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Old 08-07-2015, 08:10 AM   #1
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1979 31' Excella 500
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Electrified Skin Alarm?

I'm in the process of renovating our '79 Excella 500 and ran into a situation where a electrical component I was using somehow caused a short in the 120v system that electrified the skin of the camper (still trying to help the manufacturer figure out what the problem with their product is). It freaked me out to know that such a thing could happen, independent of good or bad wiring in the camper.

What I'd like to know is if anyone can think of a way to rig-up an electrified skin alarm. Maybe such a thing already exists as a consumer product?

In theory, I think it would involve using something to detect voltage on the skin of the camper, then once it reaches a certain level to trigger a device (like a light or an audible alarm). In practice, I'm not sure what components would enable me to do this. I think I would need something touching the earth ground all the time in order to read the voltage on the skin, so I'm not sure how I'd accomplish (maybe dangling a wire beneath the trailer?).

Anyway, I'd really like to rig-up some system to warn me of this condition in the future. Any advice would be appreciated. Thank you!
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Old 08-07-2015, 08:23 AM   #2
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There are testing devices available which indicate improper wiring such as open neutral, open ground, and reverse polarity. You simply plug the device in to an outlet in the coach. You can also use this device to test the wiring at the receptacle prior to plugging in at home or campground.
A properly wired and grounded coach would not have hot skin as the breaker would trip.
As noted in many post here, the neutral in the coach wiring should NOT be bonded.


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Old 08-07-2015, 08:52 AM   #3
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Non-contact AC voltage detectors are readily available for $12-$20. I bought a couple for our WBCCI unit. Some have audio alarms as well as lights. They are internal battery powered, so you can not leave them on all the time. Airstreams used to come equipped with reverse polarity detectors. Defects in appliances can also be at fault. Always ground your trailer to be safe. GFI's and plug-in three light testers are not enough.
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Old 08-07-2015, 10:59 AM   #4
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Originally Posted by dwightdi View Post
Non-contact AC voltage detectors are readily available for $12-$20. I bought a couple for our WBCCI unit. Some have audio alarms as well as lights. They are internal battery powered, so you can not leave them on all the time. Airstreams used to come equipped with reverse polarity detectors. Defects in appliances can also be at fault. Always ground your trailer to be safe. GFI's and plug-in three light testers are not enough.
Thanks for the recommendation dwightdi. I actually looked into this and in order for them to work, they detect "ground" by the user standing on the ground and wrapping their hand around the unit. In my case, I want something more "hands off", something that will just sit in a corner somewhere and starting blinking or beeping when there's a problem.

Quote:
Originally Posted by TG Twinkie View Post
There are testing devices available which indicate improper wiring such as open neutral, open ground, and reverse polarity. You simply plug the device in to an outlet in the coach. You can also use this device to test the wiring at the receptacle prior to plugging in at home or campground.
A properly wired and grounded coach would not have hot skin as the breaker would trip.
As noted in many post here, the neutral in the coach wiring should NOT be bonded.
Thanks for the input TG Twinkie. In my case, all the trailer wiring and household wiring was/is correct (no reverse polarity, open ground, or bonded neutral and ground) but it was a faulty component (in my case a surge protector) that was causing the problem. So I don't know if devices that detect improper wiring would work here. Nonethess, I'll give it a try. Thanks for the tip.
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Old 08-09-2015, 09:05 AM   #5
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What you are encountering is a rare equipment failure, but very real in its implications. (I have had the stuffings scared out of me by touching the frame of a trailer and making your same discovery.) There is only one definitive solution and that is to have the skin of the trailer thoroughly grounded. In fact, from the factory it should be grounded, but there are a lot of assumptions involved. If your '79 is a rebuild, the grounding must have been disconnected and not replaced. A hefty copper wire bolted and lock-washered to the skin, and at the other end to any ground wire in the 115 volt system should get the job done, but you must check the ground circuit to ensure it is actually attached! I have encountered unattached ground wires in our house as well as in various RVs I have owned over the years.

If you really, really want to be sure of skin grounding, there are two things you can do. The first is to get behind the shore power receptacle and run a ground wire from shore-ground to the skin, and the other is to attach a heavy-duty copper wire to the skin near the tongue and to a steel grounding rod, which you would then hammer into the ground at each set-up prior to attaching shore power.

Believe it or not, that grounding-rod method was a mandated procedure when I operated out of an electronics intelligence van in the Army. The generators we used were also supposed to be stake-grounded, but just in case someone failed to do so and a short to ground developed, an extra route for the current to flow other than through someone's body was a life saver!
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Old 08-09-2015, 10:25 AM   #6
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and the other is to attach a heavy-duty copper wire to the skin near the tongue and to a steel grounding rod, which you would then hammer into the ground at each set-up prior to attaching shore power.
A heavy-duty jumper cable works for this and is easy to attach each time you make camp, and detach every time you break camp.

Rather than driving a steel stake into the ground— which might be difficult to drive, and even more difficult to remove when you're done— if you are at a campground that provides a water hookup, connect the ground wire to the steel water pipe, close to the soil. A few hundred feet of buried steel water pipe makes an excellent ground rod. Of course if the campground is plumbed with PVC or doesn't provide a water hookup at all you're back to driving your own ground rod…

For those times when you've got to drive your own ground rod, an old crowbar or tire iron does the trick nicely, and the curved end is shaped to make it easier to remove since it forms a handle you can grab.
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Old 08-09-2015, 02:26 PM   #7
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Electrified Skin Alarm?

This is worth a million bucks!
Costs $3 at walmart or wherever....
Plug into your power source prior to plugging on your Airstream!
Folks don't realize that when the hot and neutral are reversed, the shell is guaranteed hot. If you have wet feet and touch the shell.... Poof, you're dead! There is no loophole in this, you've touched an energized shell and you are in the path to ground!
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Old 08-09-2015, 03:35 PM   #8
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Voltage can only be detected between two things, i.e. the skin and ground, but not the skin and air, at least not at the 60 Hz line frequency. In the case of the handheld unit your body is providing the (capacitive, high resistance) connection to ground. The resistance is kept high in the design of the unit to minimize the potential for shock.

Leakage from hot to ground in any three wire component in the trailer can result in a hot skin. This can occur from faulty components in almost anything, but a converter is a prime candidate.

A connection between neutral and ground in your distribution panel, which is required by code to be connected to earth ground at your power entrance point (power meter), is no guarantee that there will not be potential (voltage) between your trailer skin and ground several tens or hundreds of feet away. Many things can cause a difference in potential at a point some distance away. The only way to be sure there is no voltage between the trailer skin and ground at the trailer is to drive a ground rod at the trailer.

Something else to check: Neutral (AC White wire) should not be connected to ground (AC green wire) in your trailer. They should only be connected at the power distribution panel.

A connection between neutral and ground in your distribution panel which is required by code to be connected to earth ground at your power entrance point (power meter) is no guarantee that there will not be potential (voltage) between your trailer skin and ground several tens or hundreds of feet away. The only way to be sure is to drive a ground rod at the trailer.
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