One Circuit Trips Another

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360Youth

Senior Member
Location
Newport, NC
I don't think I have encountered one quite like this, though some similar. We just finished a remodel job that included rewiring some garage, hall, and bedroom lights. A garage entry (not roll up) door was relocated which meant relocating some switches and junctioning a discontinued receptacle. After the lights were reinstalled and new devices put in, whenever the switch for the garage lights were turned on, it tripped the GFI breaker for the garage receptacle. Separate circuit. Checked out my boxes, everything was fine. Checked for backfeed at the breaker. I suspect a neutral issue. The circuits are in different panels so I could not take neutrals loose from panel to see if they are tied together somewhere. I was able to change breaker to a standard and install GFCI at first receptacle in line and the problem went away. Any ideas, or is it simply a breaker issue? Certainly impossible to troubleshoot through my limited desription, I was just wondering if there have been similar situations that would shed some light. Thanks.
 
360 - I would definitely say your neutrals are tied together somewhere. As soon as you turn on the lights, the neutral current from the lights is traveling through the GFCI breaker. Since the current is not the same on the hot and neutral at the GFCI breaker (because the lights are fed from a different breaker) the GFCI trips. Hope this helps.
 

360Youth

Senior Member
Location
Newport, NC
Yeah, I am sure it is. I just don't know where within the layout of the work we did I could have mixed neutrals and not mixed the hots also. And why does the receptacle hold but not the breaker?
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
I don't think I have encountered one quite like this, though some similar. We just finished a remodel job that included rewiring some garage, hall, and bedroom lights. A garage entry (not roll up) door was relocated which meant relocating some switches and junctioning a discontinued receptacle. After the lights were reinstalled and new devices put in, whenever the switch for the garage lights were turned on, it tripped the GFI breaker for the garage receptacle. Separate circuit. Checked out my boxes, everything was fine. Checked for backfeed at the breaker. I suspect a neutral issue. The circuits are in different panels so I could not take neutrals loose from panel to see if they are tied together somewhere. I was able to change breaker to a standard and install GFCI at first receptacle in line and the problem went away. Any ideas, or is it simply a breaker issue? Certainly impossible to troubleshoot through my limited desription, I was just wondering if there have been similar situations that would shed some light. Thanks.

Maybe the neutral for the receptacle is from the correct panel or upstream from where the possible mixed neutrals are. Just taking a stab at it.:)
 

SG-1

Senior Member
Inductive kickback will also trip a GFI. If there are any transformers on the other circuit they could cause a trip. There is an old thread somewhere here about a GFI tripping & a swimming pool.
 

Fulthrotl

~Autocorrect is My Worst Enema.~
Inductive kickback will also trip a GFI. If there are any transformers on the other circuit they could cause a trip. There is an old thread somewhere here about a GFI tripping & a swimming pool.

well, you say moving the gfci to the first box instead of the breaker solves
this problem? sounds like inductance pick up between circuits that are running
parallell for a good long distance, but most likely is somewhere you have a
neutral connected to another path to ground, either thru some connected
equipment, or most likely, the neutral is grounded somewhere in the field..
if ya have a good circuit tracer, lift the neutral and hot at the panel,
and see if you have continuity between them.... if you do put a signal on it,
and follow it thru the wiring till it dies off, that is your cross connect point.
 

SG-1

Senior Member
Have you tried using a clamp-on ampmeter around the neutral on the circuit that is tripping ?

Will the breaker reset while the offending circuit is energized ?

Does the breaker only trip during switching ?

Try to measure the offending circuits current on both the grounded & ungrounded conductors to see if they are equal. Two in-line meters would be best for this measurement because a 6 milli-ampere difference can cause your problem.

Just some thoughts on some tests to try.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
You really need to take care of the shared neutral problem if you do have one. That is the first order of business.

From my own home experience I did have a bath fan that would trip the freezer GFCI receptacle when it was switched of. The fan was on an entirely different circuit. After trying a different brand of GFCI, I took a semieducated guess and put a snubber at the fan. No trips for about a year now.

The Leviton rep told me later that this problem has been addressed, a fix was in the works and it is not limited to Leviton devices.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
You really need to take care of the shared neutral problem if you do have one. That is the first order of business.

From my own home experience I did have a bath fan that would trip the freezer GFCI receptacle when it was switched of. The fan was on an entirely different circuit. After trying a different brand of GFCI, I took a semieducated guess and put a snubber at the fan. No trips for about a year now.

The Leviton rep told me later that this problem has been addressed, a fix was in the works and it is not limited to Leviton devices.

What is a snubber?
 

cadpoint

Senior Member
Location
Durham, NC
Pssst, it'll be the last place you look...

Then have the circuits broken up / off line and use a pair of telephones and ring it...
 
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Electric-Light

Senior Member
You really need to take care of the shared neutral problem if you do have one. That is the first order of business.

From my own home experience I did have a bath fan that would trip the freezer GFCI receptacle when it was switched of. The fan was on an entirely different circuit. After trying a different brand of GFCI, I took a semieducated guess and put a snubber at the fan. No trips for about a year now.

The Leviton rep told me later that this problem has been addressed, a fix was in the works and it is not limited to Leviton devices.


I know that you can setup a working snubber with a capacitor and resistor, but is there one you can buy that is UL listed for such use?
 

DARUSA

Senior Member
Location
New York City
The answer is that you neutral is tied together before the first outlet. The GFCI outlet protect the line after the outlet!!! Trace it before the first outlet were you install the GFCI outlet.
 
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