By Mike Sokol
Since spring has sprung and many of us are getting our RVs ready for the season, now is a great time to review what a hot-skin/contact-voltage is, and what to do if you find one. I’ll also be posting a video about it for my RV Electricity Facebook group this weekend (if all goes well). And I will be covering this topic more in-depth during my advanced 3-hour seminars this June and September. Find out more about my basic and advanced RV Electricity seminars HERE.
What exactly is a hot-skin voltage and why is it dangerous?
Well, the term “hot-skin” seems to have originated in the RV industry exclusively, perhaps as far back as the 1960s when a few “campers” added an extension cord to run some electric lights and such. But the term “hot-skin” is almost unknown in any other industry or market.
In the power company training they call it “stray-voltage,” and that can occur on street lamps that aren’t properly grounded. And electricians and electrical engineers tend to call it “contact voltage” for anything metallic that isn’t “bonded” (what you would call “grounded”) to the power company’s service panel Ground-Neutral bonding point. Here’s a picture of a truck-mounted stray-voltage detector they use to find street light poles that are ungrounded and developed a contact voltage. But what exactly is it?
I don’t particularly like the phrase “RV hot-skin” because the actual skin of the RV has little or nothing to do with this condition. It should probably be called something like a “hot-chassis” or “chassis contact voltage,” because that’s what it actually is. But for now we’ll stick with “hot-skin” and modify it as hot-skin/stray-voltage or hot-skin/contact-voltage depending on what I’m actually describing. Again, this is the 101 primer on hot-skin/contact-voltage, so I’m not going too deep into the weeds just yet.
So what is it?
A hot-skin voltage is when the chassis (and skin) of your RV is elevated above earth potential by a dangerous amount. I consider 30 volts AC to be the lower limit of what’s dangerous since under the right conditions (wet hands and feet), that can provide enough current to cause your heart to go into fibrillation. And without immediate intervention, that means death within minutes. This is why you always want to take ANY shock, no matter how minor, as serious since the next one could be deadly. Also note that to be shocked you must be between two different voltage potentials, typically the ground (earth) at zero volts, and the door or steps of your RV, which could be anywhere from 30 to 120 volts above earth potential.
How to test for it?
I developed this test method nearly 10 years ago as a safe way for RVers to test for a hot-skin/contact-voltage without any fancy meters and probes, or using their own bodies as a tester (seriously, don’t do that). All it takes is something called a Non Contact Voltage Tester (NCVT), originally designed for electricians to check for live receptacles. But rather than electricians looking for a relatively high voltage on a small wire, I discovered that a NCVT could be used to find a low voltage on a large surface. Here’s a picture of me demonstrating this process, and you can find a video of me demonstrating it HERE.
What causes it?
Well, what causes hot-skin/contact-voltage is Part 2 of this article, which I’ll publish next week in my RV Electricity Newsletter (you are signed up for it, correct?), but the main thing to know is that if your RV is properly grounded via its ground wire in the shore power cord (not a grounding rod in the dirt), then it’s impossible for any hot-skin voltage to develop.
Yes, you can easily get 1 to 3 volts difference between the chassis of the RV and the earth, but anything more than that requires two separate things to occur. First: you need to have lost continuity in your your EGC (Equipment Grounding Conductor) which is the green/ground wire in your shore power cord. Secondly, you need to have a source of these fault currents which can occur naturally from devices such surge strips, or from something like a melted electric water heater element, or even from a pinched wire or someone putting a screw in the wall where it doesn’t belong. I wrote an extended article on this for RV Education 101 a few years ago, which you can read HERE.
What to do about it?
More on this next week, but for now the takeaway is to NEVER accept feeling a shock from your RV. If you do feel even a tingle, immediately unplug your RV from shore power and run from your generator or inverter until you can determine and fix the cause. In Part 2 next week I’ll detail more test methods and possible fault current sources.
See you then. In the meantime, let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 40+ 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.