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Tuesday, January 2, 2001

Friends of Gary


As a reader of the RV Doctor Column, you know my areas of expertise are focused primarily on the living areas of the RV; the major systems, components and appliances, etc. Rarely do I venture into chassis related areas since I feel there are many others better equipped to handle some of these readers' questions. From time to time, I'll ask some of my technically-adept friends and compatriots to chime in with a response for some of those areas.

Here's a question I directed to my electrical specialist buddy, Mike Sokol:

I know an automobile or truck is a safe place to be  during a  thunderstorm with lightning, because you are basically in a metal box. How about our fiberglass RV's? Are we protected in any way from lightning or should we head for our vehicle? Walt L. (Boulder, CO)

Ah yes, the "why don't you get electrocuted when lighting hits your car" question. As many of you may already know, you are safe from lightning when inside a car with a metal roof, but soft-top convertibles are certainly NOT safe in a lighting storm. That's because as Walt hinted, in a car you are essentially inside a big metal box, and this box forms something called a Faraday Cage. This cool gadget was invented by Michael Faraday back in 1836 when he coated the inside walls of a room with metal foil and discovered that voltages would flow around the outside of the room, but never reach inside of it. See this website for more technical stuff. 

And it also hints that the rubber tires on a vehicle do nothing to insulate you from a lightning strike. If the lighting has already traveled thousands of feet from the cloud towards the earth, another 6 inches of tire insulation won't slow it down a bit. It's the metal surrounding you that forms a magnetic field that helps bend the electricity around the exterior of the box. And even though you have windows in a car, there's typically enough metal in the windshield and door columns to make a nice low-impedance electrical path around you. However, don't stick your hand outside the window in an electrical storm as you could be killed that way.

So let's think about a typical RV. An all metal shell like an Airstream is probably as safe as you can get in a lightning storm since they're shaped like a big aluminum Twinkie, and that same airplane shape allows airliners to be hit by lighting without any interior damage. I've actually been on a flight that was hit by lighting going into Chicago, and even though everything lit up very bright, the pilot said it was no big deal and indeed everything was fine. And an aluminum skin toy-hauler or race-car trailer would be just as safe in a lighting storm.

However, fiberglass-skin RVs are a different story altogether. If they're manufactured with a welded aluminum cage using fiberglass insulated panels, I'm pretty sure the Faraday Cage effect would still work. But if your RV is fiberglass over stick (wood) construction, then I would say you're not safe in a lighting storm, and you would want to wait it out in the tow vehicle.

Pop-up campers with tent fabric offer zero Faraday Cage protection, so I would never spend time inside one during a bad lighting storm. Plus if they're parked under a tree there's always the possibility of a big limb falling on your head with dire consequences. So pick your campsite carefully to avoid overhanging branches.

In any case, you'll want to disconnect your RV shore power plug from the campsite pedestal during a big storm, since a lighting ground strike on the other end of the campground could easily get directed into the underground wiring feeding all the campsites, and you could have a several thousand volt spike (surge) come in through your electrical panel and burn out everything inside your RV. But your on-board generator should be safe to run since it's also inside of your Faraday Cage. However, hooking your shore power plug into a portable generator sitting outside on the ground would be a very bad idea in a lighting storm.

I've also heard some people recommend lifting the leveling jacks or putting them on insulated platforms for lighting protection, but I'm pretty sure that would have little or no effect on any lightning ground surface charges getting into your RV. If you have a metal caged RV with either aluminum or fiberglass skin, I would say to leave the jacks down, disconnect your shore power from the campsite pedestal, and turn on your battery powered fan and interior lights for a little ventilation and illumination. Then break out the deck of cards and whatever social fluids you like, and wait for everything to blow over. If your RV has a wood frame and fiberglass skin or is a tent fabric popup, I would head to the car with your iPod and enjoy the show while the lighting zips around you. Or take your digital camera and try for some time-exposure pictures of lighting strikes. I love watching lightning storms, but only from the inside of a protected place.


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