Electrical gremlin--shorting to ground - Montana Owners Club

David and Jo-Anna · 08-02-2009, 09:11 AM

While helping me remove a faulty landing gear on Friday, John Kohl noticed what appeared to be some electric juice in the frame that his body was shorting to ground. When we checked with a multimeter, we found what appeared to be 12v at the frame in the area of the front landing gear. Subsequent investigation revealed more potent juice--about 35v of DC juice and 85v of AC juice in the area of the front landing gear. There doesn't seem to be a lot of current there as I am not getting a substantial shock when I use my body to short the juice to ground, and we are not popping any breakers or fuses. Question is--what's causing this electrical leakage into the frame.

We checked several things and couldn't nail the son of a gun. I tried switching to another campground power pole--no change. Pulling the main DC voltage fuses in the rig also had no effect. When we cut the main AC breakers in the rig, the juice in the frame disappeared--which seems to say the problem is in the rig, not in the campground power. We shut off all the individual AC breakers and then turned them back on one by one. It seemed that every time a breaker was turned on, there would be an increase in the voltage level detected in the frame. With some circuits, the voltage increase was small. With several breakers (converter, kitchen, entertainment center, and living room slide out), there was a bigger increase when the breaker was turned on. All the increases seemed to be cumulative--as more circuits were turned on, the higher the voltage in the frame increased. FYI, we have a 2007 Montana Big Sky 340RLQ, which is the same floor plan as the 3400.

Any suggestions as to what is causing the problem and/or what we can test next? And thanks in advance for all the good help I know this forum will be able to provide.

8.1al · 08-02-2009, 09:39 AM

I am electrically challenged but this sounds to me like a ground problem. Hopefully someone has a more definitive answer

SlickWillie · 08-02-2009, 09:54 AM

Quote:

quote:Originally posted by 8.1al

I am electrically challenged but this sounds to me like a ground problem. Hopefully someone has a more definitive answer

Agreed. I think I would start out checking the power cord ground wire. Then the ground buss in the distribution panel in the RV. If that ground is good, it should have a heck of a lot better path to ground than the human body.

Pete Hanson · 08-02-2009, 10:16 AM

I ran into a similar thing and after checking the Monty outlets with a circuit tester I found not only reversed polarity but an open ground as well. The open ground was not in the Monty or the umbilical cord but was at the power pole. Once fixed we were good. The circuit tester i used was the kind that plugs into your outlets and little lights tell you if its ok or not.

Countryfolks · 08-02-2009, 10:30 AM

It seems to me that someone else had a similar problem some time back. I think it turned out to be a loose/broken ground connection at the 50A input receptacle. It may be in the cable.

The voltage is a result of the way all RVs are wired. They have what is called a floating ground. The neutral and the ground are separate. This will allow a potential voltage difference between the RV and the earth [ground]. The voltage will go to ground through you if it cannot go through the ground wire in the cable.

awaywego · 08-02-2009, 10:47 AM

I had the same problem several years ago and found when they wired the pedestal in the campground they hooked the hot to the neutral and neutral to the hot. Since the neutral was grounded the voltage was feeding through the trailer to ground.
Use your meter to check the plug at the pedestal with the Monty unpluged and see if the neutral wire is hot to ground.
I stuck the ground lead of the meter into a damp spot on the ground and the other to the trailer and read 50+ volts.
Just one more thing to try.

David and Jo-Anna · 08-02-2009, 10:50 AM

Couple of other things I forgot to mention. I have checked the power pole and a number of outlets with my little three-light plug-in circuit tester with no indication of any open ground or other problem. Also checked the power pole with my multimeter--but not sure if that would show a floating ground. I also checked all the connections in the AC circuit breaker box--all the connections were tight.

How do I check out the ground buss in the AC panel to make sure that is a good ground?

sreigle · 08-02-2009, 10:55 AM

I agree with Pete and the others who mentioned an open ground or similar problem. We also use the tester with the lights, like Pete.

Last Fall we visited friends in NY and parked our rig in their yard. We connected to a 20amp outlet on a shed. I neglected to check the power as I normally do before plugging in the rig. Soon as I touched our rig and got that electrical buzz I knew that was a mistake. The tester then showed an open ground on that circuit.

These testers are less than five bucks at Walmart, by the way.

