perplexing GFCI problem

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  #1  
Old 09-18-11, 11:10 AM
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perplexing GFCI problem

I have spent hours trying to troubleshoot this one but the solution escapes me.

I have 2 circuits (on 2 seperate breaker switches), circuit 1 with a GFCI in a bathroom (with conitinuations) and circuit 2 without any GFCI but with shared ground with circuit 1.

I replaced the GFCI and all of the outlets on circuit 1 because the GFCI would not stay on. That circuit works fine now, except I have a hallway light on circuit 2 on a 3-way switch, and any time it is switched on, it trips the GFCI on circuit 1.

An electrician and I thought we found the problem in the circuit 2 hallway light fixture but it turns out the light was fine (works on circuit 1). The GFCI on circuit 1 does not trip with circuit 2 hallway light switched on without the hallway light fixture (capped lines). I measured voltage at the source to the hallway light and got proper readings (hot/ground or hot/neutral = 120 and no other voltages detected in any other combo). I plugged a fan into the hallway light source and it tripped the GFIC also. I have verified correct installation of the GFCI (load and line).

I think I have 2 options now:

a) turn off circuit 2 and check continuity on all outlets and light fixtures
b) replace the GFIC and hope I bought a defective one

Any other ideas? TIA
 

Last edited by pcboss; 09-18-11 at 07:55 PM. Reason: GFCI
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  #2  
Old 09-18-11, 11:15 AM
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Besides sharing the ground, are they sharing the neutral? If they share the neutral, that would cause the GFCI to trip.
 
  #3  
Old 09-18-11, 11:17 AM
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When you said the ground is shared did you mean the white neutral or the bare or green conductor?
 
  #4  
Old 09-18-11, 11:21 AM
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Originally Posted by pcboss View Post
When you said the ground is shared did you mean the white neutral or the bare or green conductor?
the switch box for the circuit 2 hallway light has multiple bare wires bundled in a line. Maybe its a wrong assumption, but that would be the only way I can think of to get from circuit 2 to 1 to trip the GFIC when I switch on the hallway light (but only under load - fan or light)

I can check if neutral is shared by turning off both circuits and checking continuity. I can do that for ground also and see if my assumption is correct.
 
  #5  
Old 09-18-11, 11:51 AM
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Ok, I switched off circuit 1 & 2 breakers, plugged an extension cord into the c1 GFIC outlet to reach c2 hallway source and confirmed BOTH ground and neutral are shared.

So do I start dissassembling circuit 2 outlets and fixtures to check continuity (confirming no hot/neutral/ground shorts or miswirings)?
 
  #6  
Old 09-18-11, 12:11 PM
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11 outlets, the hallway light fixture and 2 ceiling fans are on circuit 2.

Given shared ground and neutral between circuit 1 & circuit 2, I'm still puzzled by the fact that only the hallway light on c2 trips the GFIC on c1, and only under load (light or fan). No other outlet or light appears to do that on c2, so should I keep working on the hallway light 3 way switches?
 
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Old 09-18-11, 12:26 PM
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The neutral needs to be pigtailed where the circuit first splits. The GFI is seeing the neutral current from circuit 2 as an imbalance and tripping.
 
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Old 09-18-11, 12:40 PM
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Originally Posted by pcboss View Post
The neutral needs to be pigtailed where the circuit first splits. The GFI is seeing the neutral current from circuit 2 as an imbalance and tripping.
There is a bundle of neutrals capped in the hallway light switchbox. Is this what you mean by pigtailed? I could check continuity from c1 to c2 on these? I assume I need to disconnect the c1 neutral from c2 neutral?

thanks for your responses, this has been really frustrating.
 
  #9  
Old 09-18-11, 04:03 PM
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another couple of hours checking continuity of neutrals between c1 and c2 and found both the 1/2 bath outlet source neutral (on the GFIC, c1) and the GFIC outlet source neutral in the master bath have good continuity with a c2 neutral outlet. I disconnected both of those neutral wires and they separately have continuity with a c2 neutral outlet.

So my status is with the lamp disconnected from c2, everything works. My wife wants the hall lamp back which when connected & turned on by either of the 3 way switches, trips the GFIC on c1.

I'm running out of ideas on how to tackle this (next step)
 
  #10  
Old 09-18-11, 04:20 PM
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Sorry one more potential clue:

When the hallway light is hooked up and I turn the switch on, the GFIC trips, and the light either just blinks on then off or never comes on.

If the hall light is really on c2 then it should stay on after the GFIC trips (on c1)? I'll have to look at that tomorrow.
 
  #11  
Old 09-18-11, 06:38 PM
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circuit 1 with a GFIC in a bathroom (with conitinuations)
It sounds as if your continuations, as you call them, are all GFCI protected. If that is correct, one way to solve your problem would be to leave the GFCI receptacle as a stand alone GFCI and wire the "continuations" to the line side of the GFCI receptacle and not to the load side. It appears all of your testing has finally shown that the hallway light is indeed on a different circuit than you thought (circuit 1 rather than circuit 2). Or, you may have the 2 circuits connected somewhere.
 
  #12  
Old 11-04-11, 05:55 AM
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Originally Posted by CasualJoe View Post
It sounds as if your continuations, as you call them, are all GFCI protected. If that is correct, one way to solve your problem would be to leave the GFCI receptacle as a stand alone GFCI and wire the "continuations" to the line side of the GFCI receptacle and not to the load side. It appears all of your testing has finally shown that the hallway light is indeed on a different circuit than you thought (circuit 1 rather than circuit 2). Or, you may have the 2 circuits connected somewhere.
So that's what the issue was - although there were several continuations in that socket, not all were originally hooked up to the load side of the GFIC because they spanned 2 circuit breakers and there were shared neutrals that automatically tripped the GFIC.

I did as you said - wired it as a stand alone GFIC.

Thanks
 
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