Home>Discussions>ELECTRICAL & LIGHTING>What would cause a GFCI to trip the circuit breaker?
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marklbucla
What would cause a GFCI to trip the circuit breaker?

I just replaced a two prong outlet in the bathroom with a new Leviton GFCI. When I turned the power on, the outlet was not on. I pushed the reset button and then I saw a bit of a flash from the outlet and the circuit breaker tripped.

I have very old wiring- the kind that is fabric insulated. The box tested that it was grounded with my little voltage indicator with the little light on it, but I didn't connect a ground wire yet. All I did was connect the hot wire to the brass side of the line and the neutral wire to the silver line side. Nothing else was done.

I then put the old two prong outlet back on and it appears to be working as normal again.

What could have caused this pop and flash from the GFCI outlet when I pushed the reset button for the first time? Did I install it incorrectly or is there something else going on?

Re: What would cause a GFCI to trip the circuit breaker?
marklbucla wrote:

I just replaced a two prong outlet in the bathroom with a new Leviton GFCI. When I turned the power on, the outlet was not on. I pushed the reset button and then I saw a bit of a flash from the outlet and the circuit breaker tripped.

I have very old wiring- the kind that is fabric insulated. The box tested that it was grounded with my little voltage indicator with the little light on it, but I didn't connect a ground wire yet. All I did was connect the hot wire to the brass side of the line and the neutral wire to the silver line side. Nothing else was done.

I then put the old two prong outlet back on and it appears to be working as normal again.

What could have caused this pop and flash from the GFCI outlet when I pushed the reset button for the first time? Did I install it incorrectly or is there something else going on?

Since the three lamp tester indicate a grounded receptacle without the ground wire being connected you either have BX, AC or MC cable going to a metal box which is actually providing a weak ground to the receptacle...
or you have the white wire touching the side of a metal box. This is called a "bootleg ground" and is not safe.

The three lamp testers can't show two correct lamps unless a ground is connected. And, the ones with a GFCI test button won't trip a GFCI device either.

Since the breaker didn't trip until you pushed the reset button you can assume the wiring is OK, unless the GFCI receptacle was loose and moved the frayed wiring against the ground wire or metal box.

Then the only thing left would be a bad GFCI receptacle. But if it test OK then it's supposed to be OK.

Just to be safe, I would return it to the store for credit. And, look over the wiring in the box for black pits where the wire may have arched over. Rather than get a replacement GFCI receptacle, install a GFCI breaker which will both protect the cable to the receptacle and any loads plugged into it.

I've never heard of a bad GFCI receptacle causing your problem, but it's quite common to have an overtightened (usually because they were tightened with a cordless screwdriver) romex, BX,AC or MC cable connector cause this problem.

If the GFCI breaker won't stay set, you have faulty wire, which must be replaced.

marklbucla
Re: What would cause a GFCI to trip the circuit breaker?

The tester I used at the time was the one with two needles and the little light in the middle to verify that the 2 prong outlet had a ground on it.

After returning it to the original 2 prong outlet configuration, the three light tester showed an open ground with a cheater plug that wasn't screwed into the faceplate. With it screwed in to the faceplate, the three light tester showed that it was wired correctly.

Re: What would cause a GFCI to trip the circuit breaker?
marklbucla wrote:

The tester I used at the time was the one with two needles and the little light in the middle to verify that the 2 prong outlet had a ground on it.

After returning it to the original 2 prong outlet configuration, the three light tester showed an open ground with a cheater plug that wasn't screwed into the faceplate. With it screwed in to the faceplate, the three light tester showed that it was wired correctly.

That confirms what I stated in post #2.

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