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GFCI Question


Mark P
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There is a GFCI breaker in the panel for the kitchen outlets. When the test button, on the breaker, was pushed the breaker trips as it is designed; however when I used a tester at the kitchen outlet the breaker did not trip off. The tester shows two yellow lights until I push the button and then it changes to red/yellow (reversed polarity). I'm thinking something is wired wrong. What does the brain trust think?

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Testers always do that when "trying" to cause a ground fault so I don't think it means you have a problem. All of the GFI outlet (and likely breaker) manufacturers specify the only true way to test is with the 'test' button on their equipment. As long as that works it's fine.

I would never have found what you describe since I stopped carrying the 3 prong tester with a GFI test button for this exact reason.... and I got sick of moving mountains of stored items to reset the GFI I tripped.

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House built in 1947. Updated panel maybe 10 years old. I did not pull the outlets to rule out false grounds, but that is a good point. It there were a bootleg ground then the tester would not work in tripping the GFCI breaker.

The more I think about it - I like the false ground idea. Makes sense for now. I'll sleep on it and decide how to write it up in the morning.

Thanks Terry

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It would still trip with the tester with a bootleg ground. Did you test your tester on any other GFCI recepts? They have a habit of dying. Did you happen to check whether power to the kitchen receptacles was actually cut off when you tripped the breaker (maybe mislabeled?)

Yes the tester worked on other GFCI outlets.

Yes, I confirmed power was off at the outlet when the breaker was tripped.

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It would still trip with the tester with a bootleg ground.

You sure about that Richard?

A home that old was originally built with a 2-wire system. I know that the typical three light tester will not trip a 2-wire GFCI outlet however the outlet will trip by using its internal test button. If it has a bootleg ground it is still a 2-wire system (neutral hooked over to the ground).

I've never run into a GFCI breaker or outlet that was on a false ground circuit so I've never had the opportunity to test first hand.

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I've never run into a GFCI breaker or outlet that was on a false ground circuit so I've never had the opportunity to test first hand.

If the tester creates a fault or imbalance by shunting some of the current to a ground then it won't trip the GFCI if there's a false ground. The circuit remains balanced; the diverted current is still following its intended path.

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I've never run into a GFCI breaker or outlet that was on a false ground circuit so I've never had the opportunity to test first hand.

If the tester creates a fault or imbalance by shunting some of the current to a ground then it won't trip the GFCI if there's a false ground. The circuit remains balanced; the diverted current is still following its intended path.

Makes sense. If a GFCI receptacle has a bootleg ground the tester will trip it but if the GFCI is downstream, the tester wont trip at a regular receptacle upstream with bootleg ground (as in Jim's scenario).

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For the record, can someone describe 'bootleg ground' and 'false ground'? The only terms I'm certaqin of are 'grounding connection present' and 'grounding connection not present'.

Marc

This is a bootleg ground, Marc.

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I've never run into a GFCI breaker or outlet that was on a false ground circuit so I've never had the opportunity to test first hand.

If the tester creates a fault or imbalance by shunting some of the current to a ground then it won't trip the GFCI if there's a false ground. The circuit remains balanced; the diverted current is still following its intended path.

Makes sense. If a GFCI receptacle has a bootleg ground the tester will trip it but if the GFCI is downstream, the tester wont trip at a regular receptacle upstream with bootleg ground (as in Jim's scenario).

No the tester shouldn't trip it in either case.

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It will trip if the GFCI has a bootleg ground. Try it yourself.

I did and it does. I took apart a GFCI outlet here at the home, put a bootleg ground in, and it did indeed trip it. Don't have any GFCI breakers so can not test that. The outlet I picked was about 20' away from the main box if that matters.

I'm not sure why it worked though. When you have a jumper from the netural to the ground it is just an extension of the netural. When you press the test button it *should* be just like testing a 2-wire outlet outlet no?

Perhaps Doug or Jim can chime in.

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Terry, as I know you know, the tester shunts a bit of current from the hot to ground, un-equalizing the load and tripping the GFCI. With the downstream GFCI, this wouldn't be "noticed" by the circuit in the downstream GFCI breaker because with the bootleg ground you have the same current through the neutral as before pushing the test button. But, at the actual receptacle you are testing, the GFCI circuit is upstream from the bonded neutral and ground, the circuit "notices" that some current has been shunted away from the neutral.

Like Chad said, there's no imbalance downstream, only at the actual receptacle.

Don't know if I explained that well, I didn't "get" it until I read Chad's post.

I think you could build a device to check for bootleg grounds using your tester and a plug-in GFCI receptacle but it makes my head hurt to figure out how to wire it.

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Keep in mind there are plenty of other ways to "boot leg" a ground aside from the neutral to ground jumper at the outlet. Most of which we would rarely find.

You could bond an outlet to a co-ax cable box and likely get a decent ground reading.... it doesn't mean it's a good or correct ground.

How many times have you been in an old basement or crawl space and seen a 70 year old ground clamp on a water pipe? Again, wrong but will light the three prong tester in question to read "correct".

Personally, I consider the "grounded" readings I get at the outlets compared to the number or ground wires I see at the panel to get a general idea of what's going on. When I get suspicous I'll pull a few outlets to look for the ground to neutral jumper which often pops up when things aren't adding up.

One thing I know for sure.... I'll never find every incorrectly grounded/bonded outlet in an older house and make no claim to.

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