Proper RV chassis grounding to prevent “hot skin” condition

Proper RV chassis grounding to prevent “hot skin” condition

 

Dear Mike,
I stumbled on noshockzone.org and it has been very informative. Thanks for the time you have put into it. I am in the process of wiring a subpanel inside an enclosed trailer and have been reading that the ground should be attached to the trailer frame. Is that the best place to attach the ground? By doing that, don’t you create a direct path to the trailer frame if the unit was hit by lightning? If I’m not understanding why that is the safest way, please correct me. 

Thanks for your help. —Marc 

Dear Marc,
It’s great that you’re trying to understand the safe way to wire things. But first I must advise you to seek help from a licensed electrician or RV technician if you’re not qualified to do this wiring yourself. Following are the basics. 

Yes, the incoming ground wire from the shore power plug needs to be connected (bonded) directly to the RV chassis, and the RV’s neutral line must always remain isolated from the chassis/ground. The reason for this is that the shore power ground wire is what creates a fault-current path that will trip a circuit breaker in the event that something shorts to the frame of the RV internally. It could be a pinched extension cord in a door, or someone driving a screw in the wall that pierces a power wire, etc. When the chassis (and skin) of the RV is bonded to the shore power ground properly, any line-to-chassis short circuit will trip the circuit breaker rapidly. And any smaller leakage currents (like from a water heater element gone bad or an aging microwave transformer) will be drained away harmlessly.

The ground wire’s secondary function is to shunt lightning strike energy AWAY from your RV’s electrical system. Without a direct path to ground, that same lightning strike will create side-flashes inside all of your RV’s electronics, destroying everything. So that’s exactly what the shore power ground wire is supposed to do: A) Create a current fault path to trip the circuit breaker in the event of a 120-volt short to the chassis, and B) Shunt lightning energy directly to earth ground so it doesn’t find alternate paths INSIDE of your RV.  

An electrically floating (non-grounded) frame on your RV is extremely dangerous since something as simple as that extension cord pinched in a door or a water heater element with a pinhole leak could electrify the entire chassis and skin of the RV without tripping a circuit breaker. When that occurs, your RV will develop a hot-skin voltage, and the next person touching the RV while standing on the ground can be electrocuted. And yes, electrocuted meaning killed by electric shock.

I must remind everyone that you should NEVER feel any kind of shock from your RV while standing on the ground and touching a metal surface such as the door handle or stairs. If you do feel a shock, then something has failed in the RV’s grounding system. It could be caused by a broken-off ground pin in an extension cord or dog-bone adapter, or maybe a failed ground-bond in the outlet you’ve plugged your shore power line into. But take this situation seriously and get it corrected immediately. In every RV electrocution I’ve ever researched, someone had been feeling a shock for days or even weeks before the event occurred. After that it only takes the right combination of wet grass or mud, and touching anything metal on the RV with a damp hand to create a potentially lethal situation.

Let’s play safe out there…. 

Mike Sokol
The No~Shock~Zone

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.

##RVT789

 

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