Just washed my TM - now the TM trips my home GFI

[ShrimpBurrito]

Thanks for everyone's help while we were on the road. We made it back home, although with a few more things needing repair, and the GFI gods are still working against us.

Mike - Thanks for the suggestion. I checked that fridge compartment, and especially the outlet in there, and everything is bone dry. No evidence that water has been in there anytime recently.

Chip - I tried a new 30A to 15A adapter plug. The GFI still trips.

Harveyrv - Good note about the neutral and hot being switched. However, according to the referenced article, most GFI outlets interrupt both the hot and neutral as an added safety measure to protect against the reversals you found in your building.

I read the very informative explanation on the website rumbleweed posted, but I am still confused as to how the GFI can trip with the main breaker off if there is a neutral-ground short. I understand that the breaker only interrupts the hot wire. But with the main breaker open, the current on the hot wire, on both sides of the smaller breakers on ALL the AC circuits (fridge, A/C, outlets), should be exactly ZERO. So if the GFI is tripping with the main breaker off, and it's a neutral ground short, that means there is current in some neutral wire, right? (Since the GFI only trips when the current in the neutral and hot is different.) How is that possible? I read Bill's post referenced above, where he says:

But how can the neutral wire have a different potential from the ground wire, if they are bonded together at the far end? Consider this. The outlet that you plugged the TM into is not the only outlet on that circuit. There are other outlets along the way, and those outlets may be providing power to other loads (devices). Maybe a lamp, maybe a radio or a TV - doesn't matter. As a result of those loads, there is current flowing out through the circuit's black/hot wire, and back through the white/neutral wire. Like all wires, the neutral wire has a small resistance - and the current flowing through that resistance causes a small voltage to be generated down the length of the neutral wire. Now of course there is no current flowing in the ground wire, so no voltage is generated there. The neutral and ground have the same potential at the service entrance - but a slightly different potential at the far end, which is in the TM. So if you connect them together in the TM, a small current will flow in the neutral. And since a corresponding current doesn't flow in the black wire, the GFI pops.

But there was no current being drawn from the GFI that is tripping other than the TM. I have 220v going out to the garage to supply the dryer. 110v splits off of that and goes to the GFI, which in turn supplies power to 2 other outlets and overhead lights. Nothing else connected to those outlets was drawing any power (no standby devices out there), and the overhead lights were off.

Interestingly, that article reference above specifically stated that the NEC has excepted 30A and 50A RV outlets from having a GFI. I presume that means if you're at a campground where the power doesn't have a good ground, that could be particularly hazardous.

Dave

[Bill]

But there was no current being drawn from the GFI that is tripping other than the TM.

Although my paragraph you reference didn't explicitly say so (it was getting mighty long and dry already!), the neutral current that causes the imbalance does not have to be flowing through the GFI. It can be flowing before the GFI, and still cause the problem. In other words, any 120-volt load before the GFI could cause the problem. But it really doesn't sound like this is what you are experiencing, since you have used this same outlet before, and haven't done any rewiring on the circuit.

Next step is to unplug the refrig in the TM. By doing so, you open both the hot wire and the neutral to the appliance. This is unlike turning off the circuit breaker, which opens only the hot lead. If this doesn't cure the problem, do the same thing to the A/C - since it is a side A/C, I think it is plugged in under the kitchen counter somewhere.

If this doesn't work, you are left with the converter, which is more difficult since it doesn't unplug. If you are an electrical masochist (like I am), disconnect shore power, figure out where the neutral comes into the converter, and disconnect it - not the hot wire, just the neutral. Be real careful while doing this, and be sure to tape up the flopping neutral wire so it can't contact anything. Now reconnect shore power and see if it still pops the GFI.

We have at least one documented case here on the board where turning off the power (hot lead) to a bad water heater didn't stop the GFI from popping, but disconnecting the white wire from the water heater did fix it.

