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Old 02-23-2011, 11:52 PM   #1
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Why would grounding a line trip the breaker?


Here's my problem. I was installing a GCFI and fixing some of the bad wiring in my garage the other day, and realized that half the receptacles were grounded and half weren't. I opened the ungrounded receptacles, and they all had grounding wires attached, so I followed them back to a junction box where the grounding wire for that line was detached. Ah ha- I thought, and reattached it. But then, my GCFI (which is at the beginning of the line) wouldn't reset- until I detached the grounding wire for that line of receptacles again. I have some other problems, which I'm in the process of correcting (like the junction box is overcrowded)- but the only thing that appears to trip the GCFI is attaching the grounding wire- and only for that set of receptacles. All the others are fine- does anyone have an idea why this would happen?

I'm not sure how old the wiring is, but most of the house is ungrounded, so I don't believe this wiring is original (in fact I can almost guarantee it). I installed new receptacles and checked all the connections- but I am perplexed.

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Old 02-23-2011, 11:59 PM   #2
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Why would grounding a line trip the breaker?


first, make sure there is absolutely nothing plugged into any outlet on that circuit. (not just turned off but actually unplug anything). Then, is there anything else at all powered by this circuit? If so, disconnect it from the circuit.

I would also check for any bootleg grounds (that's where somebody bonds the neutral to the ground terminal in order for it to appear there is a proper grounding system in place.)

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Old 02-24-2011, 02:44 AM   #3
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Why would grounding a line trip the breaker?


Well- the circuit in question is wired like this (as far as I can tell): From the new GFCI receptacle it goes through one receptacle then to a junction box. From the junction box, 1 wire goes to one receptacle, 1 wire goes "somewhere" (I need to track this one down still), and one 1 wire goes down a conduit and feeds two receptacles. It's this last one that seems to have the problem- the other two wires are grounded and have no issues. The 2 receptacles fed by the wire that's causing the fault I checked, nothing was plugged in, the wiring was ok, but I replaced the receptacles with new ones for good measure (a previous owner of my house had painted over them- apparently he felt it wasn't necessary to cover fixtures, wall plates, or even screws before painting). No bootleg grounds I can see. Now the cable that feeds these does run behind the furnace before going through the conduit, so I'm not sure if something might be going on behind the furnace- I suppose I could pull it and make sure there are no breaks caused by heat or rodent- But that's the only thing I can think of at this point.
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Old 02-24-2011, 06:31 AM   #4
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Why would grounding a line trip the breaker?


Use a continuity tester to check between the neutral and the equipment grounding conductors downstream of the GFCI. If you have continuity between those two, a ground and neutral are touching or connected together and this will definitely trip a GFCI.
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Old 02-24-2011, 07:20 AM   #5
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Why would grounding a line trip the breaker?


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Old 02-24-2011, 12:22 PM   #6
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Why would grounding a line trip the breaker?


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Originally Posted by brric View Post
Use a continuity tester to check between the neutral and the equipment grounding conductors downstream of the GFCI. If you have continuity between those two, a ground and neutral are touching or connected together and this will definitely trip a GFCI.
Have to disconnect the circuit neutral from the neutral bar in the panel before doing this test. Otherwise it would be normal (mandatory, in fact) to have continuity between neutral and ground.

I suspect this is the problem. Somewhere on the circuit, the neutral and ground are connected and this is tripping the GFCI.
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Old 02-24-2011, 02:00 PM   #7
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Why would grounding a line trip the breaker?


line side neutral/ground are terminated on neu/ground buss in main panel.this would make no difference.neutral/ground short load side of gfci will trip gfci.you are useing a gfci outlet or a gfci breaker?ok you are useing a gfci recp.re-read post 3.yurn off power,disconnect load side hot and neutral from gfci outlet.connect ohmmeter from neutral to ground.if you see continuity,that is the prob.open all boxes that are on that ckt and check for a short.

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Old 02-24-2011, 05:44 PM   #8
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Why would grounding a line trip the breaker?


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Originally Posted by mpoulton View Post
Have to disconnect the circuit neutral from the neutral bar in the panel before doing this test. Otherwise it would be normal (mandatory, in fact) to have continuity between neutral and ground.

I suspect this is the problem. Somewhere on the circuit, the neutral and ground are connected and this is tripping the GFCI.
Not downstream of the GFCI it wouldn't.
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Old 02-26-2011, 11:27 AM   #9
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Why would grounding a line trip the breaker?


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Not downstream of the GFCI it wouldn't.
Depends on whether the GFCI breaks both the hot an neutral connections from line to load, or just the hot. I'm not sure which it does, would have to test one to see.
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Old 02-26-2011, 11:57 AM   #10
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Why would grounding a line trip the breaker?


I think brric means to disconnect the line side of the GFCI before performing the test. This would include any pigtails at the recept.
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Old 02-26-2011, 12:38 PM   #11
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Why would grounding a line trip the breaker?


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Originally Posted by jlmran View Post
I think brric means to disconnect the line side of the GFCI before performing the test. This would include any pigtails at the recept.
Thank you. I wasn't clear enough. That is what I meant.
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Old 02-26-2011, 02:55 PM   #12
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Why would grounding a line trip the breaker?


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Originally Posted by brric
Thank you. I wasn't clear enough. That is what I meant.
It was quite clear because you stated 'downstream' from the GFCI.

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