Beware of dangerous “Reflected Hot-Skin Condition”!

Beware of dangerous “Reflected Hot-Skin Condition”!

 

Hello, Mike,
I just happened across your YouTube video on camper hot-skin conditions and I had to relate my first experience with it. We were at a campground that had at least 8 campers plugged into a particular 30-amp electrical leg (if that is what it would be called). We had arrived earlier in the day and had no problems with any shocks. During the day as other campers arrived it had rained. In the evening as we were retiring, I had stopped outside the camper to remove my shoes when I put one hand on the camper and received a shock. Not a severe shock, but still a shock.

In the morning, I mentioned it to our next-door campers, that were people we were camping with, and they mentioned that they felt it too. So their daughter went to the office to report the concern. Of course it didn’t take long for someone to get there. They took a voltage reading from my camper to the ground and read 98 volts. I turned off the breaker to my camper as they moved down the line taking readings at each camper and turning off breakers until reaching the last camper, still reading 98 volts. As they were testing the last camper, they instructed the owner to trip the breaker for the water heater. The voltage then went to zero.

They stated that they had run across the concern before and the fault was a shorted element or control module for the heater. As long as that camper kept the water heater off, no one had a shock concern. So, needless to say, I will be purchasing a Fluke tester to check for this condition as soon as I plug in to an outlet and recheck periodically throughout the day, especially after a rain.

This may be something worth mentioning on your website or at seminars — that something such as a faulty electrical water heater can possibly cause this hot-skin condition to happen to other campers tied to the same electrical system.  A back-feed condition as it were.
 
Thank you for finding this condition and bringing it to light. It will save many lives and possible lawsuits. I will also be informing other campers that we meet about this concern and recommending they view your website and book for more information. Hopefully we can pass the word to other campers that are unaware of this hot-skin condition. Thank you again. —Robert

Hi, Robert,
Thanks for your excellent question. Interestingly, the phenomenon you describe is fairly common, and I’ve written about it a number of times. I call it a Reflected Hot-Skin Condition, since the Hot-Skin Voltage of one RV can be “reflected” to other RVs in that part of the campground. This can’t happen without a grounding failure in the campground wiring. So in your case, while the water heater element in the final RV on the campground loop provided the fault current, the voltage should never have traveled to other RVs. The reason it was able to was due to a failure in the grounding system of the campground itself. See below.

Here’s how the service panel coming into the campground should look. As you can see in the graphic below, there’s a ground rod at the power pole coming into the campground, and it’s “Bonded” (connected) to the Neutral connection from the transformer on the pole. This is what creates the actual grounding system for the campground (as well as your home wiring).

The real problem is that the wiring in your campground had a failed ground wire returning to the service panels’ neutral-ground bond in part of their electrical distribution system. That is, while all the pedestals on that campground loop had their grounds tied together, there was a failed connection back to the incoming electrical service panel. This creates what I call a Reflected Hot-Skin Condition, where a single RV with a hot-to-chassis fault will energize not only their own chassis, but all the other RVs on the same campground electrical loop. It’s simply impossible for a properly grounded RV (with a solid ground connection back to the service panel’s ground-neutral bonding point) to develop a hot-skin voltage. Just can’t happen…

So here’s what likely happened in your case. Take a look at the next diagram below where I created a broken ground wire between pedestals 1 and the rest of the campground “loop.” Since the ground wires for pedestals 2, 3 and 4 are tied together but not actually “grounded” back to the service panel’s bonding point, any small (and normal) leakage currents by a single RV will be “reflected” to every other RV plugged into these ungrounded pedestals. And simply pounding in a ground rod at your own RV really won’t “ground” your RV. It needs to have a solid connection all the way back to the service panel to be an effective ground.

What that means is that while they discovered the source of the fault current in one RV, the campground may not have corrected the failed ground continuity condition that allowed it to “reflect” the hot-skin of the original RV to others, with potentially deadly consequences. I would like to contact the campground to make sure the actual grounding fault has been corrected since they probably didn’t correct the problem. And it could become deadly in the future.  

Extra Credit

Below is a diagram detailing the standard currents and impedances in a typical RV power distribution system. This graphic is for EE’s and Electricians who need to troubleshoot grounding problems in a campground, so you RV owners won’t be tested on it (unless you really want me to).

Let’s play safe out there….

rv-safety-764Mike 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.

 

##RVT787

 

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2 thoughts on “Beware of dangerous “Reflected Hot-Skin Condition”!

  1. Mike Sokol

    That .25 ohms is the actual resistance of the interconnecting wiring. Thicker wires (lower gauge) will have a lower resistance per foot, and thus less voltage drop. Thinner wires (higher gauge) will have higher resistance per foot. This is also why a 100 ft extension cord will have twice the resistance and twice the voltage drop of a 50 ft extension cord. Advanced troubleshooting techniques for large electrical systems requires that you predict how much voltage drop will occur with a given load. So working backwards, if you know you want to draw a specific amperage from a wire, and you know the length the wire needs to run, then you can do a little arithmetic to determine just how thick the wires need to be. So the more amperage, the thicker the wire. Consider just how thick your batter jumper cables are. That’s because they need to have a really low resistance since they have to pass a few hundred amperes of current for your starter motor. While the wiring on your phone charger can have a high resistance and be very thin. It only needs to pass a fraction of an ampere current.

  2. Mel Goddard

    I am not an electrician, but rather a retired Aircraft Mechanic.
    In the “Extra Credit” schematic,; ‘Hot 2’ , Neutral and ground are leading to the hot water heater., which measures 5.5 ohms.
    But each wire up to the heater show a resistor of .25 ohms.
    What are they for?

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