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RVelectricity™ – Just Ask Mike (J.A.M.): Testing for a dangerous hot-skin voltage

Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM. Today I discuss the dangerous RV hot-skin voltage condition.

Join me for a 60-minute Zoom interview this Wednesday and Friday at 1 p.m. EST, featuring live questions from the RVtravel.com Quartzsite booth with Tony Barthel. Wednesday I’ll discuss surge protectors, and Friday I’ll discuss lithium battery upgrades. More info to come.


 


Dear Mike,
I recently pulled into a little country showground in my motorhome and plugged into a 240V pedestal. Went to check my tire valve extensions. On touching the vehicle rims I was getting a heavy tingling on my fingers. That’s never happened before or since, after connecting up to 240V. What could cause this to happen? Have alerted the showground manager just in case of faulty wiring somewhere. —Phillip

Dear Phil,
This is a condition that the RV industry calls a hot-skin, and which I’ve written about dozens of times over the last 10 years. A hot-skin voltage occurs when the skin (and chassis) of your RV is energized with over 30 volts of potential referenced to earth.

Is a hot-skin dangerous?

Yes, it certainly can be dangerous. For example, if you’re standing on the wet ground in damp shoes or flip-flops, and then touch anything metal on an RV that’s energized with 30 to 120 volts AC, there can be enough current flowing through your body to set your heart into fibrillation. That’s when your heart stops beating regularly and you could pass out quickly. Without immediate CPR and the use of an AED (Automated External Defibrillator) you could be dead in a few minutes from electrocution.


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How can I test for a hot-skin voltage?

I’ve developed and pioneered the use of Non-Contact Voltage Tester (NCVT) for discovering hot-skin voltage on an RV or appliance. You can buy these at any big box store or on Amazon. These testers look like a fat pen. They are typically used by electricians to verify if a conductor has AC voltage on it. But they also work great at finding any large energized surface, like the chassis and skin of your RV.

Which NCVT to buy?

While most of these testers are marked to find voltage in a range from 90 to 1,000 volts, I’ve discovered that even the 90-volt versions will reliably find a hot-skin on an RV as low as 40 volts. That’s because they work by capacitively coupling the 60-Hz hum into the NCVT circuitry.

However, you can also get dual-range NCVTs that will find voltage as low as 12 volts AC. I like the Southwire 40140-N for my own testing, but you can also find testers made by Fluke, Klein, Amprobe and others. Buy it from Amazon HERE.

How to use an NCVT…

Well, I’ve also done a bunch of videos of how to use one to find a hot-skin voltage, and I show this in my RVelectricity™ seminars all the time. You just push the power button on the NCVT until it beeps and poke it at an outlet you know is live to confirm it’s operating properly. Then, while holding the tester firmly in your hand, bring it close to the metal frame of your RV until it touches.

Don’t worry that you might get shocked if the tip of the NCVT touches the RV itself since these testers are all plastic and nylon, with a safety rating of up to 1,000 volts.


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Watch the video!

Here’s a video of me performing this hot-skin test on my VW Nano-Van demonstration vehicle. On a full-size RV trailer or coach this NCVT will beep from 1 to 2 feet away if there’s a hot-skin of 120 volts, and as near 1 to 2 inches away with a 40- to 50-volt hot-skin. Watch the video HERE or by clicking the picture.

Why does a hot-skin voltage happen?

Well, in order for a hot-skin voltage to occur there must be a broken ground connection between your RV and the campground or home electrical service panel. It’s possible that your own shore power cord or adapter has a broken ground connection, but I’ve found dozens of campground pedestals with a broken ground connection that needs immediate repair.

Please read this!

Here’s my tutorial on how to diagnose and repair the causes of hot-skin voltage on your RV. Read all about it HERE

Remember to never accept a shock when touching your RV or anything plugged into an electrical outlet. While you might just feel a tingle this time, it can easily develop into a dangerous amount of voltage and fault current that could become deadly.

OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.

Let’s play safe out there….

Send your questions to me at my new RVelectricity forum here.

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.

You don’t want to miss Mike’s webcasts on his YouTube channel.

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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SANDIE BOCK
4 months ago

THIS guy said he plugged into 220 volts NOT 120 volts so that would be problem #1 for me!!! HE or she is frying up the electrical of the rig!! So UNPLUG IMMEDIATELY. Can the 220 volts give the hot skin even if the 120 volts would not ?

Bill
3 months ago
Reply to  SANDIE BOCK

The standard 50 amp RV pedestal is actually 240 volts, with two “hot” lines that are out of phase. You get 240 volts between the two “hot” lines but 120 volts between either “hot” and the neutral, which is what most RVs use. Hot skin is no more likely except that there are more things to go bad.

Last edited 3 months ago by Bill
Joe
4 months ago

Mike, best practice for any voltage measuring device is live-dead-live test. In other words test a known live circuit first, test what you want to work on, and then retest on the live circuit. This now confirms that your voltage measuring device did not fail after the first live test. Sounds like nonsense however I have seen only once that the meter failed the second live test so did the meter fail? Who knows?

John Goodell
4 months ago

Hey Mike! Shouldn’t you have taken the time to correct some technical details in this question? An RV campground pedestal doesn’t deliver 240 volts! A 50 amp RV connecting plug may appear similar to a 240 volt connector, but it is dangerous and potentially expensive to let this camper believe that the plug is 240 volts!

Crowman
4 months ago
Reply to  John Goodell

I thought the same thing.

Brian
4 months ago
Reply to  John Goodell

A 50 amp RV receptacle is no different than a 50 amp range receptacle and is wired the same way, 240 volts with a ground and a neutral. The RV only uses 1 pole breakers inside so everything in the RV only sees 120 volts (under normal circumstances).
A 30 amp RV hookup is only 120 volts but a 50 amp hookup is 240 volts.

Last edited 4 months ago by Brian
Wayne C
4 months ago
Reply to  Brian

This is the correct answer

Mike Sokol
4 months ago
Reply to  John Goodell

Actually it can deliver 240 volts if the neutral opens up. And a NEMA 14-50 receptacle must be wired as 2-pole, 240-volts to be in compliance. Your RV load center will split this into two separate 120-volt feeds if everything is wired correctly. But it most definitely is a split-phase, 240/120-volt service.

Mike Sokol
4 months ago
Reply to  Mike Sokol

Please read this if you have any questions about how a 50-amp RV pedestal is wired with 240 volts. https://www.rvtravel.com/rv-electricity-power-principles-further-explained/