GFCI question

[danwelch]

Our Dometic refrigerator is popping GFCI breakers when it runs on 120 volts. I pulled the heating element and it has three leads, one of which is the ground. Connecting these directly to a GFCI circuit at home, the GFCI pops after about a minute – just like at the campground. If I reset the GFCI, it will pop again immediately - until the element cools down. This is very reproducible behavior. So I am replacing the heating element – but I am very puzzled!

My mediocre electrical knowledge would suggest that the energized element is shorting to ground (the element casing) once it heats up and expands. However – here is the odd part – my Fluke electric meter says otherwise. The element has two white leads and these ohm out at 102 ohms. Spec says 104 ohms - excellent. The meter shows NO continuity (infinite resistance) between the white leads and the ground wire - even after the element is heated up and the GFCI is popping. The ground wire and the outer casing of the element are connected – near zero resistance. (That is appropriate.) So, what gives? Why is the GFCI popping?? Any ideas are welcome!!

[aruba5er]

WAY too much thought about gfci and shocks. I firmly believe in them, but the other day I installed a gfci outlet in a bathroom and could Not make it trip using my wiggy tester to the hot water, coldwater or water spout nor to the drain and pop up. I ran a wire to the heat register and could not get a ground. (the ducting was not connected thru the floor) only after I ran a cord (3 wire) from another outlet could I get a ground that would trip the new outlet/curcuit. With all the plastic plumbing today, the shock threat is way down. Not to be confused with an rv and someone standing on the ground and touching frame or alum skin.

[danwelch]

Yeah people rail at them because they trip easily in wet conditions. But you are right - they are just doing their job. If they are leaking current because are wet, then a regular outlet is a fire hazard and an electrocution hazard. I'd rather have them trip...

[brulaz]

allenm wrote:

...
Personally, I think it's a lousy idea for refrig or freezers. I don't think I've ever had a GFCI outlet at home that didn't eventually go bad. I've also had new ones trip with high humidity.

On my RV the AC outlet is just inside the vent door. Seems like a GFCI outlet would be subject to tripping during rain or high humidity in that case. Of course, they could use a GFCI circuit breaker, which is more expensive.
...

Off topic, I know, as it sounds like the OPs problem is the element not the GFCI socket.

But not sure if it's a bad idea to have the frig on a GFCI outlet.

Rather it's a bad idea to allow that outlet to be somewhere that easily gets wet?

I was careless when washing my old trailer and the frig's GFCI socket took a day to dry out, during which we were running on propane.

And with the current trailer, the outside GFCI sockets will trip after a day's driving in the rain. Again, after a day or so of drying out, they are fine.

Guess there's a reason why GFCIs are used in possibly wet places.

[Rvpapa]

An ohmmeter cannot measure an air-gap using low voltage batteries, but 120 AC will have no problem. If you want to meter it get a megger.
Art.

[danwelch]

I have a Dometic 2193. It is actually a two lead element with the third wire being a ground. Just to be clear - I have been testing connectivity between either of the two element leads and the ground lead. And I get nothing, even when it is heated up and popping GFCI breakers. When it does pop a breaker I quickly test the connectivity and then reset the breaker - but it won't stay on until after it cools 5-10 minutes. I would think that when it is warmed up and in its behavior pattern of popping the breaker, that I would sense at least SOME connectivity between the element leads and ground. But that is not what I see. Anyway, new element is on order...

[Chris_Bryant]

Out of curiosity- do you have the RM8555 ? That's the only Dometic I am familiar with that has a 3 wire element.
You could. I suppose, hook it to a non-gfi outlet, stick a milliamp meter in the ground line and see what happens, though that doesn't really pinpoint the fault. I was going to say you could stick it in the ground wire for the element, but the element is also grounded through the cooling unit.

[DrewE]

danwelch wrote:

I suppose it could be a very minimal ground fault. I know the GFCI breaker is supposed to trip at 5 mA, but using ohms law, (Volts = Amps x ohms) at 110V and .005A a resistance of 22,000 ohms could trip it. I don't know what the specs on my Fluke meter is but perhaps at 22,000 ohms it reads "infinite"? That is the only explanation that makes any sense to me. In any case, I'll have it replaced when the part arrives and we'll see what happens.

