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Insulating jack pads for lightning
Mike Sokol:
Here's something new I'm working on that I'm finally able to discuss. I've written a lot of articles about lightning safety for RVs plugged into campground wiring, and was recently asked if insulating pads under the jacks would protect the RV trailers from a lightning strike. Of course I said no, that rubber tires and an extra inch of rubber under the jack pads won't stop a lightning bolt that's already traveled a few thousand feet from the sky.
However, then I thought about it a bit and think I've been asking the wrong question. Certainly, nothing will help your RVs electrical system if your RV trailer takes a direct lightning hit. But what about the other 99.9% of the time when lightning hits the ground anywhere in the campground, and there's thousands of feet of power wire buried under the ground feeding hundreds of individual campsite power outlets (pedestals)? I'm sure that anytime lightning hits the ground anywhere NEAR a direct buried power feed that there's a big voltage spike generated in those wires. And if your RV is plugged into one of these pedestals when the spike comes through the power feed, will the spike end up traveling through your RV's electrical system, into the RV frame, and through the jack pads that are sitting on the wet ground? I have plenty of emails from my RV readers describing blown up surge protectors during a lightning storm from this scenario.
But what if the RV jacks were sitting on an inch of tire rubber, effectively insulating the entire RV from the ground. Would an electrical spike on the shore power cord of say 10kV or so not tend to pass through the RV's electrical system since the frame of the RV would have an inch of rubber "shoes"? Now I really can't say how much of this spike would be common-mode or trans-modal current, but I'm guessing a lot of it would be common-mode due to the length and proximity of all the power feed conductors.
So the question is this... Could adding 1" thick insulating rubber pads under the trailer's jack stands reduce damage to the RV's electrical system if there's a nearby lightning hit on the ground? I've been looking for any white papers or even intelligent discussions about this, but not finding much so far.
Ideas? Suggestions? Discussion?
Lee Douglas:
Zero experience in this area, but... Wouldn't the rain, that so often accompanies events like these, running off the RV, down the jacks and over the pads, provide enough of a path to ground to nullify any isolation provided by the pads? Maybe on a dry storm day, but you also have the water connection, cable/antenna and possibly phone from the site hook ups to the RV that may also provide a viable ground path.
John Roberts {JR}:
Being connected to a power drop may in fact increase the likelihood of damage from a nearby strike (WAG).
Lightning, in the wild generally begins with a low power up strike that ionizes a path that the down strike follows. Once a powerful downstroke has started, it has momentum so if the original path is disturbed it will keep coming. Lightning rods/arrestors protect by preventing the up strike.
The first question I would ask, what is their track record or history of lightning damage with RVs (and how much came in through through the external power drops?).
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While a little exotic perhaps attempt to detect a build up of local charge that usually precedes lightning strikes (another speculation), or dissipate any charge build up with air ionizer on steroids that makes air conductive enough to discharge local charges. An electronic lightning arrester :o . That could be more gee whiz and profitable than selling pointy wires.
JR
Mike Sokol:
--- Quote from: John Roberts {JR} on June 05, 2018, 10:03:12 AM ---Being connected to a power drop may in fact increase the likelihood of damage from a nearby strike (WAG).
--- End quote ---
Yes, which is why I always recommend RVers disconnect from shore power in a lightning storm. But would you really want to wade out in a torrent or rain and lightning to disconnect your big 50-amp plug? Of course stage guys do this all the time (and probably shouldn't), but the average retired RVer that's in their 70's ain't gonna do it. Plus they don't want to do without their air conditioning and other amenities during a storm.
And yes I know the insulating pads will be wet with rain, but would they provide a high-current fault path for maybe a 10kV spike on the RV chassis? BTW: I've got one of the power companies engineers who's been on the code panel about lightning calling me back to discuss typical voltage spikes due to lightning that end up on 120/240-volt power systems. Getting interesting...
Mike Sokol:
--- Quote from: Lee Douglas on June 05, 2018, 09:15:21 AM ---Wouldn't the rain, that so often accompanies events like these, running off the RV, down the jacks and over the pads, provide enough of a path to ground to nullify any isolation provided by the pads?
--- End quote ---
Perhaps some path, but I'm really worried about fault currents and I don't think a film of water will make much difference. Of course if the RV was in 2" of water with 1" pads, then the pad insulation out of the circuit.
--- Quote ---but you also have the water connection, cable/antenna and possibly phone from the site hook ups to the RV that may also provide a viable ground path.
--- End quote ---
Phone hookups at RV sites are non-existent as far as I can see, but many do have cable-tv hookups. I have pictures of CATV wiring and splitters that were smoked for a lightning strike or a open-ground line fault current flowing through them. But that's another thing to think about and put in the mix.
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