Things that don’t cause a hot-skin voltage…

Does reverse polarity, flipped battery cables, or a missing ground rod cause you to feel a shock?

From the Forest River Forums

Originally Posted by DirtSquirt

I replaced the valve on my black water flush out system today and noticed that when I touched any metal part of the frame of my trailer, I could feel an electrical current running through it! Not enough to really shock me, but certainly enough to cause some discomfort. It doesn’t matter where on the frame I touch, either – it feels the same. What is going on? I have a 2010 Rockwood Roo 23 RS.    

Originally Posted by jmsokol

This is Mike Sokol from the No~Shock~Zone, and I just received a private message from the forum moderator that I was needed here, sort of like the Batman Signal, I guess….

OK, let’s get to the bottom of this quickly, since this is a simple thing. But first, let me detail what it is NOT!

It’s NOT caused by reversed or flipped battery cables.

And you certainly don’t want to be swapping battery cables at any time since that really DOES reverse polarity and could easily destroy electronics such as your inverters, televisions, stereo systems, etc. That’s because a battery has a positive and a negative pole, so reversing the cables actually reverses the polarity, and electronics are VERY sensitive to polarity reversal and can be destroyed by it in a few milliseconds (a millisecond is 1/1000 of a second).

It’s NOT caused by reversed AC polarity

Unless something else is miswired at the same time, reversed AC polarity won’t cause a hot-skin voltage..

Reverse AC polarity is defined as the Hot and Neutral wires being swapped or “reversed” in the extension cord or outlet. But the White Neutral wire is supposed to be isolated from the frame/skin of your RV according to the NEC (National Electrical Code) and RVIA (Recreation Vehicle Industry Association) build codes. If you’ve accidentally bonded (connected) the Neutral and Chassis Ground together, then it’s possible that a Reversed Polarity Outlet could energize the RV chassis/skin, but if the ground wire is intact it should trip the circuit breaker immediately.

A missing EGC ground wire will allow a hot-skin voltage

It’s definitely some sort of compromised EGC (Equipment Grounding Conductor) more commonly called a safety ground, or simply “ground” by most consumers. This “ground” is supposed to drain away any small ground fault currents and trip a circuit breaker for any large ground fault currents.

By definition, a ground fault current is any sort of leakage between the incoming hot wires and the chassis of an appliance or your RV itself. There will ALWAYS be some ground fault current available in ANYTHING plugged into a power outlet, but it’s normally very small, typically less than 1 mA (1 milliamp or 1/1000 of an ampere). Most of the time there will be a balancing act between the hot and neutral leakage impedance with the open ground hot-skin voltage biasing to around 1/2 of the line voltage.

So if your EGC (ground) wire is compromised without anything else being wrong in your RV, you’ll often measure 40 to 80 volts between the RV frame and a screwdriver stuck in the earth. While this sort of low-current ground fault may not be immediately deadly, you still need to take it seriously since it can turn into a high current ground fault in a heartbeat, and there will be nothing to stop it from killing you or a loved one.

OK, now let’s consider what can compromise your RV’s grounding system. There needs to be a solid connection between the frame/chassis of your RV all the way back to the electrical service panel feeding your home or the campground. So everywhere there’s a connection, it’s possible for a failure to occur. That means that it could be caused by a broken or loose or corroded connection in your shore power cable, extension cord, dog-bone adapter, pedestal outlet, or even the AC power feeding the pedestal or outlet itself. I’ve seen loose grounding screws inside of the RV’s circuit breaker box cause this, and even a broken ground screw on the back of the RV’s shore power jack on the side of the vehicle. To be code compliant, this EGC (ground) needs to have less than 1 ohm impedance back to the service panel’s G-N-E bonding point.

It’s not caused by a missing ground rod

Also, a ground rod connected to the frame of your RV does NOT “ground” your RV.

Lot’s of reasons for this, but an earthed ground rod can often measure up to 100 ohms to the earth; so while it might drain away a low-current ground fault, it certainly CAN’T drain away a high-current ground fault. That can be caused by a screw being driven though a wire in the wall, or insulation worn through by rubbing on the frame, or even a failed transformer in your microwave oven. As a side note, jacks on the ground do nothing to “ground” your RV, so don’t get me started on that subject.

A Reverse Polarity Bootleg Ground is extremely dangerous

Finally, there’s one really dangerous outlet miswiring condition I sometimes find in old garages and church outlets.

I call it an RPBG (Reverse Polarity Bootleg Ground) and it can’t be detected by any standard tests including 3-outlet testers or even metering between H-N, H-G and N-G. You must have an external reference to earth to find it.

Next week I’ll post my article “Failures in Outlet Testing Exposed” that published in Electrical Maintenance (EC&M) Magazine and my video on how you can use a NCVT (Non Contact Voltage Tester) to easily find a hot-skin condition.

So, please take any felt shocks as a sign that something is seriously wrong with your RV’s ground system, which could be anywhere from the outlet itself, dog-bone adapter, extension cord, shore power cord, or even the ground bonding point inside your RV itself. I get all the police and inspector reports whenever someone is electrocuted (killed) by an RV or guitar on stage, and most every instance was preceded by someone noticing they were feeling a shock for a few days or even weeks. Modern code requires that RVs and appliances are designed so that you NEVER feel a shock. If you do, then the grounding system has failed. It’s as simple as that.

Read my book, and don’t post dangerous electrical info

I have seen hundreds of incorrect and dangerous posts on dozens of forums about all aspects of RV electrical grounding and the causes of hot-skin voltage. And many of these erroneous posts were made by RV technicians and self proclaimed “experts”.

But this is really Electrical Grounding and Bonding 101 that I’ve known about for nearly 50 years.So please study-up before you post about RV hot-skin voltage causes and conditions.

Also, at the risk of self-promoting, I think that all of you who do RV wiring need to read my book “RV Electrical Safety.” This is a must-read before doing any electrical work on your RV, and will give you enough information to discuss electrical problems with a trained technician or licensed electrician. You can purchase it from Amazon in paperback or Kindle format HERE.

Let’s play safe out there…. Mike