Your fluke can easily (and accurately) measure 22 kOhms. This is not a particularly high resistance value for electronics. The top range on my Fluke can measure 22 MOhms, or a thousand times that resistance. I suspect you can't detect it because the fault is not a purely ohmic fault—that is, the current it conducts is not a linear function of voltage. Not everything follows Ohm's law.

[Gjac]

I went through this same thing several years ago. I hate to just replace parts without knowing why the part is bad. Mine ohmed out correctly also but still tripped the GFI. Others on this forum said just replace it and the new element worked fine.

[danwelch]

To answer the questions about the GFCI outlet/breaker - three different GFCI protected devices have tripped. One in the 110 outlet at the campground. I disconnected from that and went to the 30A campground outlet (with no GFCI protection)and the GFCI in my RV tripped. The refrigerator is plugged into that circuit. Finally, when I brought it home, I plugged it into a GFCI protected outlet and the home outlet is tripping. Clearly it is not a problem with the GFCI outlet/breaker.

I suppose it could be a very minimal ground fault. I know the GFCI breaker is supposed to trip at 5 mA, but using ohms law, (Volts = Amps x ohms) at 110V and .005A a resistance of 22,000 ohms could trip it. I don't know what the specs on my Fluke meter is but perhaps at 22,000 ohms it reads "infinite"? That is the only explanation that makes any sense to me. In any case, I'll have it replaced when the part arrives and we'll see what happens.

Thanks all!
Dan

[grizzzman]

allenm wrote:
I've heard some places now require refrigerators to be on GFCI outlets in new home construction. Hadn't realized some RV manufacturers were going that way too. My 2016 Starcraft (division of Jayco) still has a regular outlet for the refrig.

Personally, I think it's a lousy idea for refrig or freezers. I don't think I've ever had a GFCI outlet at home that didn't eventually go bad. I've also had new ones trip with high humidity.

On my RV the AC outlet is just inside the vent door. Seems like a GFCI outlet would be subject to tripping during rain or high humidity in that case. Of course, they could use a GFCI circuit breaker, which is more expensive.

My ranting aside... I think I would try to isolate your problem. Maybe disconnect just the heating element and leave the rest of the refrig electronics connected? I imagine you've tried plugging other things into the outlet to see if it ever trips? Or replaced it?

I was testing my outlets for a inverter installation on my 2016 Rockwood (Forest River) and found that all the outlets are GFCI protected and the the circuit breaker is for the frig. The GFCI is also by the entrance door. Perhaps your frig is on a GFCI circuit?

[allenm]

I've heard some places now require refrigerators to be on GFCI outlets in new home construction. Hadn't realized some RV manufacturers were going that way too. My 2016 Starcraft (division of Jayco) still has a regular outlet for the refrig.

Personally, I think it's a lousy idea for refrig or freezers. I don't think I've ever had a GFCI outlet at home that didn't eventually go bad. I've also had new ones trip with high humidity.

On my RV the AC outlet is just inside the vent door. Seems like a GFCI outlet would be subject to tripping during rain or high humidity in that case. Of course, they could use a GFCI circuit breaker, which is more expensive.

My ranting aside... I think I would try to isolate your problem. Maybe disconnect just the heating element and leave the rest of the refrig electronics connected? I imagine you've tried plugging other things into the outlet to see if it ever trips? Or replaced it?

[BB_TX]

A GFCI will trip if it detects as little as 5 milliamperes difference between the current flow thru the hot pin and the flow thru the neutral pin in the outlet. That small current can leak thru a high resistance ground fault.

Could also be a GFCI going bad.

[DrewE]

Possibly the leakage is happening through some material that isn't exactly an ohmic connection, but rather breaks down under comparatively high voltage—such as a minute air gap. It might be interesting in a scientific investigation sort of way to see if the voltage at the ground lead with respect to either input changes as the element heats up (obviously with the ground disconnected).

I guess it's somewhat of a moot point, really, since the element is plainly defective and needs replacement, regardless of what you can measure with your Fluke. It doesn't take much current leakage to trip a GFCI.