Problem with GFCIs and the ground (both 120V and 12V)

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Jack2

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Jun 7, 2021
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Cheyenne, WY
Guys,

I just routinely checked my GFCI outlets. None of them trips. They used to work OK couple of months ago. I could understand one of them died, but none of them actually trips when tested! The tester shows "OK" (ground, neutral, and hot are wired proprely) after I plug it but when I keep "GFCI test" button pressed on a tester, it changes the status to "no ground", but GFCI does not trip.

The other thing I noticed (I didn't try that before) is that 12V ground and 120V ground are connected. Is that expected? If not, could this cause the problem?

Thanks,
J.
 

Lou Schneider

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GFCI test buttons shunt a small amount of the incoming AC current to ground. This unbalances the incoming (hot) and outgoing (neutral) lines and trips the GFCI. It sounds like you have a high resistance connection in the ground line somewhere between the GFCI outlet and the actual ground inside the power pedestal. It's enough to keep the ground voltage low enough to satisfy the little 3 light tester but gets pulled upwards when the GFCI shunts it's little bit of current to it.

It's normal for the negative 12 VDC to be tied to the same point as the AC ground. What you want to avoid is having the AC ground and neutral connected together in an RV. These are normally tied together in a house because it only has one electrical panel so it's a main panel. An RV is a subpanel in the park's electrical system. You keep ground and neutral separate in a subpanel, the only place they're connected together is at a main panel.
 

Bob K4TAX

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My GFI test device is a standard 3-pin plug / cap, with a 7-watt 120-volt incandescent lamp in a socket. One wire is connected to the HOT terminal and the other wire to the GROUND terminal. Nothing is connected to the Neutral terminal on the plug. Plug it in, the GFI should immediately trip.

With an ohm meter, you can measure the resistance between the Neutral and Ground contacts of the receptacle. It should show an open circuit. Thus Ground and Neutral are NOT connected to each other. I suggest doing this with the RV power cord NOT PLUGGED IN. Just in case you goof and hit the hot leg. It saves the meter.
 

Pedro Dog

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An RV is a subpanel in the park's electrical system. You keep ground and neutral separate in a subpanel, the only place they're connected together is at a main panel.

This is 100% correct, but even though technically ground and neutral are not bonded in the RV, the cable from the RV to the pedestal connects them as they are bonded at the main panel. So if you take an ohmmeter inside the rv and measure between the neutral and ground it will read a short as long as you are connected to the pedestal.

If you unplug from shore power, the short will be an open.

Also, if you use a generator, unless you ground it or use a cheater plug, neutral and ground will be separated in the RV.
 
Last edited:

John From Detroit

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Davison Michigan
Guys,

I just routinely checked my GFCI outlets. None of them trips. They used to work OK couple of months ago. I could understand one of them died, but none of them actually trips when tested! The tester shows "OK" (ground, neutral, and hot are wired proprely) after I plug it but when I keep "GFCI test" button pressed on a tester, it changes the status to "no ground", but GFCI does not trip.

The other thing I noticed (I didn't try that before) is that 12V ground and 120V ground are connected. Is that expected? If not, could this cause the problem?

Thanks,
J.
Re 12 volt and 120 volt both grounds being the same.. Absolutely normal. Ground is after all. Ground There is only one Ground (Chassis ground) in an RV..

As for the GFCI not tripping.. Try the test button on the GFCI itself. also try a different TLT-Tester it might be the tester that's failed.
 

Ray-IN

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IMO the home-made "tester" has a problem. Every GFCI receptacle has a "test" button on the face. What happens when you push that test button?
When a GFCI receptacle is first in a 120VAC circuit, it protects every receptacle downstream too.
 

Kirk

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As for the GFCI not tripping.. Try the test button on the GFCI itself. also try a different TLT-Tester it might be the tester that's failed.
That is exactly what I would do first.
is the trailer safe or not?
A non-working GFCI does not mean that the RV is unsafe to use but it does mean that if you plug something defective into one of your outlets the GFCI will not protect you from getting electric shock or worse. I would troubleshoot the problems but would not be afraid to use the RV. Just don't put off resolving the problem.
 

Jack2

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Cheyenne, WY
With an ohm meter, you can measure the resistance between the Neutral and Ground contacts of the receptacle. It should show an open circuit. Thus Ground and Neutral are NOT connected to each other. I suggest doing this with the RV power cord NOT PLUGGED IN. Just in case you goof and hit the hot leg. It saves the meter.
Thanks Bob TAX. Just checked the resistance. There is no connection between neutral and the ground.
Later today, I will try replacing the cable connecting trailer with the power box.
The GFCI tester is good. I tested it in a building.

J.
 

Jack2

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Cheyenne, WY
IMO the home-made "tester" has a problem. Every GFCI receptacle has a "test" button on the face. What happens when you push that test button?
The GFCI outlet trips as it supposed to. BTW, the tester is fine, I checked it in a building.

Thanks,
J.
 

Jack2

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Jun 7, 2021
Posts
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Cheyenne, WY
Problem solved! The ground prong in a cable powering the trailer was loose. When unpluged it and plugged again, the prong fell-off.

Thank you all for your support! Otherwise, I'd be looking elsewhere!

J!
 

John From Detroit

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Just FYI, Jack- K4TAX is a ham radio call sign, and has nothing to do with taxes. The "4" designates the call area that includes Tennessee.
Just like on some forums I'm John WA8YXM (Also a ham call. Though the format is Technician class (Currently the lowest class) I'm an Extra.
Or as I once responded to a comedy meme of a woman telling her daughter Ham Radio operators make the best husbands.
"Of course we do. we have Extra Class, it says so right on my license".

Over the last couple years of COVID Ham radio has been a real sanity saver.
I can talk to people all over from a nice socially safe distance of anything from a couple blocks to several thousand miles.
 

Pedro Dog

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That true only if it is an external (portable) generator. The generator physically installed in most motorhomes and some trailers will be have neutral & ground bonded.

Thanks Gary, I overlooked that some trailers have generators and my answer reflected my experience with my trailers.

So in essence with a built in generator, when on shore power the pedestal is the main panel and the RV distribution panel the sub. But when switched over to onboard generator, it becomes the main panel but without an actual earth ground. So maybe it would be a good practice to connect the RV to earth (ground rod) for extra safety?
 
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Gary RV_Wizard

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So maybe it would be a good practice to connect the RV to earth (ground rod) for extra safety?
Since the generator is the source of the power, bonding neutral & ground at that point is all that is needed. The generator itself is grounded to the RV chassis.

The same applies to an inverter when in use. It becomes the system power source and provides neutral & ground bonding, plus the inverter itself is grounded to the chassis.
 

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