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Old 06-01-2012, 12:43 AM   #1
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Default Weird ground fault on GFI receptacle

I've been dealing with ground faults on GFI's for decades. Always chased them out by simply opening hot side splices and re-connecting until the GFI tripped. Never been any big deal. Then I met AFCI's and discovered that process no longer works. I chase them (faulted AFCI's) out with an analogue ohmmeter. I've got my process down pretty well. Yesterday I had a call on a tripping GFI. It was a brand new one. I did my usual "chase it through the hot side" routine and that process didn't work. When I realized that what I was seeing was the same thing I see with a ground faulting AFCI, I shut the circuit off and chased with an ohmmeter. In minutes I had the problem cable isolated. I have never seen a ground faulted GFI behave like this. Have any of you? What I am wondering is if the industry has changed their monitoring electronics in GFI's to whatever they are using in the combination AFCI's. There were multiple symptoms that mirrored a faulted AFCI including ANY load across the line, such as turning on a light switch, would trip out the GFI, just like a tripping AFCI would do.
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Old 06-01-2012, 12:57 AM   #2
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I may not be reading your description right, but it sounds like your troubleshooting method is counting on finding a line to ground fault...?

Both GFCIs and AFCIs will respond to neutral-ground faults. Is that what you ultimately found?

-John
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Old 06-01-2012, 01:10 AM   #3
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No, in the past simply removing the hot side and then reconnecting hots one at a time to the line would show up the faulted line. The cables that weren't faulted would tie right back up to the GFI and not trip it, revealing the one that WAS faulted. With AFCI's, and now this GFI that process doesn't work. This faulted GFI mirrored a faulted AFCI. It so perfectly mirrored a faulted AFCI it makes me wonder if we are going to start seeing something different in faulted GFI behavior. This one certainly was different than what I have seen in the past.
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Old 06-01-2012, 01:11 AM   #4
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Old 06-01-2012, 01:13 AM   #5
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Originally Posted by GWPrsqr View Post
...With AFCI's, and now this GFI that process doesn't work....
Alright, I guess my questions is: What is the AFCI or GFCI doing that prevents this method of troubleshooting from demonstrating the problem?

I ask, because with a neutral-to-ground fault you would be able to isolate every hot conductor and no matter which one you reconnected (assuming there's a load on each one) the breaker would trip, because the fault is not in the hot conductors. Is that what you're seeing?

-John

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Old 06-01-2012, 06:59 AM   #6
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You're troubleshooting like a maintenance man instead of an electrician.
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Old 06-01-2012, 11:03 AM   #7
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All I know is in the past I have always been able to chase out a ground faulted cable on a GFI through the hot side, I assume because once the faulted cable is isolated the GFI holds. That process has utterly failed me on faulted AFCI's, and so I developed a new way to find them using an ohmmeter. It's all very simple, the hard part was reaching the conclusion that what I had been doing for decades wasn't working any more. Now I see this same failure of a decades old troubleshooting method on a GFI. It's difficult to describe what I see because there's no consistency to it, and that lack of consistent results became my clue that what I was seeing on this GFI circuit is what I have been seeing on AFCI faults. Once I reverted to my ohmmeter the faulted cable revealed itself in short order. I think I'm just going to abandon my old way and use the ohmmeter every time after seeing this GFI circuit behave like an AFCI circuit. It does make me wonder if the industry has found some less expensive way to monitor for ground faults and that method began being used in combo AFCI's and is going to start arriving in GFI's as well.
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Old 06-01-2012, 11:17 AM   #8
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I wouldn't be surprised if they found a way to save a dollar but using similar technology in the 2.
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Old 06-01-2012, 11:47 AM   #9
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Newer GFCIs have grounded neutral detection.
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Old 06-01-2012, 12:18 PM   #10
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Newer GFCIs have grounded neutral detection.
I thought they all did.
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Old 06-01-2012, 01:38 PM   #11
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I thought they all did.
Only indirectly with the older ones...that is they would trip with current flow on a parallel path for the neutral. The newer ones have circuit that will detect a neutral ground fault without load current.
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Old 06-01-2012, 01:38 PM   #12
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If you can't describe what's happening, it makes it kind of hard to tell you what's going on.

My best advice is to stop thinking about it as "GFCI fault" and "AFCI fault" because that's leading you down the wrong path: Both devices detect ground faults with basically the same technology. Any troubleshooting procedure that works on one will work on the other. If it doesn't, then there's something wrong with the troubleshooting procedure.

-John
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