By Mike Sokol
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.
Dear Mike (aka J.A.M.),
I’ve been listening to your Facebook videos and have a dumb question. Would a hot skin event also happen and shock you on an all-fiberglass RV? Would the voltage still be detected by the non-contact meter through the fiberglass skin? Trying to learn more about the electric on my Born Free class C RV.
Great question. And your base assumption is correct in that fiberglass by itself is an insulator, and non-conductive. One would think that a big insulator would protect you from a hot-skin voltage, but here’s the rub. Your “all fiberglass” RV isn’t just fiberglass. It also has a steel frame, axle, wheels, bumper, tongue, door frame, door handle and perhaps a propane tank. See my graphic below left – which you can click to enlarge to full size.
Virtually EVERYTHING metal on your fiberglass RV has been bonded (connected) to the metal frame. And the metal frame has been bonded (connected) to the shore power’s ground wire (officially called the EGC or Equipment Grounding Conductor). And if you were to look inside of your fiberglass RV you might find a few 120-volt appliances, such as a microwave oven. And the microwave oven’s chassis would be bonded to the RV chassis. And so it goes…
The reason that your frame (and everything else) is bonded to the incoming ground wire is that anything plugged into a 120-volt power connection can develop a fault current to the chassis. And without a way to drain that fault current away (the EGC Ground Wire), all of those metal items (including your tow vehicle if it’s connected to the RV) will develop a hot-skin voltage. And that voltage (depending on how much current is available) can be deadly if you or a loved one touches the tow vehicle, RV bumper, door handle, wheels or anything else metal.
So if you want to test for a hot-skin voltage with a Non-Contact Voltage Tester (which is a very good idea, by the way), just point it near anything metal on your fiberglass trailer while you’re standing outside on the ground. The wheel or hitch is a great place to check. If you get a beep indicating a hot-skin/contact voltage, then immediately disconnect from shore power until you can identify what’s causing it.
BTW: Yes, I’ve written dozens of articles about how to find out what’s causing these hot-skin voltages. Just go to my last column at RVtravel.com for several articles on this topic. That’s beyond what you can get with one bite from a JAM session.
Thanks for an excellent question.
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….
Mike Sokol is an electrical and professional sound expert with 40+ 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.
##RVDT 1096; ##RVT 896