Otherwise, the next step might be to try plugging the TM into a different GFI-protected outlet, or even changing out the GFI if you have a spare. Sometimes they do become hyper-sensitive.

Bill

[ShrimpBurrito]

Originally Posted by Bill

Next step might be to try changing the GFI, or plugging the TM into a different GFI-protected outlet. Sometimes they do become hyper-sensitive.

Bill

I'm not sure why either of those steps would make any progress -- other devices work fine in this GFI outlet, and the TM tripped a separate GFI -- this one at a campground. So the problem seems isolated to something in the TM, don't you think?

And you're right, I haven't done any rewiring to the house.

Dave

If there is an incorrectly connected neutral and ground wire somewhere in the system, the neutral and ground can be at different potentials causing a small amount of leakage current to flow through the neutral while no current flows through the hot . Remember the GFI is designed to trip on a very low current difference. Use a tester to make sure that the outlet in the house has the ground and neutral not reversed. then check the TM to see that the there is no voltage between the neutral and ground.

Tangental, but related - the reason that there are no GFIs on the 30 and 50 amp RV park outlets typically, and why the NEC exempts them is that large motor loads (like your A/C unit) can sometimes trip GFIs when there is no safety risk.

[ShrimpBurrito]

Wow, Bill. Thanks so much for posting that clear explanation on neutral-ground faults in the "TM Info you won't find anywhere else" section, along with the diagrams. Really over the top. The diagrams especially helped clear things up -- I just could not understand how the TM could be tripping the home GFI if the TM main breaker was off.

I am happy I now what the problem is, but hopefully it won't take too long to find the short. It could be anywhere.....since it's been 2 weeks since I washed the TM and I first realized I had a problem, I feel more and more that the water was just an unrelated coincidence. I went on a trip AFTER the last successful time I plugged it in, and 2 weeks ago was the first time since then when I tried to plug it in again. So perhaps something happened on that trip to make a short.

I'll post back when I make some progress.

Thanks again!

Dave

We had the same/similar problem with our 2720SD, just purchased it. The circuit breaker outside our home kept tripping, even when everything was off. The only we had run was the heater and the lights. Not sure what the problem may be, it also was after a prolonged rain storm. It is now winterized and put away but will have to deal with it in the spring. ? maybe it will fix itself??? any suggestions etc appreciated

[Bill]

Frustrating, isn't it? Going back to an earlier post, the next step is to unplug the appliances and see if one of them solves the problem. As you can see from the diagrams I posted, this is different from turning off the breaker because it interrupts not only the hot lead to the appliance, but also the neutral and ground leads.

Bill

[ShrimpBurrito]

Well, with the help of Bill's explanation and fabulous diagrams, and some guidance from my Dad (who is an EE), we solved the problem. As it turns out, the GFI fault and me washing the roof were merely coincidental.

We started troubleshooting by testing the resistance between the hot and neutral blades of the 30A plug on the TM against the ground pin on the same plug. With the TM main breaker off, one of the blades shorted to the ground pin. Then my Dad walked into the trailer and the short disappeared. Then he walked to the front of the trailer and the short reappeared. Both of us immediately started having visions of having to rip up the floor in search of an elusive short, and an intermittent one at that.

Next we wanted to determine if the blade that was shorted was the hot or neutral. We presumed it was the neutral, after looking at Bill's diagram, because the GFI would trip with the TM main breaker off, but we wanted to be sure. I pulled out the converter from the wall, and put one lead of the ohm meter on one of the blades of the plug, and the other lead on the other side of the cord where it attaches to the converter. It was the neutral wire.

There are 4 (if I recall correctly) sub-main AC circuit breakers in the TM: converter, refrigerator, GFI, and A/C. We disconnected the neutral wire to the first breaker from the bus, and plugged the TM into the GFI of my house. By disconnecting the neutral wire, the home GFI would not trip if the short was in the circuit we just disconnected. But it did, so we knew the fault was in one of the other circuits. We reconnected that neutral, and repeated this process until, of course, the very last circuit: the air conditioner.

