GFCI and Neutral to Ground detection

July 28, 2008, 07:49:10 pm

The recent posts concerning the use of cheater adapters to try to get 50amp sevice from 30 & 15 amp circuits brings to mind an interesting find I had a few weeks ago. My 2000 Allure had a Heart Freedom 20 go bad and it was beyond economical repair. I also noticed that whenever I plugged in the coach to a power source with a GFCI, I always tripped it. So I figured the the inverter was a possible culprit. Since I operate ham radio equipment in my coach, I decided to replace the modified sine wave unit with a true sine wave inverter/charger. I selected the Magnum MS2812.

After I installed the new inverter/charger I still had the GFCI problem. Even when all the circuit breakers were turned off, GFCI trips. The suspected problem was a neutral to ground connection somewhere in the coach.

Since I was doing all these repairs at home, I used a non-GFCI 20amp recepticle to do some tests to determine where the problem was. I made up a test cable using some 10-2 w/ground marine cable so I could isolated each of the wires to measure current draw with a amp clamp meter. With the main and inverter/charger circuit breakers turned on, I put a 10amp load on the system. 10amps was measured on the hot.
However, when I measured the neutral it only had 6amps and the ground had 4amps. The neutral should have returned all 10amps and zero on the ground. This confirmed my neutral to ground problem.

I began the process to troubleshoot each of the circuits and the components. Each test was with power applied and was done outside the coach and without touching the coach. Before moving to the next circuit, power was removed. I began with testing the transfer switch and then the surge guard. I made up a GFCI patch box to test each step of the process without having to put any load on the system. I lifted each ground and neutral of each circuit one at a time until I stopped tripping the GFCI. The first of course was the newly installed inverter/converter. To my surprise it tested good. After a few more circuits, it turned out to be the water heater circuit.

I reconnected all the removed systems except the water heater. I applied power and a 10amp load with the inverter/charger. No trip on the GFCI and 10amps was measured on the hot and neutral and zero on the ground.

Now is it the water heater or did the cable from the circuit breaker box to the water heater have a damaged area somewhere in the run. I hooked up the neutral and ground in the box for the water heater and then lifted the neutral and ground at the water heater. I did another GFCI and amp clamp test and no neutral to ground problem. Thus, indicating a problem with the water heater. Specifically the element.
I removed the element and it physically looks great. However, when tested with an ohm meter, it is shorted internally between case ground and neutral/hot lead terminals.

Moral of this story...If you trip a GFCI at a power pedistal, make sure that your coach is not at fault. Most GFCI's only need 4 milliamps on the ground side to cause them to trip. Our coaches do not have the neutral and ground connected together in the distribution panel like they are in our homes. Be careful....and be sure!

Jim Hughes

2000 Allure #30511

Re: GFCI and Neutral to Ground detection

Reply #1 – July 28, 2008, 08:22:25 pm

Yahoo Message Number: 40046

Jim:

Thank you for the great report on troubleshooting the GFCI problem.
I did not systematically wring out the problem like you did. I replaced the 50 amp GFI with a non-GFI breaker. LOL Seriously, thanks for sharing your findings.
Tom Dunlap
2000 Affinity

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