Saturday, September 23, 2023


RV Electricity – Using a Non-Contact Voltage Tester

Dear Mike,
After reading your article on RV hot-skin voltage I ordered a Southwire 40126N Non-Contact Voltage Tester, but now wonder if it’s the correct tool. According to the directions it detects voltage by putting it near a hot plug. But will it also find a hot-skin voltage by putting it next to the skin of an RV? —John Baxley

Great question John,
But first a quick review of what a hot-skin/stray voltage is. Normally, the skin and chassis of your RV is within 5 volts AC of the earth. It’s the job of the ground wire in your shore power cord and pedestal to keep it down to this safe voltage. But if the ground wire is loose or broken in your electrical connection, this voltage can rise to 30, 60 or even 120 volts. Anything over 30 volts can be dangerous to your heart, so if you detect 30 volts or more, then you should disconnect your RV immediately until the problem can be corrected.

I came up with this very simple proximity hot-skin/stray voltage test nearly 10 years ago, but the manufacturers haven’t included it in their owner’s manuals yet, which is why you didn’t read about it. But you can see it here:

I have a variable AC power supply, my VW micro-bus, and several different Non-Contact Voltage testers I always recommend for my Stray Voltage Patrol. Of course there are other brands and models that will work, but let’s keep it simple for now.

I can recommend the following Non-Contact Voltage Testers, which are available in-store at Lowe’s and Home Depot, as well as Amazon.

Fluke VoltAlert 1AC-A II rated for 90 to 1,000 volts

Klein NCVT-1 rated for 50 to 1,000 volts

Southwire 40136N rated for 50 to 600 volts

Even though all three of these testers are rated to find potentials higher than 50 or even 90 volts, they all work great at finding a stray voltage as low as 30 volts on something as large as a campground pedestal or your RV. Watch the video above to see this in action.

These same manufacturers also make dual-range testers, such as the Southwire 40126N you mentioned. And these will also work to detect a hot-skin/stray voltage as long as you leave them in high-voltage mode. If you set them in the 24-volt low range they’ll be too sensitive for this test and you can get false positive warnings. Read the directions to make sure these are set in the high-voltage range to use them for a hot-skin/stray voltage test.

If you plan to join the Stray Voltage Patrol in any capacity, then the minimum test gear you need is a Non-Contact Voltage Tester. More on this topic later, but here’s a link to what I’ve published already about joining the Stray Voltage Patrol.

Well, that’s it for now. Let’s play safe out there…


Mike Sokol is an electrical and professional sound expert with 40 years in the industry. Visit for more electrical safety tips. His excellent book RV Electrical Safety is available at For more info on Mike’s qualifications as an electrical expert, click here.



  1. Mike,

    In the video, you said you set your power supply for 30V and then demonstrated use of 3 NCVTs. All 3 alarmed, although none of the 3 advertise sensitivity below 50V. So, why are these NCVTs alarming at only 30V?


    • D’n C
      Your’re talking about my video here:
      Seems like a mistake doesn’t it. But a Non-Contact Voltage Tester that advertises a 50 volt or even 90 volt threshold will indeed alarm at 30 to 40 volts on an RV Hot-Skin/Stray-Voltage. That’s because these NCVTs are calibrated to alarm on the small surface area of an energized wire, which is not even a square inch of energized metal. However, if you energize a large object like a pedestal box (a few square feet of area) or an RV skin (a hundred square feet of area or more), the capacitive coupling will be much greater, and the NCVT will alarm at a much lower voltage. Generally that trip point is between 30 and 40 volts AC. The NCVTs I demonstrated in the video all beep as low as 30 volts AC on my tiny RV model, which has maybe 1 square ft total area. On a full size RV with a hot-skin/stray-voltage the lower alarm limit will still be around 30 volts, but the range will extend up to 1 or 2 feet. Interesting, isn’t it? Of course, for troubleshooting with an exact voltage I’ll drive a short ground rod next to the RV and measure between it and the bumper or wheel lugs of the RV. After that it begins to get complicated. But never touch the RV with your hand to see if it indeed has a hot-skin/stray-voltage after you get a NCVT alarm. That’s dangerous and possibly life threatening.

    • That’s because the 50 or 90 volt rating is for testing an energized wire, which has a very small surface area of a fraction of a square inch. When you’re testing a pedestal box for stray voltage, that’s at least a few square feet of surface area, and an RV will have a surface area of a hundred square feet or more. Basically a NCVT works by capacitively coupling between your hand holding it, and the surface that it’s sensing., So it’s listening for 60-Hz hum, and since an RV is a better antenna than a wire, the NCVT hears it much louder, and it will find a lower voltage than the rating for a small wire.

  2. Mike, I really appreciate the information on electrical safety. On your recommendation, I purchased a smart surge protector as well as a couple of NCVTs. (Gotta have one for around the stationary house, as well!) Given the fact that the surge protector Can detect a number of problems with the power source, what would be a good protocol for using them in combination? Would it be wise to start by checking the power pedestal with the NC this first? Thanks for your advice.

    • Chuck, I’m doing a full answer to a protocol in my RV Electricity newsletter, which is publishing this Sunday AM.

  3. Hi Mike,
    Not sure if I found the answer to John’s question in your reply. My RV doesn’t have aluminum siding. It has pressure layered sides. Will the non contact voltage tester pick up stray voltage from the side of my RV or will I need to bring near the metal steps?

    • Bill, your RV likely has a metal infrastructure which will act like a big antenna broadcasting 60 Hz. So I’m guessing that a NCVT will alarm anywhere near the entire body of the RV. But to know for sure I would need to do an experiment with that type of structure. What’s the brand and model of your RV? One of the things I could do the next time I’m in Elkhart is to get a few manufacturers to allow me to do a few stray voltage tests on different structure RVs. In the meantime, the best thing to do is point the NCVT close to your RV’s rear bumper, steps or hitch. Since nearly everything metal in an RV is bonded to the chassis, and the chassis is bonded to the incoming EGC/Safety-Ground, it will create a very large radiant field of 60-Hz voltage.

        • You’re welcome. I wish we could get a little more support from the RV manufacturers and dealerships to promote this hot-skin test specifically, and RV electrical safety in general. If any of you know of an RV dealership that might want to include this information in their pre-sales orientation please put me in touch with them. My direct email is

  4. Thanks for your column, it’s a wealth of information. When we arrived at our rv site this week in Old Orchsrd Beach I followed your advice and ended up discovering an open ground on the pedestal. I notified the office and they got an electrician out and all was good within an hour!

    • I’ll contact Amazon and see if they can replace the picture with the correct model. I admit it’s a bit confusing.

  5. FYI
    Your recommended Fluke VoltAlert 1AC-A II rated for 90 to 1,000 volts weblink sends the user to a Fluke VoltAlert 1AC-“E” II rated for 200 to 1,000 volts. Slightly different model.


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