RV Electricity – Why do hot-skin shocks occur?

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Dear Mike,
I have a Safari 40′ DP and every time I plug into shore power I feel a shock when touching any metal on the RV. For instance, if I open the under-bay door and touch the inside latch I get zapped. Can anyone tell me what would make this happen? Is it really dangerous since it’s only a “little” shock? Thanks in advance. —Shocking Blue

Dear Shocking Blue,
As designed and built from the factory, all modern RVs comply with the latest electrical codes and are inherently safe for the consumer. However, to maintain safe operation all RVs require that their shore power cord be plugged into a campground pedestal or home outlet with proper voltage and grounding. If an RV’s electrical system isn’t properly grounded, then anyone touching the body or frame of the RV while standing on the ground can receive a shock.

The vast majority of these shocks felt by RV owners are in fact caused by non-RV specific failures, such as the RV owner using an extension cord or dog-bone adapter with the ground pin broken off, or plugging into a miswired outlet in someone’s garage or basement, or even using a ground-lift adapter like you can buy in a big box store. If the electrical safety ground is interrupted, then any RV can have its surface energized with up to 120-volts AC, which may become very dangerous under the right set of conditions.

This is the so-called RV “Hot-Skin” condition often quoted on forums. The term “Hot-Skin” on an RV has been used by the industry for decades, but it’s more accurately called a “Hot-Chassis” condition since that’s where the voltage actually begins. And since the “skin” and all metal surfaces in an RV are “bonded” (connected) to the chassis they’ll all have the same voltage. Notice we didn’t say “grounded,” since that’s a term that is used too often for many things that have nothing to do with actual “earth ground.” The key to keeping an RV electrically safe is for its “skin” (and chassis) to be very close to the voltage of the earth beneath your feet. That’s because electricity needs different voltages on at least two surfaces for current to flow.

It’s the actual current flow that’s dangerous, not the voltage itself. For instance, you can watch birds landing on uninsulated 11,000-volt power lines above your street and they’re perfectly safe. This “bird-on-the power-line effect” occurs NOT because the bird isn’t grounded, but because it’s only making one point of contact on a high voltage wire. If the bird is large enough to span the gap between two different power wires, then the unfortunate raptor will complete the electrical circuit and vaporize in a puff of burnt feathers. Of course if a bird (or squirrel or even a person) touched a power wire and the grounded metal tower at the same time, there would also be a large current flow and death. But that’s really because of the voltage difference between the wire and the ground or the wire and another wire. No ground contact is actually needed.

Modern home and RV wiring is designed to keep all metal surfaces you’re likely to come in contact with at nearly the same electrical potential, within a volt or two of each other. This is accomplished by “grounding” the RV to the incoming electrical service panel’s Ground-Neutral-Earth bonding point by a continuous green “ground” wire from the pedestal back to the main service panel. This is called the EGC, or Equipment Grounding Conductor in the National Electrical Code.

Note that there can be only ONE Ground-Neutral (G-N) bonding point back at the main electrical entrance panel, and that also bonds (connects) to the ground rod. Any additional G-N bonding at pedestal sub-panels is a violation of code, as is any G-N bonding inside the RV’s circuit breaker panel or outlet wiring. So there should ALWAYS be a low resistance path (less than 1 ohm) from the chassis of the RV, through the shore power connector, extension cords, dog-bone adapter, pedestal outlet, campground distribution wiring, and finally back to the service panel connected to the overhead power line transformer.

This low-resistance connection assures that no matter what happens inside the RV’s electrical wiring, the RV’s chassis (and skin) voltage can never get more than perhaps 5 volts higher than the earth potential beneath our feet. Once the voltage between the chassis and skin of the RV gets high enough to be dangerous, then standing on damp ground and touching any metal part of the RV will allow current to flow through your body and heart, just like our camper in the graphic to the right. And that’s what you’re feeling, which certainly could be dangerous under the right conditions. But more on that later.

In the meantime, NEVER accept feeling an electric shock from your RV or any appliance plugged into an electrical outlet. That’s telling you there’s an interrupted ground, and a dangerous hot-skin voltage is possible.

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.

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Mike Sokol
Editor

That’s a question for an entire article. I’ll put it in the queue for next week.

steve roland
Guest
steve roland

Mike, I have a breaker panel just below my electric meter which is bonded to a ground rod. It feeds a standby generator switch and then runs to my main breaker panel at the house which is also bonded to a ground rod. Also have my copper plumbing piping bonded to a ground rod. You have said this is against code but why? Seems to me the more grounding the better.