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About 2 years ago during a kitchen update, I replaced a GFCI outlet with a new one, 20-amp (both pass through and the GFCI outlet itself). Branching downstream from it are two more outlets, one on the other side of the sink, and one right behind it on the outside of the house. It's an up-to-date "lock" GFCI, is wired correctly and has always tested and functioned correctly. Last week having a new roof put on, the roofers plugged a pretty heavy-duty looking air compressor into the outside outlet. After about an hour, the GFCI tripped. Now, plugging just about anything into the outside outlet is causing it to trip after a few minutes' use, for example yesterday, my shop vac. I have used the shop vac in that outlet many times before with no problem. So, my question is, did the current draw by the air compressor damage the GFCI (it still tests fine). If so, I guess I better replace it.

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What happens if you plug (your shop-vac, say) directly into the GFCI? Just trying to sort issues with the downstream outlet and issues with the GFCI. At a guess, the GFCI is probably the issue, but it's a thing to check on (probably with an extension cord, as you won't want to listen to the shop vac running in the house.) –  Ecnerwal Apr 23 at 18:22
    
Good idea. I'll try that tonight (or Saturday). Thanks. –  Greg Apr 23 at 19:03
    
Is it possible that some moisture (rain, dew, condensation, frost, etc.) has recently entered the GFCI? –  wallyk Apr 23 at 19:15
    
The GFCI itself is in a dry location. –  Greg Apr 23 at 20:52

3 Answers 3

I have noticed that GFCIs seem to be worn out by heavy, prolonged loads. I can't find any authoritative sources for this effect. Probably the GFCI manufacturers know all about it.

The bridge circuit which detects the flow imbalance depends on some precision electronics which are heat sensitive. The heavy current itself does not affect them, but the side effect of that current heating up the components will lead to premature failure.

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My experience is that when GFI receptacles trip due to overloads rather than a ground fault, their lifespan is diminished greatly. I have replaced dozens of them over the last few years. To be honest, I think they are sensitive to overloads and simply are damaged. Easier to replace them then deal with a lot of nuisance tripping.

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As to both comments above, heat stress from overload or even lengthy heavy current draw makes sense to me. I am going to plug the shop vac directly into the GFCI to see what happens, but it seems very likely I will be replacing to avoid the nuisance tripping. –  Greg Apr 23 at 20:54
    
I lived in my former house for 15 years, having had it built custom, and never had to replace anything. The house I just bought, built just 15 years ago, has things breaking that I have never seen before, like: toilets, GFCI outlets, and toggle switches. I guess some people are just easier on their house than others. –  user19121 Apr 30 at 20:11

OK, here are the results of my test. I ran the shop vac for about 15 minutes directly off the GFCI, no problem. Then I went outside and plugged it into the load outlet -- dead. I think it tripped the second I plugged the vac in, even though I didn't hear the vac start at all. The reason I think this is because using an LED nightlight as a tester, I see the LED illuminate for like a microsecond when I plug it into the load outlet. And there's more -- even after the load outlets go dead, the GFCI outlet itself still has power, only the two load outlets are dead. My conclusion is, it has to be replaced.

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If anybody is still checking this thread, I replaced the GFCI. The old one was scorched black on its back where the hot line entered, and also on the end of the hot line copper itself. I'm curious whether this indicates that the compressor was a severe overload, or that the GFCI was defective, or something else? –  Greg May 5 at 14:16

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