With the neutral wire to the air conditioner circuit disconnected, the GFI did not trip. So somewhere in that circuit, we concluded, the neutral wire is touching either the ground wire or something else that is grounded to the frame.

Since I have a side-mount air conditioner, I immediately thought that perhaps there was STILL water in the outlet the A/C is plugged into, as a result of my washing. A stretch, since we drove 1200 miles, much of it through the desert, and almost 2 months sitting in a semi-arid climate here in LA. But I couldn't think of anything else. Then we thought back to the intermittent problem where the short would disappear and reappear when walking from the back of the TM to the front. More visions of ripping up the floor came to mind. I also thought it was possible that I ripped a wire open when I snaked a new wire in the tunnel under the bathroom for my Link 10, but I did that almost a year ago, and we'd had many trips with the TM since then and the GFI never shorted.

We decided to eliminate anything obvious first, and pulled out the A/C unit to see if there was something obvious that was causing the problem. As it turns out, the problem was obvious. We were lucky. The wire to the A/C unit comes out the bottom and towards the front -- in fact, so far to the front that if you kneel on the floor and look underneath it it, you can see it while it is installed. The it runs UNDER the A/C unit towards the wall where it plugs into an outlet hidden by the unit itself. The A/C unit had worn down the insulation of the wire, and was shorting the wire to the A/C chassis, which is connected to the ground wire. VIOLA! No ripping up the floor! By walking from the back to the front of the TM, we presumably flexed the cabinets in some way for the A/C to sag and make the short.

Now that we identified the problem, we wanted to fix it so it would never happen again. That wire had to be rerouted. The bottom is out for obvious reasons. The side of the unit is out because then the unit will not fit into the hole. The back is out because it is very crowded with coils, which get hot, and the wire is only rated to 60 C. That leaves the top. In my unit, there ended up being barely enough room. We bought a 3/8" right-angle clamp for armored cable (couldn't find one for romex), wrapped the A/C wire in some scrap rubber to protect it from some ridges in the clamp (which ordinarily brace in armored cable), and mounted it on the top of the A/C. A spade bit will cut through sheet metal like butter if you don't have a punch.....

If you end up doing this, take note of the C-channel on the bottom of the A/C. The combined height of the A/C, C-channel, and cable clamp will not fit in the opening -- only the A/C and C-channel or A/C and cable clamp will fit. So the cable clamp has to be installed behind the C-channel. The cable clamp will go in the opening first, then the C-channel.

This is a potentially life-threatening condition. We rarely ever camp with hookups, but those electrical hookups I have seen don't have GFI's. Thus, this condition would not have been brought to our attention. And if we would have ever plugged into a campground that didn't have a good ground, or used a 30A to 15A adapter and then a 3-prong to 2-prong adapter, we could have been electrocuted.

I plan on replacing the TM main breaker with a GFI breaker as an added safety measure.

Thanks to everyone for all their suggestions, and especially to Bill for taking the time to write out such a thorough explanation and sketch those diagrams. They were VERY helpful.

Dave

[Leslie & Nick]

Good catch, Dave!!!

The picture of the abraded AC wire said it all. Constant rubbing from the air conditioner frame would certainly wear through the insulation in time. I have a side mounted AC too, and I think I'll check the wire routing to make sure it's not running underneath the AC chassis. Glad you found it before something bad happened

I guess this particular type problem might not be as far fetched as one might think. We had a similar problem with a low voltage thermostat wire in a motor home we rented many years ago (shortly after the invention of the wheel). We wondered why we were suddenly getting no heat. It was so cold, dripping water froze in the kitchen sink (and this was in Tallahassee in December). To make a long story short, the thermostat wire was pinched under the furnace chassis, and was shorting out. An RV dealer that we found, quickly located the problem - they must know what to look for because it happens so regularly!