Exnavydiver · 08-02-2009, 11:01 AM

Dave, you can always check it like a 9 volt battery, with your tongue. If your face bursts into flame then there is a problem, if your ears just flap then close the window as it is too windy. If you fall over dead then H. John Kohl made this post... Dave

NCFischers · 08-02-2009, 11:27 AM

David,
If it was me, I wouldn't try Dave's solution. I agree that you probably have a loose or open ground. Check both ends of your power cord and the pedestal. Also, check the inlet box on the trailer where the power cord plugs in.

Exnavydiver · 08-02-2009, 12:01 PM

I helped Dave with that problem yesterday, I wet the ground with some salted water and stuck one lead from the VOM into the wet ground then touched the other end to the frame. In DC mode we had close to 12 volts sometimes and 4 or 5 other times. When I switched to AC mode we got 85 to 87 volts. As Dave shut off various breakers the voltage dropped a few volts with some and as many as 30 volts with others. The lowest voltage I saw was around 28 to 29, it varied the whole time. When He killed the main at the pedestal the AC voltage went away but back on DC mode we were still seeing as few as 2 and as much as 10 volts DC... Dave

Countryfolks · 08-02-2009, 12:11 PM

David;
Remove the 50A connector on the trailer. The bad connection I was referring to is there, not the power post. I don't know if those low cost, three light, receptacle testers will show a bad ground under these conditions but try one inside the 5er. The floating ground is a concept that implies separate voltage potentials, the earth ground being zero and the floating ground [the RV] potentially being at a different level.

Are your front and rear levelers on blocks? If they are, try removing one of the blocks and putting the pad into direct contact with the ground. If the voltage goes away the problem is in the rig, a bad or poor ground through the power cable.

You could also check that the ground connection in the front compartment is good, and the one on the rear of the fuse panel is good.
edit: Try a different power cable also if one is available.

David and Jo-Anna · 08-02-2009, 01:41 PM

Lots of good suggestions--except for Dave's proposal that I stick my tongue across the voltage. LOL!!!!!

I swapped out the power cord for another one--problem still there. The connection from the plug into the rig looks real good--and it was put in new less than a year ago. But that's just a visual check--anything other than a visual check that I can do on that connection point? I've tried my cheapo three-light tester at the power pole and in outlets in the rig and is does not show any open ground or any other problem.

Tried my cheapo multimeter and checked the 30 amp power outlet at the pole. Assuming I got the hot and the neutral correct (ground was at 12:00, and I assumed neutral was at 4:00 and hot was at 8:00--is that correct?), I got 122v between hot and neutral and also 122v between the hot and ground holes in the outlet. Get no voltage between the ground hole in the outlet and actual ground in the dirt. Is that what it should be showing?

My rear stabilizers have one pad in the grass and the other pad resting on a plate with metal strips in it that I got from Roto-Chock as lightening protection--supposed to create a really good path from the stabilizer pad to the ground below. When I lower the rear stabilizer pads to the ground, the AC voltage reading on the frame drops from 85V to 25v, so the grounding by the pads has an effect--but does not take the voltage on the frame all the way to zero.. Go figure!!!

How do I check to see if the "ground connection in the front compartment is good"? How do I check to see if the ground connection in the rear of the fuse compartment is good? Do I have to run a wire out the window and stick it in the ground?

Dave--in playing with my cheapo multimeter after you left this morning, I realized that the DC voltage off of the rig was reading low because I had it set on the 20 volt scale, and it was getting overloaded. Once I kicked it up to the 200v scale, I started getting the DC voltage reading at 35+ volts. I can't understand where I'd get that much DC voltage--I thought all I had running around anywhere in the rig was 12-13v DC. Color me puzzled!! Hope I don't get so frustrated that I try your recommended "tongue test." LOL!!!

Countryfolks · 08-02-2009, 03:26 PM

Its like checking and cleaning battery connections. The connections could be loose or dirty.

Where are you placing the meter probes when you're taking these measurements?

You might try unplugging your converter. If I remember right it plugs into a standard outlet.

H. John Kohl · 08-02-2009, 03:50 PM

Quote:

quote:Originally posted by David and Jo-Anna

Lots of good suggestions--except for Dave's proposal that I stick my tongue across the voltage. LOL!!!!!

-- snip --

Dave--in playing with my cheapo multimeter after you left this morning, I realized that the DC voltage off of the rig was reading low because I had it set on the 20 volt scale, and it was getting overloaded. Once I kicked it up to the 200v scale, I started getting the DC voltage reading at 35+ volts. I can't understand where I'd get that much DC voltage--I thought all I had running around anywhere in the rig was 12-13v DC. Color me puzzled!! Hope I don't get so frustrated that I try your recommended "tongue test." LOL!!!

