Lightning Safety

May 27th, 2013 | By | Category: RV Safety
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RV Lightning Safety

Is it safe to stay in my RV during a lightning storm?

This series of articles is provided as a helpful educational assist in your RV travels, and is not intended to have you circumvent an electrician. The author and the HOW-TO Sound Workshops will not be held liable or responsible for any injury resulting from reader error or misuse of the information contained in these articles. If you feel you have a dangerous electrical condition in your RV or at a campground, make sure to contact a qualified, licensed electrician.

Copyright Mike Sokol 2011 – All Rights Reserved

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)

no_shock_zone_newsAh 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 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 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.

Airplane_LightningSo 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.

RV_PedestalIn 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.

Mike Sokol

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13 Comments to “Lightning Safety”

  1. Ray Burr says:

    Good article Mike. Our fifth wheel is aluminum frame and steel chassis, I do un-plug, amazing how many others in the campground don’t. heh Then the storm hits , I feel pretty safe. Thing I’m most afraid of is hail, if it gets big enough it can write off a RV. Oh and I also wind down my TV Antenna, not sure if that helps but I figure the less metal objects sticking up the better.

    • Mike Sokol says:

      I do think that winding down the antenna is a good idea. The currents induced by even a near lightning strike can be on the order of thousands of amperes. And the Faraday cage formed by the aluminum walls of your RV won’t shunt the currents away from the antenna since it’s outside the walls of the enclosure. So the antenna could route a big pulse of current directly into your television electronics, probably the most sensitive appliance in your RV. I’ll make a note to update this article to including winding down any antennas prior to a lighting storm.

    • Mike Sokol says:

      Ray,

      Here’s my latest article about Reverse Polarity Bootleg Ground Outlets published in EC&M Magazine. Please feel free to republish the link on your own website. See http://ecmweb.com/contractor/failures-outlet-testing-exposed

      • Ray says:

        Thanks, looks like a very thorough article, good job! Just in the middle of a website revamp but will read through it and link it up on my site when I get some time. I want to update the PI surge protector post and add your links as a cautionary note. Cheers Ray

  2. Greg Hill says:

    Mike, you’re spot-on about the (non-)value of the few inches of rubber tire between the vehicle and the ground. Ever seen the aftermath of a crane strike on a high-voltage power line? Here’s one where a crane hit a 130kV distribution line: http://www.ksl.com/?nid=148&sid=25835284 . A lightning strike is likely to put this “little incident” to shame. That crane has much taller tire sidewalls than any normal passenger vehicle, yet the arc from the steel wheel to the ground made plenty of heat to melt the tire sidewall and allow a blow-out. Lightning won’t have any trouble jumping the gap from the car body to ground below. As you stated, the same thing applies with leveling jacks etc just as it did with the wood discs under each outrigger on this crane: useful to spread the weight over a larger area of soil, but totally irrelevant in a high-voltage insulation/arc-prevention sense.

    The only thing I’d disagree with is the idea about avoiding use of a portable generator during a storm: I don’t see it making any material difference in whether the lightning will strike the RV nor in the damage such a strike could cause. As already discussed, with the landing gear/leveling jacks already on the ground and the tires insignificantly insulated from it, I don’t expect that the generator sitting nearby will significantly affect the grounding of the trailer body. At lightning-scale voltages, it’d be the same as having the shore power cord laying on the ground unplugged beside a pedestal and not much different from having that cord fully stowed.

    • Mike Sokol says:

      I’m not saying that the generator on the ground will increase any danger inside your RV due to “grounding” on the dirt. Rather the generator itself will be at risk of being damaged by the lighting strike, and could act to antenna to funnel a big spike of electricity into your RV’s internal electronics and appliances. So I don’t think plugging into a generator or shore power during a storm increases the human risk. But it certainly increases the risk of electrical damage.

  3. Jo says:

    I have yet to buy an RV, and now I know one of my criteria that I did not know I had, until reading this article.

    I have known folks who have had lightening strike their homes, right thru the roof it went, causing substantial damage. Would a metal roof protect a sticks and bricks from lightening damage also, or not due to the wood framing?

    Lightening has always scared me, I now know more about keeping my family safe!

    Thanks for writing such a great article!

    • Mike Sokol says:

      I’m pretty sure that a metal roof on a building wound have to be grounded. If that’s the case, then it would form a sort of Faraday umbrella over the contents of the house. I’ll ask one of my construction buddies if that’s the case. Excellent question…

      Mike Sokol

  4. John says:

    Has anyone thought of lightning protection for a trailer? 10″ aluminum air terminals connected via braided aluminium wire every ten feet with grounding plates on opposite corners.

  5. Jenn Grover says:

    Great article, Mike. What about “alumifiber”, which is aluminum sheeting on the exterior backed by fiberglass? The T@b teardrop trailers are alumifiber on the outside. The bottom is not alumifiber, it is another composite material (not wood.)

    I have seen some refer to it as a Faraday Cage, but I didn’t know if the thin aluminum sheeting was sufficient and if the lack of aluminum on the bottom of the trailer.

    • Mike Sokol says:

      That’s hard to know for sure without testing. I’m guessing it won’t have sufficient mass to avoid localized heating and meltdown. So there’s the possibility of a lightning strike punch through. Wish I had some test material and a really big Tesla Coil. That’s would be an interesting experiment.

  6. Gwen says:

    Mike,

    First of all thank you for your many articles and you tube videos covering this very important subject. One thing I have not been able to find any information on is how safe a propane tank is on your RV or Camper if the RV/Camper is struck by lightning. I am looking for a camper or tear drop trailer with aluminum skin that is safe to sleep in during a lightning storm. My concern is the exterior propane tanks that sit on the trailer hitch, as well as a propane tank inside a truck camper.

    A book I recomend to anyone who wants to better understand how lightning works and how to limit the odds of getting hit by lightning when outdoors, this is the best book I have been able to find. It is published by Mountaineers Books:
    http://www.mountaineersbooks.org/Lightning-Strikes-P296.aspx

    The following book I do not have, but it is my understanding that it is highly regarded, although written for someone with a scientific background:
    http://ebooks.cambridge.org/ebook.jsf?bid=CBO9780511585890

    Regarding Jenn’s question Chapter 3 may be relevent. Based on the formula I figured (rough estimate) an ideal thickness of aluminum skin would be around 1/4 inch. The thing is aluminum skin on most campers is much thinner, not to mention sheet metal on a car, so I would welcome your take on this formula, and or advantages if any of having a thicker metal skin.

    • Mike Sokol says:

      I’m not sure that it needs to be 1/4″ thick to be effective. Airplanes have aluminum skins much thinner than that and they get hit by lighting all the time. I think the key to keeping propane tanks safe in a storm is to make sure they’re properly bonded to the frame of the RV. That means secure metal straps without corrosion. But I’ll think on this a bit more and see if I can come up with any additional info. I do know a retired Boeing engineer who worked on aircraft skin repairs, so maybe I can get a little more info on skin thickness there.

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