Lightning Safety

Is it safe to stay in my car, truck or tour bus during a lightning storm?

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 vehicle 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 about Faraday Cages.

tireAnd 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 vehicle, 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.

Lightning-plane-597085So let’s think about a typical tour-bus or trailer. An all metal shell like an Airstream or Prevost coach 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 tour bus or metal skin car or pickup truck should 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  shore power plug from the power pedestal during a big storm, since a lighting ground strike on hundreds of feet away could easily get directed into the underground wiring feeding all the outside outlets, and you could have a several thousand volt spike (surge) come in through your electrical panel and burn out everything inside your tour bus. 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 bus 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 or tour bus. If you have a metal caged camper with either aluminum or fiberglass skin, I would say to leave the jacks down, disconnect your shore power from the 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 sitting in a wood frame and fiberglass skin RV, or a fabric popup camper, I would head to the car with your iPod and enjoy the show while the lighting zips around you. And the absolute safest place to be in an electric storm is a large building that’s properly grounded. So if there’s a community center near you, that’s a good place to ride out the storm.

Cue Ridin’ the Storm Out –

Mike Sokol

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