RVelectricity: Testing for a dangerous hot-skin voltage

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By Mike Sokol

Dear Mike,
I’ve really enjoyed reading your electricity articles on RVTravel.com and noshockzone.org. Very informational and I love the geeky details!

I’ve recently bought my first RV (used). While parked at my house on an extension cord (GFCI-protected 20-amp garage circuit), I was crawling around underneath and felt the hair on my neck stand on end while close to the axle. It was noticeable, but I wrote it off as static electricity from my wife running a carpet shampooer inside the unit. A few days later I stumbled upon your hot skin article and it spooked me. Since then I’ve done the following tests:

  • Non-contact voltage tester beeps anywhere within 6” of the RV when plugged into garage outlet.
  • Garage outlet checks out okay with a yellow GFCI lighted receptacle tester. Extension cord and dog-bone adapter show continuity with a voltmeter including no cross-wire continuity.
  • While plugged into garage outlet, all outlets inside the RV show no ground using the yellow lighted receptacle tester (one outlet on the outside isn’t functioning at all).
  • Finally, tonight I was able to confirm with a voltmeter, up to 42 volts coming off the frame when grounded to a water main shut off in my lawn.

I have been in contact with both of my local RV dealers and both are scheduling service in July. I’ll try calling again tomorrow to see if they can work me in, now that I’ve confirmed the hot skin, but in the mean time I’m wondering if there’s other trouble shooting I can do?

Your articles talk about the power source being the issue most of the time, but it seems the outlet I’m using is sound. Any direction or additional article you can offer is appreciated. Regards, Matt, Casper, WY

Dear Matt,
You have a right to be concerned because anytime you feel a shock from an RV that means your shore power ground has become compromised. So disconnect from shore power until you can find and fix it. Even GFCIs can fail to trip, so you don’t want to be part of that experiment.

To find the problem you first need to measure the continuity of the ground pin of your shore power cord where it connects to the chassis of the RV. It should be as close to 0 ohms as your meter can measure.

You do this by setting your digital meter to the lowest ohms scale it will read (mine goes down to 200 ohms) or continuity/diode. After setting to the proper scale, touch the meter leads together. It should be very close to zero ohms (typically less than 1 ohm depending on meter calibration). Now touch one of the probes to a non-painted surface of your chassis (a lug nut on a wheel can be a good spot), and the ground pin on your shore power cord (unplugged from power, of course). It should measure less than 1 ohm and as close to zero ohms as your meter will measure. If it reads anything between 2 ohms to hundreds or thousands of ohms, then you have a bad grounding connection inside of your RV causing the problem.

It’s also possible for a loose or corroded ground connection in your house wiring to allow a 3-light outlet tester to show that the ground is okay without any load on it, but once you plug your RV into the outlet there may be sufficient ground fault leakage from the RV to create the hot-skin voltage you measured.

I would test the house electrical outlet with the 3-light tester while the RV is plugged into it. If it then shows an open ground condition the problem is in your house wiring. If the house outlet shows that the ground is okay while the RV is plugged into it, then the problem is in your RV wiring. Divide and conquer.

However, I suspect your problem could by a poor ground wire connection inside of your RV’s power center that’s supposed to bond the shore power ground to the RV chassis ground. The wiring in your RV should be inspected every year for loose connections, but hardly anyone does this simple maintenance. But you really should use a proper torque limiting screwdriver so you don’t strip any screws or break any terminals. Read all about it HERE.

So go ahead and test everything and let me know what you find out. You don’t want this hot-skin voltage to continue as it’s very dangerous and could injure or kill someone.

Let’s play safe out there….

 

 

Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.

For information on how to support RVelectricity and No~Shock~Zone articles, seminars and videos, please click the I Like Mike Campaign.

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