backfeed?


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Old 07-03-14, 06:47 AM
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backfeed?

I'm have a house built in the late 50s a 12-3 with ground has been used for two separate circuits sharing the ground and neutral. One circuit has a GFI the other is a garbage disposal.

My problem is, when I connect the garbage disposal it trips the GFI when I turn it on. It also trips the GFI when I use my voltage tester between the hot line and the neutral, but is OK testing hot to ground 110 volts.
The GFI circuit tests as correct wiring.

Note; I have found in the house where two circuits have been connected to the same outlet tripping both breakers, that has since been fixed, it also does not involve the circuits I'm having a problem with.
I only mention this because this house clearly has wiring problems.
Thank you.
 
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Old 07-03-14, 07:17 AM
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Did you just install the GFCI device? Is this a newer circuit that was installed or is it original to when the house was built?
 
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Old 07-03-14, 12:13 PM
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the wiring is original to the house, I added the GFI. I added two light fixtures bypassing the GFI breaker. one can light, one low voltage under cabinet light. Both are unaffected when the GFI trips.
It's possible the circuit had this problem to start with, but adding the GFI has made it more of a issue, what do you think?

One more thing, I can get the disposal to work by using the ground as a neutral on the G/D. Unfortunately I did not check the wiring when disconnecting the G/D to see if it was wired using the ground as neutral.
 
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Old 07-03-14, 12:24 PM
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Welcome to the forums.

It also trips the GFI when I use my voltage tester between the hot line and the neutral, but is OK testing hot to ground 110 volts .
Ok.... right there.... that is incorrect.

Your GFI should trip when testing from hot to ground.... not hot to neutral. You have something incorrectly wired with the ground and the neutral. It sounds like they are reversed.
 
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Old 07-03-14, 03:15 PM
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Not sure how I could have mixed the two, it's not possible I would have seen that, but I'm wondering if maybe they are touching each other in some way that I'm not seeing, I'll check again. They are medal boxes, I don't care much for.
 
 

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