Bathroom outlets tripping garage GFCI

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TubeGuru

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My retired neighbour asked me if I could take a look at the GFCI outlet in his garage, which he said would no longer reset. I probably didn't need to, but I replaced the 35 year old outlet with a new one, and when I turned the breaker back on, the GFCI tripped. In these older homes, the breaker panel feeds the garage GFCI outlet, and there are two downstream loads - another outlet in the garage, and the outlets in each of three bathrooms. I disconnected the load going to the bathrooms and the GFCI stays set, and both the GFCI and other garage outlet are working.

As for the three bathroom outlets (two upstairs, one downstairs), there is nothing plugged in. So here's my question: what kinds of faults are common in this situation, and what is the best way to figure out the problem? I'll obviously have to pull the bathroom outlets out of the boxes and look for obvious things like moisture or arcing, and I suppose I could just replace all of the outlets. Would resistance measurements between the hot, neutral and ground help zero in on the defect?

Thanks!
Walt
 

Reach4

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Unplug everything in the bathrooms. Isolate the wires going from the garage to the bathrooms. Measure resistance of isolated wires to ground. That should give an idea of the nature of the fault.

You could put each bathroom on its own GFCI.
 

jadnashua

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What he has would not meet today's electrical code, but that's for another day! You may end up needing to resolve it by running new wires.

I had a similar situation, and isolated it to one electrical wire run...nothing plugged in, tripped the GFCI. Since I had something with a larger load I wanted to install, I ran a new wire to that location, and removed the daisy chain feeding it, and that circuit has been fine since.

My guess, if there's nothing obvious (there wasn't in my situation), is that there may be a nail, staple, screw through the wire and after the years, it's causing some issues...could be rust particles that weren't there when new or maybe the house shifted a little, or lots of other things.

If there's room in the electrical panel, I'd consider running a new lead and power the bathrooms separately from the garage. Per today's code, they should have dedicated 20A, GFCI protected circuits (it should not go out of the bathroom, and only power the bathroom). I do not know if that circuit can be shared in bathrooms (at some point, it could, but I think that is no longer true - you'd need to verify that to be safe).

I'd try to isolate which bathroom(s) are causing the problem, and that will dictate which one needs the new power feed.

If you're really lucky, you'll find something that's causing it, but it may not solve anything by replacing the receptacles or switches. You need to look at all of the light fixtures and fan(s) as well, but being on switches, shouldn't be an issue until you flip the switch, but the switch itself could be a problem. Keep in mind that the power could feed through the fan or light fixture on its way to the switch, so you need to look in those boxes as well.

All it takes is 5ma of leakage current from the hot side to ground...the power going in must equal the power coming out to complete the circuit, otherwise, the GFCI detects the imbalance, and trips. IOW, everything that leaves on the hot needs to return on the neutral, or there's a problem.
 

WorthFlorida

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Do not over look the exterior outlets. My home built in 1990 is the same. One GFCI in the garage feeds three bathrooms and three outside outlets. It's all daisy chained and next to impossible to new run direct wires with a two story on a concrete slab.
 

jadnashua

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The way to try to isolate where the issue is, is to start opening up electrical boxes and disconnecting the feed-through segment. See what no longer has power, and if the GFCI can be reset. It may be tedious, but you should be able to tell how the cables are run.
 
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