How to safely test for a hot-skin condition on your RV

Dear Mike,
I’ve been following your newsletter and find it an excellent source of information. We live in the humid environment of southern Georgia and camp around the Southeast, which has been very wet, giving me some concern of the possible shock threat of “hot skin.”

Dear Norris,

I’m glad to help. Here are the basics of what a hot-skin is and how to test for it.

First of all, all RVs with AC power have a “grounded” shore power cord which needs to be plugged into a “grounded” outlet of some sort, such as a 20-amp, 30-amp or 50-amp (actually a 100-amp) source. The reason for the grounded plug (actually called an EGC for Equipment Grounding Conductor) is to keep any voltage on the chassis (and skin) of the RV very close to earth potential, typically within 2 or 3 volts. 

If you have a low-resistance connection (bond) from the chassis (and skin) of the RV to the power pedestal, which in turn has a low-resistance connection back to the incoming power panel from the power line, then there’s no way for that voltage on the RV chassis (and skin) to elevate very much (again, 2 or 3 volts) above earth potential. Realize that if you’re wet, as little as 30 or 40 volts AC on the skin of an RV constitutes a hot-skin, which can be lethal under the right circumstances. Simply put, you don’t want to put your own body in the middle between an RV with a hot-skin and the earth (or any other grounded object). 

So how to test? 

First of all there’s the gold standard test of using a digital meter and a ground rod, but that’s way too cumbersome and time consuming to do a quick test for hot-skin voltage after connecting to shore power. That’s why I developed a proximity test using a Non Contact Voltage Tester (called a NCVT or sometimes a tick-tester by electricians). 

A Non-Contact tester works by listening for the “hum” that’s in every object that’s been electrified by the power lines around us. If you’re a musician you’ve probably heard that “hum or buzz” when you pull the signal cable out of your guitar without turning off the stage amp. It’s that “hum” that an NCVT is listening for. 

First, you need to select an NCVT that will do the job. There’s a lot of confusion as to the voltage ratings on these, with a standard VoltAlert from Fluke being rated for 90 to 1,000 volts. That just means it will sense as low as 90 volts on a wire, which is really small in surface area. However, if you use it to test something as big as an RV (with hundreds of square feet of surface area), most of these Non Contact Voltage Testers will beep when they detect as low as 40 volts of hot-skin. And that’s the voltage level that can become dangerous if your hands and feet are wet. Fluke has discontinued their model that I liked and have used in many of my past videos, but I’ve found that the Southwire 40136N, which is rated for 50 to 600 volts, works very well for this application. 

Next, you want to turn on your NCVT and confirm that it’s working. I’m not a big fan of “always on” testers since I really want a light or sound when I turn it on to be sure the batteries aren’t dead. So, pushing the power button on the NCVT should make it blink or beep or light up. In this case for the Southwire tester, it beeps once and lights up with a steady GREEN light. 

You do need to grip the NCVT in your hand like a screwdriver because its circuitry is depending on your own body to provide the earth voltage reference. You don’t have to use a death grip on it, just hold it with your hand wrapped around the body of the tester. 

Next, you really need to confirm that it’s actually working by poking the tip of the NCVT in a receptacle that you know is on. You have one right in your campground pedestal, so place the tip of the NCVT in any of the hot outlets. You don’t have to worry about getting shocked because these testers have a nylon or plastic tip, which is rated for 600 to 1,000 volts. If it doesn’t beep then something is wrong and you need a new tester or maybe batteries. Note that the Southwire NCVT blinks RED and BEEPS if it finds a voltage on what you’re testing. 

Finally, if your NCVT beeps in a known-powered outlet, then simply point it at your RV and touch anything metal that’s connected to the chassis. This can be the hitch or a wheel or the metal steps. And if you have an aluminum skin on your RV then it’s also bonded to the chassis. Virtually EVERYTHING metal in your RV is tied to the chassis at the factory. Here’s a VIDEO I made showing a micro-size RV being used for the test. And you get to see “Flash” in action. 

Don’t be surprised if your NCVT beeps from up to 2 feet away from your RV. That’s a sure indication there’s around 120 volts on the RV which is a hot-skin, and you DO NOT want to touch it. If you do detect a hot-skin condition, unplug from shore power immediately and fix the problem. DO NOT test it by touching the RV with your hand. That could be the last test you ever do. 

Let’s play safe out there….

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

##RVT850