David. I would not worry about the DC voltage until you have eliminated the AC voltage. Focus on the key one. I believe your DC voltage may be a "blead over" from the AC side. The DC side may be rectifying some of the AC and giving you a false DC reading.
Let us know what you find.
Cheers,

Jetson · 08-03-2009, 03:03 AM

I had similar experience with my house after Hurricane Ike last year. The ground wire was ripped out but not the 2 hot wires to the house. It would shock you in the shower if too much was running, like the central air. I checked voltage with my RV plug in meter. It would vary from reading too low to reading too high, like 80 to 140 volts if you turned on the microwave. I used my truck jumper cables to reconnect the ground wire to the weatherhead for over a month until the power company came out to reconnect it.

The point of this is that the lack of a return line (ground) will cause all sorts of weird readings like you have been getting. It could be lack of ground in your rig or the campground.

ole dude · 08-03-2009, 03:22 AM

Where your shore power cord plugs into the trailer, have you pulled that plug out of the trailer and checked that all those connections or tight. You will have to get to the back of that female plug to check. Have seen loose ground wires there that caused similar problems to yours.

firetrucker · 08-03-2009, 06:39 AM

If each additional current draw increases the leakage voltage, that suggests a problem with the main ground, and maybe even the neutral.

If you can, plug your power cord into other pedestals, even if you have to adapt the 50 to a 30.

Pull your panel and check the tightness of the ground and neutral connections.

Finally (we would hope), check the connections on the 50 A power receptacle on the rig.

If all that fails to locate the problem, and it were me, I'd completely bypass the main (from the receptacle to the panel) by turning off the main breaker, turning off evverything in the trailer, and plugging the pedestal into one of my outlets. Like Mythbusters says, this is not something you should do at home, and should only be done by someone with years of experience.

Bob

David and Jo-Anna · 08-03-2009, 01:44 PM

OOPS!!! Apparently an update I thought I had posted before going off line this morning never made it to this thread. More Gremlins!!! The update concerned the disappearance of my stray voltage.

Last evening, Al Stevens ("Countryguy") and I checked the connections where the 50 amp receptacle plugs into the rig. The connections were tight--the only screw movement I got was a half turn on the screw holding the neutral, but that connection felt tight even before I was able to turn the screw a little. After reassembling the connector, and checking a few other things (but not finding anything out of order), we turned the power back on and took further measurements. Initially, with the rear stabilizer legs planted on the ground, we got 18v of AC compared to the 25v of AC we had gotten before checking the rear connector. I then raised the rear stabilizers and expected the voltage to climb up towards its earlier readings of 85v. Instead, the voltage dropped to 0.6v, and nothing we did thereafter could cause the higher voltage to return.

I can't believe the little tweeking I did on the rear connector cured the problem. Instead, I suspect that I now have an intermittent problem. I was hoping that bouncing down the road today might bring the problem back, but no luck--all I get in this new campground is 1.6v AC, and that doesn't change whether the rear stabilizers are up or down in the damp sandy soil at this campground. Go figure.

I'm wide open to suggestions at this point as to what to do now.

P.S.--Bob, before my voltage disappeared, I had swapped my power hookup to another power pedestal without any drop in the voltage reading I was getting. I've also checked my inside power panel, and all the connections were very tight.

PPS--I have been taking most of my readings from the bare metal on the (retracted) curb side front landing leg. To get a good ground on my multimeter, I stick a screwdriver into the ground and stick the other probe into the dirt next to the screwdriver and then pour some saltwater over the tip of the probe to make sure it has good ground contact. That technique was giving me reliable, repetitive results until the voltage suddenly disappeared.

carlson · 08-03-2009, 06:35 PM

Dave,
You have described a problem that I have had with our 2005/3400RL.
It is the same problem to a tee.
Did everything possible, even cut off the end of a $130.00 pre-made power cable, where we thought the problem was, wrong!!!!
Sorry about the bad news, ours also went away, only to return when you lease expect it.
Again we tried everything possible, the problem in not at the power pole, or the plug, it is in the rig.
Sometimes there and sometimes not, and when you lease expect it, it will give you a little bite.
Sorry to not have any suggestions to correct it, it is just one of those great things about have water and electricity, they take the path of lease resistance, sometimes you are the ground!!!

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