help with "hot skin? power running through frame of camper

[hawk232]

well first off i have a confession to make... we joined the dark side

that being said, we already have an issue and this is the only forum im sort of established on so I am hoping for some help!

When I bought the camper the initial problem was that with any extension cord I was getting about 37V through the frame of the camper. Switching breakers off one at a time would slowly reduce the voltage until all of them were off. When all breakers were off, including the main, I still had about 6V running through the frame.
The next day I took two grounds off of the frame, sanded everything to bare metal, put di electric grease then re installed. After doing this, when using a grounded cord I only have 1.5V running through the frame. However, using a cord without a ground (ground broken off) I still have about 6V running through the frame. I know that a ground should always be used etc etc…. but there is never a guarantee that the ground will be functioning properly at campgrounds so I would like to get it down to below the 2V that I have heard is considered acceptable per code.
Next I pulled out the Inverter and cleaned the ground wire there. Afterwards I am at roughly 4V. I get 4V going from the frame to the earth and I can duplicate that EXACT voltage by going from the ground buss bar in the Inverter to the neutral buss bar. It seems that somehow 4-6V is being introduced into the neutral circuit. Any ideas?

For what it is worth I have a pop up that only has .9V with the same un grounded ext cord, so I know its possible and that something must be wrong with the travel trailer.

 

[fmbhappycamper]

shame on you even you feel bad about going there someone will chime in

 

[dfab]

If I understand you properly your looking for a voltage draw? If you think every thing is off look at your CO detector and other electronic devices that might pull power when off like your stereo. Are you testing AC voltage or DC

 

[Camp-N-Nuts]

As I understand you this is a "leakage current"...how are you measuring this? Frame to where? The hot wires are taken out by the breakers!
If it is a battery device...it certainly won't kill anyone!

 

[jenoble99]

It sounds like you may have an open ground or open neutral circuit. I would check continuity in both circuits, paying very close attention to the neutral circuit.

 

[hawk232]

i do believe that it is an open neutral or ground circuit. i am just not sure where to start looking for issues here!!

the voltage is AC. also, when i unplug it the problem goes away (confirming that its an AC problem)

i am check from the trailer to the earth itself.

yea, we really like the pop up but it just doesnt fit our style of camping (arrival around 9-10pm friday after work and departure sunday am by checkout). it is a bittersweet thing though since some friends of ours bought it and i get to introduce them into camping/pop ups.

 

[fmbhappycamper]

good luck,

 

[rabird]

http://www.noshockzone.org/rv-electrical-safety-part-iv-%E2%80%93-hot-skin/

 

[BigBaron]

Bupkis - who is the author of the "noshockzone"? I can't remember his nickname. He's a genius!

Is it "HiFiDave"? I think it's someone else, but I can't find him! Is it you?

 

[trav]

I'm going to guess you are using a high impedance digital meter. You are probably just measuring stray or ghost voltage. Try using an analog meter and see what you get.

 

[Retired Alex]

Bupkis - who is the author of the "noshockzone"? I can't remember his nickname. He's a genius!

Is it "HiFiDave"? I think it's someone else, but I can't find him! Is it you?

His name is Mike Sokol and his user name is jmsokol.

 

[BigBaron]

Thanks. He's a true expert on all things electrical!

Still fixing things on our new trailer... Sigh.

 

[jmsokol]

Gosh.... I go away for a 12 day cruise in the South Caribbean and all sorts of things happen. I just got back last night and still digging out from under a pile of emails, but I'll have time to answer this post in detail sometime this weekend.

In the meantime, there's really no such thing as a "ghost current" on a properly grounded appliance, be it a washing machine or an RV. All modern RVs now use a grounded Shore Power plug which should reduce any voltages caused by leakage currents to essentially zero.

The 2-3 volt max recommendation by the NEC has to do with measuring between the incoming neutral buss and the safety ground or earth ground. But in reality, your RV voltage should be around a few tenths of a volt. Essentially, your RV needs to have a very low-impedance path from its own frame to the ground/neutral/earth bonding point in the main service panel. Anything that interrupts this safety-ground path (such as chassis corrosion, loose connections in your RV, broken wires, mis-wired pedestals, mis-wired or broken extension cords or dog-bone adapters, etc...) will then allow the normal leakage currents caused by your RV appliances to "bias" the chassis of your RV to something above earth ground. That's what the industry calls an RV hot-skin. Depending on both the voltage and current capability of this "hot-skin" leakage, and if your hands/feet are wet or dry, you'll either experience a "tingle", a "big shock" or "electrocution" (death by shock induced heart failure). So ANY continuous shock or tingle from your RV is a reason for concern.

Back to digging out for now, but I'll work on a complete answer to this post in a bit.

Mike Sokol

 

[jmsokol]

I'm coming up with a simple way to test the safety-ground impedance within the trailer itself. Of course, you also need a safe shore-power connection to assure that your RV won't have a hot-skin condition.

But the first thing you need to verify is that your RV's chassis has a low-resistance connection to the ground pin on its Shore Power cord. Of course, you can use a DMM set on ohms, but since there's no real current involved it's quite possible to get false good readings where you think you have a measurement less than 1 ohms, but it won't be able to support a fault current capable of tripping a circuit breaker. Now, you can buy something called a Ground Loop Impedance Tester (GLIT) for $300 or so, but that's not in most troubleshooting budgets.

