Hot skin

[Casey Freswick]

I have a hot skin problem. I used my volt meter and determined there were about 80 volts going from the skin of the trailer to ground. I became the ground working on the step on a project that resulted in a slight shock when I put a bare knee on the ground. Being bare foot and touching the door knob also produced a shock. The second about the kind of shock I had as a kid touching an electric fence. The problem was in the outlet. Neutral to ground had about a 15 volt read. Ground to hot: 90 volts. Neutral to hot: 120 volts. Everything worked on this 15 amp outlet, but the hot skin continued. When I used my generator, no hot skin. We needed to use our AC so needed a 30 amp 3000 watt power source. So here is the question.

Should my TM have hot skin with a bad connection or should the trailer ground fix the problem? Do I have two problems or one? I checked the voltage when plugged into my generator at the circuits panel my ground to neutral is 0 volts. My ground to hot is 120 volts. My Neutral to hot is 120 volts.

I do not know enough about electrical stuff to really answer my questions. DO I have good ground problem or is it just the bad outlet I was using.

[Casey Freswick]

I checked all the extension cords. Everything was in good order.

[Larryjb]

I need to ask which outlet were you checking.

Were you checking the pedestal outlet with no connections?

If you were checking this outlet, there is definitely an issue with the outlet. The ground and neutral should be bonded at the electrical service for the campground, but it shouldn't be bonded at the pedestal. If you have a voltage difference between ground and neutral, the neutral may be electrifying the skin of your Trailmanor.

Were you checking one of the TM outlets?

If you were checking this outlet, there are too many variables at the moment.

You can take a look here as well: https://www.rvtravel.com/rv-electric...pground-power/

Bill had a good description of neutral-to-ground issues in post 27:
https://www.trailmanorowners.com/for...nd+bond&page=3

[rickst29]

Originally Posted by Casey Freswick

I have a hot skin problem. I used my volt meter and determined there were about 80 volts going from the skin of the trailer to ground. I became the ground working on the step on a project that resulted in a slight shock when I put a bare knee on the ground. Being bare foot and touching the door knob also produced a shock. The second about the kind of shock I had as a kid touching an electric fence. The problem was in the outlet. Neutral to ground had about a 15 volt read. Ground to hot: 90 volts. Neutral to hot: 120 volts. Everything worked on this 15 amp outlet, but the hot skin continued. When I used my generator, no hot skin. We needed to use our AC so needed a 30 amp 3000 watt power source. So here is the question.

Should my TM have hot skin with a bad connection or should the trailer ground fix the problem? Do I have two problems or one? I checked the voltage when plugged into my generator at the circuits panel my ground to neutral is 0 volts. My ground to hot is 120 volts. My Neutral to hot is 120 volts.

I do not know enough about electrical stuff to really answer my questions. DO I have good ground problem or is it just the bad outlet I was using.

This entire post is dedicated to verifying safety within the TM , WITHOUT TOUCHING the more likely mis-wired 30A outlet.

Being "OK" on the generator is only definitive if you again test the TM frame (or skin) versus true earth ground. The generator "grounding" (safety) lead floats along with the TM frame, and could theoretically be non-zero, even with the Generator running and showing the voltages you describe.

You need to FIRST test between safety ground (bare/green wires) and neutral (white wires), at the 120V TM panel with no 120-VAC service plugged in - no "campground" plugin, and no generator either. Test for resistance. If it's not infinity, then there's a fault within the TM (somewhere).

Disconnect the Inverter leads/plugs from 120-VAC, including any transfer switch.

Then check the same for "hot" (black 120-VAC) service at the panel. With all circuit breakers in active "closed" position but no power input to the TM, and no appliances connected to outlets (and disconnect the Inverter!) Black to White and Black to Green/Bare/TM "skin" must both be infinity.

Then plug in the Inverter DO NOT power it up. Test all 3 combinations again, they should all be infinity. Then power up the inverter and carefully! test one more time. Wear rubber gloves and be super-aware of WHERE YOU ARE HOLDING THOSE PROBE ENDS! With no appliances connected or running, resistance should again be infinity between each combination of leads.

If you've got a transfer switch, it could also be involved.

[ShrimpBurrito]

Casey - Is your air conditioner on the roof or mounted in a cabinet by the oven?

Dave

[Casey Freswick]

On the roof.

[rtcassel]

https://www.trailmanorowners.com/for...ter#post137014

[Bill]

I’m a little late to the party, but Oldstick, thanks for your confidence. I’m pretty much in line with what has been posted so far. Casey, you need to answer the question Larry asked on Post #4 - when you say you checked “the outlet”, which outlet did you check? The one on the power post (or in your house or garage), or one of the outlets in your camper?

Your next step should be to try a different extension cord, plugged into a different outlet. Then, as Oldstick suggested, you should get one of the little three-light testers like the one in this picture. It is cheap, and will answer many of our questions as we try to help you.
https://www.trailmanorowners.com/for...&pictureid=452

Since we are talking about commercially-supplied AC power, it wouldn’t hurt to have a short review of the word “ground”. Please don’t groan and turn away - it is the heart of the dangerous problem Casey is asking about.

