Another article from Mike Sokol about lightning safety you all might find interesting as he specifically address's lightning and fiberglass trailers.
Issue 881 • April 11, 2018
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RVing Tip of the Day
Will your RV protect you from a lightning strike?
By Mike Sokol
Since we’ll soon be in lightning season, it’s time to prepare for storm safety. Here’s a typical question about RVs and lightning I receive every year.
“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 RVs? 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 lightning 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 lightning 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 about Faraday Cages.
It also hints that the rubber tires
on a vehicle do nothing to insulate you from a lightning strike. If the lightning 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 out 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 lightning without any interior damage. I’ve actually been on a flight that was hit by lightning, 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 lightning 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 lightning 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 lightning 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 lightning 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 onboard 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 lightning storm.
I’ve also heard some people recommend lifting the leveling jacks or putting them on insulated platforms for lightning 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 campground rec center or your car and enjoy the show while the lightning zips around you. And take your digital camera to try for some time-exposure pictures of lightning strikes. I love watching lightning storms … but only from the inside of a protected place.