My thought process is that you could do an accurate and safe test using nothing more than a 12-volt parking light bulb in a socket with a pair of alligator clips. In practice you would clip one alligator clip to the hot terminal of your 12-volt house battery, and the other alligator clip to the ground pin on your Shore Power cord (unplugged from Shore Power, of course). If all is well with your safety ground within your RV, you should measure almost exactly the same voltage across the 12-volt light bulb as your house battery voltage. When I say close, I mean within on tenth of a volt. You could also observe the brightness (blinking) of the bulb while wiggling various wires, tapping on junction boxes, and twisting connections in your extension cords.

Since at most you would only be injecting 12 or 13 volts at perhaps 1 amperes of current into your RV ground system, there's no way for it to create dangerous voltages or currents. But certainly 1 amp of current is robust enough to test your internal safety ground for continuity to your Shore Power plug ground pin.

Now this is just part one of the test. More about part two later, but essentially you also have to confirm that the safety ground of your power pedestal is actually connected to the campsite or house service panel with a low-impedance connection. This isn't something you can take for granted, and certainly not testable with a simple 3-light outlet tester which you get for $5 at Lowes. The challenge is that testing an electrically energized outlet for a proper low-impedance ground does impose some risk to the person doing the test. So I'm thinking of a simple yet safe way for you to do this test. I'll confirm this works and let you all know how to build a cheap tester in a few days once I'm dug out of my 2-week vacation pile.

Mike Sokol

 

[jmsokol]

I'm coming up with a simple way to test the safety-ground impedance within the trailer itself.

And here it is. A simple and cheap way to test your RV's ground system for current carrying ability, which is the only way to know that your ground system is intact and can save you from harm. Note that I've included a standard 12volt 1156 bulb which draws about 2 amps and provides the current limiting, and of course you're only working with 12-volts so that's safe as well. Also note that your RV is disconnected from Shore Power while doing this test.

First, you connect this test light from the positive terminal of your RV's house battery to the ground pin on your Shore Power cord. The bulb should light up brightly. If not, then you have an open ground connection from the frame of your RV to the Shore Power cord's ground pin. That's a big NO-NO which must be corrected immediately. If the bulb lights up dimly or blinks as you move your Shore Power cord around, then you have a loose ground connection somewhere. Again, a big No-No which must be corrected. Next, if you have a steady-bright test light, you need to confirm the voltages. So using a DMM set to DC volts, measure directly across the battery terminals, which we'll assume is 12.6 volts. Then measure across the two test clips on the light bulb, and you should find very close to the same voltage, but not less than 12.5 volts in this case. If you more then 1/10 of a volt difference, then you have a corroded ground connection somewhere in your RV.

You should also repeat this test adding on any extension cords, pig-tails, or dog-bone adapters you may use onto your Shore Power cord. If the test bulb blinks or goes dim, then you have a failure in the rest of your power hookup cables. Those broken cables and adapters must be removed from service and replaced or repaired. Finally, do the test again with the test clips between the battery positive terminal and the chassis of your RV. This assures that you have a solid contact between the battery ground and the RV frame, which sometimes corrodes or is painted over during the build.

Gary Bunzer (The RV Doctor) and I will be doing a video on this test procedure soon, and you'll be able to read about it in his RV Doctor newsletter as well as my NoShockZone.org blog. But you saw it here first...

Mike Sokol
[email protected]

 

[jmsokol]

I've included a standard 120volt 1156 bulb which draws about 2 amps and provides the current limiting,

Oops... That should read a 12-volt 1156 bulb. I can't figure out how to edit on this forum...

Mike

 

[Unstable_Tripod]

I can't figure out how to edit on this forum...

It's not you. The forum only allows edits for a short time period after you post. After that time expires the post can't be edited. I intensely dislike this feature.

 

[Camp-N-Nuts]

It's not you. The forum only allows edits for a short time period after you post. After that time expires the post can't be edited. I intensely dislike this feature.

...and I can't even think about or Steve fumes! Ouch!

StormTrooper repaired it!

 

[Old_Geezer]

And here it is. A simple and cheap way to test your RV's ground system for current carrying ability, which is the only way to know that your ground system is intact and can save you from harm.

Wow is that a good, impressive article, and useful to boot. I had been following the thread but really have never considered it much. Guess what I'll be doing on a brand new camper that has not even seen the campground yet, probably this weekend?

 

[jmsokol]

FYI: Here's where you can buy a simple light fixture with a 12-volt bulb:
http://www.etrailer.com/Trailer-Lights/Optronics/MC32AB.html

and here's a set of battery clips that should wok:
http://www.walmart.com/ip/Attwood-Quick-Connect-Battery-Clips/16350979

BTW: I've heard a lot of stories about brand-new RVs with high-resistance safety grounds caused by too many layers of paint on the chassis bonding point (and the worker didn't grind down to bare metal). And I've seen brand new (imported) dog-bone and pig-tail adapters that had broken internal grounds. And, of course, once your RV is on the highway with road salt and vibration for a few years, anything's possible. This simple test should find all those conditions.

Of course, now we need a test to make sure the campground and garage outlets themselves are safe. Not to scare you all too much, but did I post my article here about RPBG (Reverse Polarity Bootleg Ground) outlets and why simple 3-light circuit testers and even $300 Ground Impedance Testers won't find them? Read about it here: http://www.rvdoctor.com/2001/07/friends-of-gary-mike.html

Mike Sokol
[email protected]