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My RV is running 120v off an inverter, if that matters.

One circuit is for everything in the rear of the RV and goes from the breaker panel to a GFCI in the bedroom and then branches out to all 4 receptacles in the bedroom - it also feeds the receptacle in the bathroom too.

Replaced the old GFCI in the bedroom and made sure to get the live wires from the panel into the LINE side and the other two sets of wires on the LOAD side. It lights up green. So far so good.

Then tried replacing the GFCI in the bathroom. It will not reset. Pressing the RESET button just gets me a red LED on the receptacle.

Took that same GFCI into my house and tried it on a regular circuit and it does reset properly and gives a green LED, so it is not defective.

So why doesn't it work in the bathroom in the RV?

A) There could be a short between the first GFCI and the bathroom box, but then wouldn't the first GFCI trip?

B) Do I actually need a GFCI in the bathroom if its already protected by one in the circuit? I'm guessing it's code because every bathroom seems to have one.

C) How do I find out what's making it fail to reset?

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    If you trip the GFCI in the bedroom, does the one in the bathroom lose power? On the GFCI in the bathroom, is anything attached to any of the LOAD terminals? Anything at all? – Harper Aug 2 '18 at 23:19
  • Hmm, no it doesn't. Still has power. The GFCI in the bathroom does have another set of wires leading to another plug but I haven't even reattached those while I'm doing this troubleshooting. – McDazed Aug 3 '18 at 1:20
  • Just discovered a possible clue. I plugged in the RV so it would switch over to 120v shore power. The GFCI in the bathroom now resets and shows green. I unplugged the shore power and let the inverter take over which happens in a split second. The GFCI still showed green. But when I hit the Test button now it would not Reset and just showed red... so maybe its just that my inverter is not grounded? Although I'm not sure why the bedroom GFCI would work on inverter power but not the bathroom? – McDazed Aug 3 '18 at 1:47
  • So it sounds like the bathroom GFCI is actually on another circuit, or at least is not downstream of the bedroom GFCI. You can test that definitively by tripping one and seeing if the other loses power, and vice versa. I wonder if this is a neutral-ground issue with the inverter and/or transfer switch. Does the transfer switch throw neutral? Is your house side power a 3-prong NEMA 10 type connector (like old dryers use)? It does not have ground. – Harper Aug 3 '18 at 4:09
  • A bathroom GFCI should not be fed from the load side of the bedroom GFCI, you don't want the two in series. – fixer1234 Aug 3 '18 at 7:16
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I've recently started working on a similar issue with an inverter from one of our work trucks. The built in GFCI failed, so I replaced it, but no luck.
It turns out that Modified sine wave devices often cause problems for GFCIs because, apparently, of the harmonics that exist when it is not a proper sine wave.
I found, after much deep googling, a couple older articles from Xantrex, the manufacterer of my particular inverter.
This article is from 1997. It states that you should not test a GFCI when it is active and not under load as it will definitely trigger the GFCI. However, all GFCIs since 2015 are required to be selftest.
This article is from 2005 and talks about how even with non-self-testing GFCIs, some will work with some inverters and not others because of the peculiarities of the individual circuits. It contains a chart where they have done some testing with their array of products against a variety of GFCIs. Unfortunately, that was 13 years ago and of course, none of those part numbers are available any longer. Again, all manufacterers were required to make all GFCIs self testing by UL 943 effective June 29th, 2015.
I have been attempting to make contact with an RV technician to find out the scoop on what they are doing currently, but so far have had no luck.
For your situation, I feel that this explains why the one GFCI works when you feed line power or when you installed it in the house. I'm not sure why you're not having a problem with the other one. Are they the same model? Perhaps it's just luck of the draw manufacturing variances.

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