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Author Topic: Insulating jack pads for lightning  (Read 1228 times)

Mike Sokol

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Insulating jack pads for lightning
« on: June 05, 2018, 08:21:33 am »

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? 
« Last Edit: June 05, 2018, 08:24:44 am by Mike Sokol »
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Mike Sokol
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Lee Douglas

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Re: Insulating jack pads for lightning
« Reply #1 on: June 05, 2018, 09:15:21 am »

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.
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John Roberts {JR}

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Re: Insulating jack pads for lightning
« Reply #2 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).

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 
 
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Mike Sokol

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Re: Insulating jack pads for lightning
« Reply #3 on: June 05, 2018, 10:51:21 am »

Being connected to a power drop may in fact increase the likelihood of damage from a nearby strike (WAG).

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... 
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Mike Sokol

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Re: Insulating jack pads for lightning
« Reply #4 on: June 05, 2018, 10:59:18 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?

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.

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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John Daniluk (JD)

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Re: Insulating jack pads for lightning
« Reply #5 on: June 05, 2018, 11:11:03 am »

So after a storm you grab the door of your above ground  rv and provide ground path.   if the storm destroys the wiring in the ground It may have some capacitance in the non working ac.  Depending on what is destroyed there may be some voltage on the ground.

I like grounded things..... 
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Chris Hindle

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Re: Insulating jack pads for lightning
« Reply #6 on: June 05, 2018, 12:37:08 pm »

So after a storm you grab the door of your above ground  rv and provide ground path.   if the storm destroys the wiring in the ground It may have some capacitance in the non working ac.  Depending on what is destroyed there may be some voltage on the ground.

I like grounded things.....

Hmmm.
Mike, what effect would a ground rod attached to the skin (and chassis)of the RV have ?
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Art Welter

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Re: Insulating jack pads for lightning
« Reply #7 on: June 05, 2018, 01:09:32 pm »

Hmmm.
Mike, what effect would a ground rod attached to the skin (and chassis)of the RV have ?
Roughly the same effect as jack pads, hence this thread discussing whether insulating them may reduce lightning effects...
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Mike Sokol

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Re: Insulating jack pads for lightning
« Reply #8 on: June 05, 2018, 01:36:10 pm »

Hmmm.
Mike, what effect would a ground rod attached to the skin (and chassis)of the RV have ?

Well, it would provide a path for the lightning current spike to earth-ground. But the question is do we really want that to happen if the spike if coming from the power outlet that the RV is plugged into? I have dozens of emails from readers having torched electrical systems in their RVs, seemingly due to a lightning hit in the power lines. So if this is a trans-modal voltage spike the MOV devices in their surge protectors should shunt that current to the EGC before it reaches into the RV's electrical system. But if it's more common-mode spike, then the MOV's in the surge protector won't actually shunt anything, and whatever voltage/current is on the wire will head through the RV and into the earth.

Again, I don't know if any of this is even relevant, but I'm trying to gather anything I can about this lightning ground effect. 
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Mike Sokol
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Mike Sokol

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Re: Insulating jack pads for lightning
« Reply #9 on: June 05, 2018, 02:13:11 pm »

So if I get into this sort of thing which is looking for leakage currents at high voltages, guess I need a hi-pot tester. Now I don't own one myself, but I have used them in the past. A quick look on FleBay shows a bunch of ones up to 5kV at reasonable prices. Sort of like this one: https://www.ebay.com/itm/GW-Instek-GPT-805-AC-Withstand-Voltage-Tester-Hipot-500VA-0-5-kV-100-mA/123167533845?hash=item1cad5b6b15

Are any of you hi-pot experts who can offer a little advice? I've seen some really big ones up to 100kV, but they're big money and I probably don't need one for this level of experimentation. Or do I?  ;) 

BTW: We really need a Bwa Ha Ha emoji....
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Mike Sokol
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