Can't figure out this electrical issue, HELP Please!

[Theboomanchu]

We recently purchased this Cougar 5th wheel and actually went through all the systems while the sellers were camping near our home and hooked up to 50 A service at the campground.  We had an extensive list (pre-delivery list printed from the library on this site) of components to check and everything worked fine. 

The seller said what he does prior to heading out to go camping is to hook up the trailer to his regular 110v service at home, to start the fridge cooling down the day before they leave using the adapters as shown in the attached picture since he doesn't have 50 amp service at home.  We don't as of yet have a 50 amp plug set up at home for the camper so tried to plug it in as he mentioned.  It immediately trips the GFCI circuit.  I have checked to make sure nothing is turned on, including the electrical side of the water heater to no avail. 

It is obviously a ground (fault?) issue of some sort rather than too high of a current draw, but I don't understand these GFCI outlets well enough and/or the relationship between our house electrical and the trailer.  What am I missing here?  Any Ideas? 

 

[Harvard]

In my opinion, a GFCI cannot be expected to not trip when it is exposed to the entire electrical leakage of an RV, especially a 50 Amp one at that.  All the 3 wire AC wiring plus the appliances such as the converter have capacitive coupling that leaks current from Hot to Ground, which is normal.

 

[BobNSam]

So sounds like the answer is to connect to a non-GFCI outlet. This should not pose any safety issues.

 

[John From Detroit]

Ok, Harvard has a point.... With a 30 amp rig, even leakage is balanced, but on a 50 amp. it might not be.

But there is a tribble slaying sequence you might wish to try before you get too frustrated.

Start by turning off ALL circuit breakers.. Then plug in and plug a drop light in the other half of the house/garage duplex outlet... Turn on the light.. With luck, it will work

Now one at a time STARTING WITH THE MAIN  Turn on the breakers.. MAIN .. Light should stay on.  This is good

Now move on down or along the breaker line.. One at a time.. Turn them on.. When the light goes out turn THAT breaker back off.. Reset the GFCI, (turning the light back on) and continut

Write down the label code for each breaker that turns off the light... Then we can help you once we have that list.

Some Converters and some other devices have a tendency to trip a GFCI.

 

[Theboomanchu]

Thanks, I will try that sequence and get back to you with the results as soon as I can.  I appreciate the info!  Unfortunately, I don't have a "non-GFCI" receptacle anywhere near the camper, so cannot easily plug into it that way, without using several extension cords, which would most likely introduce it's own set of issues.

 

[Gary RV_Wizard]

Just leave the big power consumption devices off, e.g. a/c, and electric water heater and you should have no worries with a long extension cord. I've run a 150 ft with no problems as long as the total load is light, maybe 10-12 amps.

 

[Harvard]

I can almost guarantee you the offending device will be the converter and I am equally confident there is nothing wrong with the converter. Converters have RFI capacitors from Hot to Ground to limit electrical noise emissions from the converter. You just have to use a non GFCI outlet.

 

[gatorcq]

You are trying to run a 50 amp unit on a 15 amp outlet? Is this correct?
First, every item that uses  Vac (plug outlet) must be turned onto Propane or turned off. This includes your water heater. No Air conditioning should be on.

Now you can run the refrigerator on the electric Vac.

So, first I would be more specific as to what you are trying to do, what you are connected to

 

[John From Detroit]

I am in agreement with Harvard it is most likely the converter.. But I have heard of other causes, #2 nad 3 on the suspect list are the electric element in the Water heater, and Fridge.. In that order.

Two more I have read of

1: Loose wire (I am fond of saying many RVers have a few screws loose.. The screws holding wires in assorted places inside the RV)  Making contact with another wire.

2: Junction boxes.. FULL OF WATER tossed up by the wheels when driving.

 

[Theboomanchu]

I verified that the rocker switch on the electrical side of the water heater is in fact off as well as fridge, water pump etc.  Nothing is on and it still trips the GFCI the second I plug it in.  I will run an extension cord to a non GFCI receptacle and give that a try.    I'll let you all know the results.  It does make sense with the capacitor that it would trip the GFCI.  Thanks for all the info!

 

[Gary RV_Wizard]

Of course nothing is going to trip on a non-GFCI outlet. That suggestion is just a stop-gap to get you some power to use. It doesn't help diagnose anything.

I have to disagree with Harvard that "nothing is wrong". While converters and electric heat elements are sometimes a source of ground fault problems, they aren't supposed to be. Certainly not by design!. If properly installed/wired, they will not trip a GFCI.  I'll grant, though, that a ground fault from a converter may well not be dangerous to human life. A GFCI will detect even a tiny trickle to ground, but do you want to gamble?

 

[Harvard]

A thought just occurred to me, typically 50 Amp cables have a plug on each end, a male for the pedestal and a female for the RV.

If that is the case we should be able to rule out the cable by unplugging it from the RV and plug the male 15A/50A adapter into the GFCI.

Does that scenario, just the 50A cord + 15A/50A adaptor, trip the GFCI?

 

[Gary RV_Wizard]

A thought just occurred to me, typically 50 Amp cables have a plug on each end, a male for the pedestal and a female for the RV.

Not sure I would say "typical"  -  some do, some do not.

If that is the case we should be able to rule out the cable by unplugging it from the RV and plug the male 15A/50A adapter into the GFCI.

This would diagnose a hot->ground short in the shore cord itself. Would not diagnoses a neutral->ground short, however.  It eliminates one possible cause, at least.

 

[Lou Schneider]

If you have a multimeter, try measuring the resistance between the Neutral pin (the top pin on the 50 amp plug) and the ground pin.  You should have an open circuit (infinite resistance).

If you have low resistance (a few ohms) you may have neutral and ground bonded together in the RV's power panel.  They're supposed to be kept separate because the RV is a subpanel on the campground's electrical system.  But mistakes do happen and RVs have been shipped with the neutral to ground bonding screw in place.

Bonding neutral to ground allows part of the neutral current to return via the ground wire, which makes the GFCI think there's an electrical fault to ground and it trips.

 

[Theboomanchu]

Thanks!  I do have a multimeter and will check that as soon as I get a chance.

 

[Theboomanchu]

I finally had a chance to do some more diagnostics on the GFCI issue.  I had to work the last 2 weekends plus had an injured dog I had to deal with after work last Saturday (Yes, He's OK).

Anyway, I was able to run an electrical cord to a non-GFCI receptacle.  All the low amp stuff works fine, so at least I know the fridge, etc, are OK.

Now I need to at least check for grounds that might be causing the GFCI receptacle to trip.  I checked the (50A) receptacle on the back of the trailer and tested between the different terminals and the terminals to ground.  With the meter set at all settings up to 20,000 Ohms, I got a good solid infinity.  With the meter set at 200 K Ohms, I would get a jumping reading when I first made contact with the probes but would immediately drop to infinity (capacitor on converter?).  I did start getting some readings with the meter set to 2,000 K (or 2 Million) and 20 M Ohms, but I am not sure which terminals are which.  I assume the two terminals with the extra lugs are the hot legs and the one without the lug is the neutral.  It is obvious that the side terminal plate is the ground.  I don't recall which terminals did have readings nor the values thereof, but if someone could verify my assessment of the terminals is correct, a will get readings. 

 

[Harvard]

If your meter measures capacitance you could try to also measure C from X to Ground and Y to Ground. To get the best data, measure these C readings of both the RV and of just the 50 Amp cable (ie cable unplugged from the RV)