Diplomat with "hot skin"

[rgreen45]

I'm working on a 2012 Diplomat and the customer complained of getting a shock when they touched the coach exterior when wet. A hot skin test revealed 40V. I've traced the cause to the invertor subpanel but as of yet haven't found the root of the problem. I took the invertor out of the loop so it's not suspect.

As you go down the row turning off breakers on that subpanel, your voltage reading diminishes. Once all are off, minimal reading <3v. I've inspected closely in the panel box for a wire out of place and haven't found any.

Anyone had this problem before?

[Pds47]

Worked in the mobile home industry years ago and we would get a hot coach once in awhile. mostly caused by a screw that hit a wire under the skin

[RustyJC]

Tighten all your neutral connections in the breaker boxes as well as all grounds. This typically occurs when you have return current flowing through the ground conductor instead of the neutral conductor due to a high resistance or open neutral. Since the RV frame is connected to the RV's ground circuit, it assumes a voltage potential with reference to true earth ground. Typically, the user will feel this when he's standing on the ground (wet ground, especially) and touches the skin/door handle/etc. of the RV. Remember, neutral and ground circuits are NOT bonded together in the RV's power distribution panel - that happens somewhere back in the campground's power distibution system where an earth ground will be located; therefore, you can get some conductor voltage drops before the ground current finds its way to earth.

It could also be caused by a heating element in the fridge or water heater that has a high resistance short to ground IF these element circuits are not GFI protected.

Rusty

[Capn_Dave]

Well if you put a meter on it and it had 40A on the outside of the coach and you were ground, you would be dead, cooked, fried. Currents of 100 to 200 Milliamps are lethal

[DennisZ]

I would look at the incoming power and measure at the circuit breaker box to see if you have balanced power between each incoming power leg and the neutral leg. If they are the same within a volt or so, put a load on one leg like turning on an AC unit and measure the voltage again. If the loaded leg goes way down and the unloaded leg goes up, you have a neutral grounf=d issue, this same condition will give you a "Hot Skin" condition. I would suspect this condition especially since you say the voltage goes down with every breaker turned off.

If the issue were with a screw puncture, the condition would go away completely when the effected circuit breaker was turned off.

I had a friend that had a bad neutral in his power cord reel, caused him all kinds of problems.

Dennis

[halfwright]

Read the post,Dave. He said 40 VOLTS.

[terry735001]

Originally Posted by RustyJC

Tighten all your neutral connections in the breaker boxes as well as all grounds. This typically occurs when you have return current flowing through the ground conductor instead of the neutral conductor due to a high resistance or open neutral. Since the RV frame is connected to the RV's ground circuit, it assumes a voltage potential with reference to true earth ground. Typically, the user will feel this when he's standing on the ground (wet ground, especially) and touches the skin/door handle/etc. of the RV. Remember, neutral and ground circuits are NOT bonded together in the RV's power distribution panel - that happens somewhere back in the campground's power distibution system where an earth ground will be located; therefore, you can get some conductor voltage drops before the ground current finds its way to earth.

It could also be caused by a heating element in the fridge or water heater that has a high resistance short to ground IF these element circuits are not GFI protected.

Rusty

hes sade he had a inverter in the system so yes there is a neutral to ground auto circuit in the RV in the system

all so the gen set well run on this same circuit to do its neutral to ground

if the circuit is holding in the closed .. you could be seeing the 40v from the hot side flowing in to the gen and back out the ground showing your 40v at all times

the circuit is like a at home well water pump relay and you know what happens when ants move in to it

[mahon1993]

Had the same problem with my first coach. Problem was a screw thru the romex. Trace it by turning all the breakers off and see what you get. Process of elimination.

[rgreen45]

Thanks all for the advice. Here's the latest ......

I tested the two incoming legs and they were within 2 volts. I turned on the AC and that put them 10 volts apart.

I tested between the ground bar and the common bar and the reading is around 33 volts. Baffling!

Now it really gets good. 6 breakers on the main panel are "double" breakers. If I shut them off and test from the hot lead (breaker screw) to common, one throw will show about 2v and the other 22v-30v. Test from hot lead to ground and the scenario is reversed. The last breaker in the main row is the output to the invertor. It's a single throw. Cut it off and all is well.

Next, while reading the 33v between common and ground bars, I started turning off breakers on the main panel. Some made it fluctuate a bit but even with all off I had 33v-34. Do that same thing with the breakers on the invertor panel and with each one you shut off, the voltage drops a bit. When all are off, it's under 3v. Turning off either the breaker on the main panel feeding the invertor subpanel or the main breaker on the invertor subpanel does the same thing of course.

All these breakers are in the same box of course. I'm beginning to suspect the transfer switch wiring and the reason it effects the invertor subpanel is because the breaker feeding the invertor is at the end of the "main" line.

Also, I haven't started the generator to see if the same problem(s) exist while on genset power. That'll be the first thing I do in the morning.

Thanks again for all your help.

[DennisZ]

Ray
The 10 volt difference is enough to peak my interest, the big question is did the leg with the AC go down and did the other leg go up? if the unloaded leg went up, you have a bad neutral if it didn't you have other issues. BTW, I've been thru this same problem with a couple of houses and a building I store my motorhome in, very common.

Dennis

[rgreen45]

Dennis, the leg with the AC went down about 6 volts and the other went up a couple. I had like 122v and 124v initially and after bringing on the AC it went to 116.7v and 127.2v.

[ahicks]

Originally Posted by RustyJC

Tighten all your neutral connections in the breaker boxes as well as all grounds. This typically occurs when you have return current flowing through the ground conductor instead of the neutral conductor due to a high resistance or open neutral. Since the RV frame is connected to the RV's ground circuit, it assumes a voltage potential with reference to true earth ground. Typically, the user will feel this when he's standing on the ground (wet ground, especially) and touches the skin/door handle/etc. of the RV. Remember, neutral and ground circuits are NOT bonded together in the RV's power distribution panel - that happens somewhere back in the campground's power distibution system where an earth ground will be located; therefore, you can get some conductor voltage drops before the ground current finds its way to earth.

It could also be caused by a heating element in the fridge or water heater that has a high resistance short to ground IF these element circuits are not GFI protected.

Rusty

Rusty, regarding the bonding within the RV's panel, I'm assuming there's a good reason for this, but it's beyond me at the moment? Why is that?

If this is one of those questions that's been discussed to death, a link to it would be fine. Thanks, -Al

[RustyJC]

Because, to avoid ground loop currents, the neutral is bonded to the ground and then grounded to earth only at the campground shore power primary power distribution panel. The RV is downstream of this panel and is considered a connected load, and its AC power distribution panel is considered a secondary panel and, therefore, not grounded to earth nor is neutral bonded to ground within that panel. That's why your shore power cord has separate conductors for neutral and ground going back to the campground hookup.

Rusty

[gio8856]

Sounds like the problem is in your shore power circuit or cord. but cords just don't go bad.