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Thread: Bad breaker or ground fault?

  1. #16
    Retired Defense Industry Engineer jadnashua's Avatar
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    Sometimes, the only rational way to isolate the problem is to start disconnecting things until the remaining circuit works properly. Once you've isolate a branch, continue with disconnecting things or bypassing individual items until you're only left with one. While a GFCI device can fail, if it turns on and trips when you hit the test button, while not an absolutely 100% check, it's close...swapping it with a new one where the same thing happens is pretty much 100%. Then, it's back to trying to isolate the problem. First thing is to carefully open and do a very thorough visual inspection of everything that's accessible. Understanding how the things works helps. You'd never want the neutral and ground tied together after the panel.
    Jim DeBruycker
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  2. #17
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by cacher_chick View Post
    JW, I appreciate your input, but still, I am waiting to hear what methods you might use to track down the problem.
    Quote Originally Posted by jwelectric View Post
    Trouble shooting anything such as this can be a brain teaser and very hard to find even for the most experienced of electricians.
    There is no easy way

  3. #18
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by cacher_chick View Post
    JW, I appreciate your input, but still, I am waiting to hear what methods you might use to track down the problem.

    Don, the scope could certainly show some anomalies that a simple meter would not. As interesting as it might be, I try to stay away from the rocket science. I don't think many residential electricians are running around with a scope.

    This was a problem that I resolved some time ago. I am still fishing for better ways to diagnose such faults. It's pretty easy to locate the source of this kind of problem when the circuits are exposed. It becomes much more challenging for me when I am looking at a finished room and don't know how the circuit is wired.

    In retrospect, I am not so much looking for theory or possibilities. I am interested in hearing what regular electricians do when they walk into a job like this. What testing tools do you grab and where do you start?

    I am surprised that no one suggested using a megger to test the wiring. In outdoor equipment, ground faults are very often caused by moisture and poor or damaged insulation. Maybe this is not a common tool for most electricians?

    Most real electricians should have a o-scope and a megometer available to them. A VOM does not tell all.

    Handheld scopes are cheap and used for working on 3 phase systems and looking at line noise. Meggers are great for testing wire runs and true ground faults. You can also use a Ground Fault tester.

    Many "residential electricians" are wire runners and do not have the proper tools for testing, but they can follow color codes and wiring drawings. No need to even read or speak English.
    Theory only works perfect in a vacuum.

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  4. #19
    Moderator & Master Plumber hj's Avatar
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    quote; The neutral is not shared.

    Are you absolutely certain that there is NO OTHER circuit using the neutral wire? Does the neutral go DIRECTLY to the panel box so you can be sure of it.
    Licensed residential and commercial plumber

  5. #20
    Jack of all trades DonL's Avatar
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    It sounds like there was a Neutral connected to a Ground somewhere, or a wire was damaged like JW mentioned. Or the GFCI was bad.

    A ground to Neutral connection would show a problem if a Load was enough to drop the voltage and the GFCI could detect it.

    With no or little load the GFCI can not see the difference because the Ground and Neutral are bonded at the panel, and the potentials are the same with no load or voltage drop on the wire run.


    I think the problem is known and has been fixed, this was just a test.


    P.S. The neutral may have been shared, with a ground.
    Last edited by DonL; 03-22-2013 at 11:08 AM.
    Theory only works perfect in a vacuum.

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  6. #21
    DIY Senior Member bluebinky's Avatar
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    Quote Originally Posted by hj View Post
    quote; The neutral is not shared.

    Are you absolutely certain that there is NO OTHER circuit using the neutral wire? Does the neutral go DIRECTLY to the panel box so you can be sure of it.
    Unhook the neutral and hot (load side) from the GFCI breaker and measure the resistance (VOM and/or megger) between the neutral wire and the neutral bar -- it should be open.

    In my limited experience with residential wiring (I am not a pro in that area), it's not uncommon for neutrals from different circuits to be intentionally tied together (obvious DIY hacks), but in that case, a GFCI breaker *should* always trip with a load on either circuit, and in theory possibly even without any load at all -- depending on the design of breaker.

    I still think what you describe sounds like a flaky breaker. Probably a manufacturing defect...

  7. #22
    Test, Don't Guess! cacher_chick's Avatar
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    As I mentioned before, this was an issue that I resolved some time ago. The reason for my post was to gain insight on how others would go about diagnosing such a problem.

    It was a neutral to ground short, and while my ohmeter showed infinity, the megger did not.

    I started at the panel and spit the circuit in half twice before being confident that it was in the lights. Unfortunately, I had to cut apart all 4 recessed cans to pinpoint the fault. The lights were split wired with 12-3 from 2 switches, and the short was located where the last recessed can junction box NM cable clamp was tightened on the cable.

    After replacing the lights, I loaded the circuit over 20 amps and the GFCI breaker never as much as whimpered.
    Last edited by cacher_chick; 03-22-2013 at 06:35 PM.

  8. #23
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by cacher_chick View Post
    The reason for my post was to gain insight on how others would go about diagnosing such a problem.

    the megger did not.
    You answered your own question. This type problem is never easy to find

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