

Jadnashua

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I'd probably try to put the microwave and toaster oven on separate circuits so you won't overload things. But, the tripping of the GFCI is a bit more troubling, as that doesn't trip on excess current, but on unbalanced power (i.e., some of it leaking and not following the return path). That COULD be an appliance issue, but it could also be a wiring problem where maybe there's a nail, staple, kink where the wire is caught between something and not enough to trip the breaker, but will trip the GFCI. It only takes an unbalance of about 5ma, where the breaker needs more than 20A, that's 2,000x more power to trip.

FWIW, I had a troubling circuit that would trip the GFCI intermittently with NOTHING plugged into the circuit. I eventually tracked it down to one segment of the daisy chain, and replaced that wire...it's been fine for years since. Never did figure out what caused it, just ran a new wire...probably a nail or something, and depending on the humidity levels, or the whims of the gods, caused it to trip. It could also be a defective GFCI, but that's much rarer (I'd tried replacing that first to no avail). At the beginning, this might have only happened once every couple of months, but over several years, it started to occur more often until eventually, it would not stay on (i.e., wouldn't let me reset the GFCI) at all, which is when I finally got around to fixing it. It was easier to run a totally new wire from the panel than stringing a new one between the two receptacles and I abandoned the defective one in place.

This is a case where a megger might verify whether the wiring was suspect. Those are similar to a DMM on ohms, but they apply a high voltage on the wire and look for leakage to verify the insulation is intact. They aren't inexpensive, and an electrician may not own one, but it is a good diagnostic tool for checking wiring for faults...if it were a direct short, it would always trip the breaker, and that's not the case here, so it takes a bit more specialized tool and the knowledge of how to use it.
 

Beach004

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I'd probably try to put the microwave and toaster oven on separate circuits so you won't overload things. But, the tripping of the GFCI is a bit more troubling, as that doesn't trip on excess current, but on unbalanced power (i.e., some of it leaking and not following the return path). That COULD be an appliance issue, but it could also be a wiring problem where maybe there's a nail, staple, kink where the wire is caught between something and not enough to trip the breaker, but will trip the GFCI. It only takes an unbalance of about 5ma, where the breaker needs more than 20A, that's 2,000x more power to trip. QUOTE]

Thanks! I will ask the contractor to look into this. I'm most puzzled, though, by the panel breaker tripping this morning, with only the microwave; that just makes no sense to me--but then, neither does 'lectricity...
 

Reach4

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Does the breaker in the panel have a little test button?
 

Beach004

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No, the panel breaker, as far as I can tell, is identical to the ones above and below it, and is probably the same breaker that has been in the box for 20 years, just now connected to different outlets.
 

Reach4

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OK. So the fact that that the older breaker popped means this was not a minor current leak or arcing event. I would inspect under the covers of each outlet that this GFCI handles, and look for shorts. I would wiggle things and try to induce a short. A GFCI can protect outlets other than the outlets that are part of the GFCI if wired for such.

You can leave the covers on, and probably that is the better idea, and still try wiggling the plugs plugged into that outlet and nearby outlets. If a wiggle trips something, that will be informative to your electrician. You already have helpful information for your electrician with what you have already observed.

The microwave oven is not eliminated as the possible cause so far.
 

Jadnashua

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Two more things come to mind...it's possible the CB is toast. They usually can handle problems without destroying itself, but may not always. The breaker might be an arc fault breaker, and it might be tripping because it is sensing arcs, often from a loose connection. Those might also cause the GFCI to trip.
 

WorthFlorida

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I've one time had a breaker trip with any kind of load on it. A replacement fix it. But before you change things eliminate and isolate this problem. You have a CB and a GFCI tripping. GFCI can go bad and I've had a few burn out at my place of work where a contractor use some heavy electrical tools on the circuit.

But first thing I would do is get an extension cord and plug the microwave into it and plug the extension cord in another circuit in the home without a GFCI. Run the microwave, if all is good, turn on the toaster oven in its original circuit. if all is good, plug in a lamp into the outlet where the microwave was plugged into and turn on the lamp. if the GFCI trips, replace it and try it again, if it still trips then there is a bad connection or short downstream from the GFCI. Also try the microwave on another circuit with a GFCI such as the garage or bathroom. If things start tripping it's the microwave.

I hope I made it clear, just eliminate the appliances and still see if the problem occurs. If the problem goes with the appliance then it is the appliance. But there could be a short from the remolding such as was said, a nail or screw pierced a wire.
 
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