In AC power systems, there are two different kinds of grounds. They should have different names, but for whatever reason, they don’t. The first is properly called Earth Ground. As the name implies, this is the earth - the dirt under your feet. It includes rocks, trees, puddles, lakes, and any other conductive object that is in contact with the earth. In your electrical supply system, there is a long copper stake driven into the ground, with a wire attached to it. This stake is the actual Earth Ground, and the wire is the connection to Earth Ground.

The second is called the Safety Ground. This is all of the metal in your Trail Manor. The inner and outer skins of the trailer, the frame, the hitch, are all connected to the Safety Ground. An AC outlet has three openings. The small round one is connected to the safety ground, and through this, the metal parts and case of all your plug-in appliances and electrical tools are connected to the safety ground. All of these parts are electrically connected together, and that whole connected mass is called the Safety Ground. The TM's Safety Ground is carried out of the trailer on the third wire (green) inside the TM's big black power cord, and the third (round) pin in the big black power plug makes the connection to the Safety Ground in the power source.

The purpose of the Safety Ground is to collect any stray voltage that appears on any metal part of the TrailManor (no matter how it got there), then carry it away and shunt it into the earth, where it is harmless. To do this, the Safety Ground is connected to the Earth Ground at a single designated location. [For reasons that are not relevant here, only a single connection is allowed, and that is within the electrical supply box. Multiple connection points are not allowed.] An important thing to know is that under normal circumstances, the Safety Ground NEVER carries any current. It is an emergency path only, designed specifically to protect you, the user, when something goes wrong.

If I have explained all this well, it should be apparent that that there cannot be a hot skin as long as the Safety Ground is connected to the Earth Ground, because the skin of the trailer is connected to the Safety Ground, which is connected to the Earth Ground, and Earth Ground shunts away the voltage that is making the skin hot. If you have a hot skin, it means that the two grounds are not connected. Casey, you have a hot skin, which means that you need to find and correct the disconnect.

In the world of RVs, there are two places where this fault is almost always found. The first place is the outlet that supplies power to the trailer. It might be on campground power post, or in your house or garage. A shade-tree electrician could have mis-wired the box, or the wires could have corroded and come loose inside the box. That is why Larry’s question is important. The second place is the extension cord that brings power to the trailer. You said that you checked the extension cord. How did you check it? Is the cord a three-wire cord or a two-wire cord? Are all three pins present on both ends of the cord, or was the third (round) pin cut off the plug? Is the cord in the same condition as when you got it from the store, or has the plug or socket been replaced? Has the cord been cut or spliced? Have you used a 3-prong-to-2-prong adapter to plug it into a two-prong outlet? We need answers to all of these before we can go much further.

Finally, it is important to realize that a hot skin requires two faults. No single fault can cause a hot skin. I have pointed out that an open ground connection allows a hot skin to exist, but it doesn’t tell you anything about what is causing the hot skin. Somewhere there is something that is leaking the voltage onto the trailer skin in the first place. You need to find it, and fix it. This is a separate issue from the ground problem.

Generators are also a separate issue, not related to hot skin, and we can take them up later if anyone wants to do so.

Bill

[Bill]

Originally Posted by rtcassel

https://www.trailmanorowners.com/for...ter#post137014

Tim -

In the linked post, Bruce wrote

A burned out heating element is the major cause of hot skin in RVs.

It has never been clear to me how a burned-out water heater element could result in a hot skin. A water heater element is nothing but an electrically-heated wire inside a waterproof tube. If the element is turned on without water, it can get so hot that it burns through the tube, which then sags down, and now the live wire can touch the inside of the metal tank. But the metal tank is connected to the safety ground (see previous post), and so the fault current is shunted to earth ground, which trips the circuit breaker. This is a good example of how the safety ground is supposed to work, as well as what can happen if the safety ground is disconnected from the earth ground.

At any rate, I don't think there is a need for Casey to spend a lot of time investigating the water heater as a possible cause of the hot skin problem. Ideas?

Bill

[rickst29]

Great post from Bill.

The "safety", wire (always called the "grounding" wire), has important distinctions from the "current-carrying neutral" wire (sometimes badly labeled as the "grounded" wire, causing immense confusion and dangerous mistakes).

In typical wiring, BOTH are ultimately connected to a hard grounding rod at the service panel entrance. Because of this, you will usually not measure a voltage difference between them - unless a large appliance is running. But the safety "grounding" should NEVER have high Voltage or Current in correct situation - it exists only to drain erroneous and dangerous voltage from failed appliances and failed wiring.
- - -
Our first conclusion must be: The safety "grounding" wire on that plugin post is utterly wrong. If it was swapped with 120V "hot", then you would see hot skin - but no appliance would work. If an appliance or internal TM wire was failed AND the grounding wire on the post was never even connected - then "hot skin" could result from the TM wiring mistake or failed appliance. So, my advice was to fully test the TM for internal faults and mis-wirings first. They would act like a failed appliance.

But it is also clear that the "campground" service is utterly broken. "Hot Skin" is maintained, at high voltage, on the TM frame - and that wire must by definition go to a grounding earth pole, and be sufficient to drain ANY possible stray Voltage and Current which reaches the frame. If the safety grounding path doesn't work (from a bad connection, or NO connection, or being mis-connected to the "hot" lead), it must be fixed before anything is ever plugged into that 30A socket again.