2

I have a newly built and wired shop with 3 power circuits for outlets. Each circuit (call them A, B, C) is protected with a GFI at the first outlet and all subsequent outlets on that circuit is on the "Load" side of the GFI.

The GFI on circuit A tripped a couple weeks ago. Nothing is plugged into that circuit. I tried to reset it but it won't reset. I disconnected the Load on the GFI and checked the Line power. It is powered, there is no load, but it still would not reset. I replaced the GFI thinking it was bad and a week later the same thing happened to the replacement GFI!

Yesterday, I pushed the test button on the GFI on circuit B. It tripped the GFI but when I went to reset it, it wouldn't reset. So just as in circuit A, I tried disconnecting the loads on the GFI, made sure it had power on the Line input, but it still would not reset!

Since this is going on with no Load on the GFI, and nothing is plugged into any of them, it is not due to an actual ground fault. (I also checked for downstream ground faults with an ohmmeter and found none.) There is something weird with the wiring between the GFI and the panel, I believe, that is possibly frying the GFI's internal electronics. Perhaps the ground and neutral are not properly connected at the main panel?

BTW, all the work was done by an electrician. He was not sure what is going on so I am sleuthing a bit on this also.

Any ideas?

  • Check if the amperage ratings for the breaker & gfi's match up. – NPM Sep 1 '17 at 14:00
  • Low-grade GFCI's? Failure after 10-15 years of service is unfortunately typical. Failure after a few months is junque and should be a warranty replacement, but if it was junque, the replacement might also be, and you might have to buy something better to get non-junque. You might refer the matter to your state attorney general regarding sales of items unsuitable for their purpose to the public in your state, but basically, don't expect much in that road other than leave a terrible review and don't buy more of those. – Ecnerwal Sep 1 '17 at 14:21
  • @Ecnerwal - I thought it might be a bad batch of GFI so bought a different brand and installed it. I tested it after installing and it seemed OK. A few hours later it tripped itself. Nothing is plugged in to any outlet downstream from it. Its red light was flashing, which according to manufacturer means replace it. I do not think it is bad GFIs, I think it is bad wiring between GFI and panel but I am not sure what to look for. – ScottW Sep 1 '17 at 21:51
  • @ScottW -- post your update as an answer and I'll give you an upvote. That sort of buggyness is definitely out of spec for a GFCI! – ThreePhaseEel Sep 3 '17 at 22:51
2

I noticed some ants on the wall near the GFI box so I took apart one of the units that had failed (i.e., it would not reset, even with nothing on the Load side of the GFI) and found a fried ant across two terminals on the circuit board. Same with the other GFI unit. So the fix is clear - eradicate the ants and replace the GFI. Interesting that an ant can do that to the GFI. Seems like the manufacturer should seal the electronics. Dust could probably do the same thing.

  • They do a number on hard drives as well. In that case, the seal had been chewed through by the ants (there was a seal, but it was not ant-proof - they were very tiny ants but obviously determined.) – Ecnerwal Sep 4 '17 at 3:16
1

An ohm meter will not show all ground faults. A megger is needed to truly verify the insulation is intact. A ohm meter is a low voltage device where meggers are high voltage. If you are running motor loads on these circuits or if there is an industrial site close by this can be damaging the GFCI'S. As stated above inexpensive gfci's may not last and there are "clones" out there that look good but are not UL listed rare but have found this when replacing some almost " new" for a friend that had purchased from the internet and they failed, he thought he had wired something wrong. Wires megged good looking at the outlet closely it was not listed.

  • I removed the load completely from one of the GFIs that is acting weird so it is completely isolated. I tested it (with its button) and it seemed to be working OK. A few hours later it has tripped! Nothing is plugged into it and there is no load on it, so what caused it to trip? I assume its own internal self test failed (it self tests every 3 secs). There is no machinery being used in the building. – ScottW Sep 2 '17 at 2:08
  • Ask your electrician if this is a multi wire branch circuit. MWBC's and gfci's don't play well together. – Ed Beal Sep 2 '17 at 2:15
  • If I understand MWBC, that is what I have. There are four wires coming from the main panel: Green (ground), White, Red, Black. The red and black each are hot and each has its own bus. Each bus is 120V relative to neutral (white), but each bus is 240 relative to each other. So this is 120/240 single phase. What is the problem to be aware of with GFCI and MWBC? – ScottW Sep 2 '17 at 2:33
  • I should add that it surprised me that the neutral (white) and ground (green) were not connected to each other in my subpanel. But I read somewhere they are not supposed to be. – ScottW Sep 2 '17 at 2:37
  • In a sub panel the ground should be isolated from the neutral so that is correct. The problem I have seen with MWBC and gfci's the neutral current from 1 leg can cause nuance trips on the other leg, this is why I mentioned checking with your electrician some times the only place to verify is the panel and the first junction box where they split. I used to pull MWBC'S regulary in years past not so much now with or the last few code cycles because of problems. – Ed Beal Sep 2 '17 at 19:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.