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Author Topic: Insulating jack pads for lightning  (Read 1143 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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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?).
------
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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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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John Roberts {JR}

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Re: Insulating jack pads for lightning
« Reply #10 on: June 05, 2018, 02:26:00 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....
When I designed my outlet tester I had to test insulation resistance at 500V I borrowed a nice hand held tester from a member of this forum.



You can impute the leakage current at 500V from the 550M resistance, while that is apparently full scale for the meter so current is less than that resistance suggests.

JR

 
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Mike Sokol

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Re: Insulating jack pads for lightning
« Reply #11 on: June 05, 2018, 02:47:41 pm »

Or maybe I need a 800kV tester??? Bwa, Ha, Ha...  :o

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Jonathan Johnson

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Re: Insulating jack pads for lightning
« Reply #12 on: June 05, 2018, 02:52:53 pm »

OK, so let's say you put your RV on insulating pads, electrically isolating it from the soil.

Lightning strikes on or near the power supply lines, energizing the hot line to a bazillion volts.

This travels to Mike's (no relation) RV. There, the surge protector shunts the excess voltage to the RV's equipment grounding conductor, which is properly connected (because Mike is a stickler for doing things right) to the campgrounds equipment grounding conductor, which is properly connected to a grounding electrode. Since the surge protector isn't rated for a bazillion volts, it blows up.

Did the insulating pads do any good?
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Mike Sokol

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Re: Insulating jack pads for lightning
« Reply #13 on: June 05, 2018, 03:07:32 pm »

OK, so let's say you put your RV on insulating pads, electrically isolating it from the soil.

Lightning strikes on or near the power supply lines, energizing the hot line to a bazillion volts.

This travels to Mike's (no relation) RV. There, the surge protector shunts the excess voltage to the RV's equipment grounding conductor, which is properly connected (because Mike is a stickler for doing things right) to the campgrounds equipment grounding conductor, which is properly connected to a grounding electrode. Since the surge protector isn't rated for a bazillion volts, it blows up.

Did the insulating pads do any good?

You're assuming transmodal voltage differentials (at least I THINK that's the proper term). But I assume there will be a common-mode voltage with all 3 conductors (Hot, Neutral and Ground) having the same voltage on them, but above earth potential. That's because lightning strikes have such a quick rise time that the inductance of the wires together will increase the series impedance at such high frequencies. In that case, will that pulse head towards earth-ground via the jacks, like the tip on a bullwhip? And if those same jacks are insulated from the earth, will that do any good at preventing the fault current from flowing though the RV's tender bits?
« Last Edit: June 05, 2018, 03:32:43 pm by Mike Sokol »
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Mike Sokol

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Re: Insulating jack pads for lightning
« Reply #14 on: June 05, 2018, 03:57:10 pm »

You're assuming trans-modal voltage differentials (at least I THINK that's the proper term).
No, I'm wrong. It's differential-mode voltage not trans-modal voltage. I'm such a do-do head...
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John Roberts {JR}

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Re: Insulating jack pads for lightning
« Reply #15 on: June 05, 2018, 04:24:44 pm »

Lightning is funny (not funny haha) which is why I suggested researching lightning damage reports as a good starting place....

I don't expect easy answers, but dropping shore power before storms might be easier when RVs start using tesla size batteries, maybe even automated with robot actuators to disconnect without going outside.

I still like my electronic lightning rods (air ionizers), and remains suspicious of shore power hook-up as the significant damage vector.

JR
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Re: Insulating jack pads for lightning
« Reply #16 on: June 05, 2018, 06:28:09 pm »

Lightning is funny (not funny haha) which is why I suggested researching lightning damage reports as a good starting place....

I don't expect easy answers, but dropping shore power before storms might be easier when RVs start using tesla size batteries, maybe even automated with robot actuators to disconnect without going outside.

I still like my electronic lightning rods (air ionizers), and remains suspicious of shore power hook-up as the significant damage vector.

JR

The Basement forum discussion about cleaning pigeon poo and working at height linked a tower climbing video.  A few minutes in they mention lightning...

https://youtu.be/hFMHjDqHL_Y?t=185
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Re: Insulating jack pads for lightning
« Reply #17 on: June 05, 2018, 06:35:12 pm »

I'd opine (from a position of no expertise) that if there was a lighting strike and this caused disruption to the local supply causing a voltage transient, I'd want everything to transient together, rather than have some stuff be a few thousands volts away from other stuff...
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Stephen Swaffer

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Re: Insulating jack pads for lightning
« Reply #18 on: June 05, 2018, 07:12:53 pm »

If the frame of the RV is properly bonded to the incoming EGC then the frame of the RV is in parallel with the EGC wiring-I think you actually want paths to earth.  If this was a home, then any and all grounding electrodes would be required to be in parallel and multiple grounding electrodes would genrally be viewed as desirable.

I think in wet conditions (high probability when lightning is a concern), rubber isolating pads would have neglible value with lightning, but they might manage to isolate the chassis enough to create a shock hazard.

My vote would be to take a chance on quite a few RVs getting wiring fried before I would place one life in jeopardy.  A lot of code grounding is focused on keeping everything at the same ground potential-and that requires connections and bonding-not isolation. Like JR, I like things that are bonded together-intentionally or not in this case.
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Re: Insulating jack pads for lightning
« Reply #19 on: June 06, 2018, 09:02:02 am »

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.
The way I figure it, once headed for the RV, that spike is getting to ground, one way or another. Isn't there a benefit to providing an easy (easier) path ?
There WILL be damage, but can it be minimized by an easy path ?
I'm no expert on this. All I know is when I see lightening, my stage get's cleared RFN. Up here in Montreal, we sure don't see the kind of shit I see on the news about some of "your" trailer parks.
Regards,
Chris.
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John Roberts {JR}

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Re: Insulating jack pads for lightning
« Reply #20 on: June 06, 2018, 12:55:06 pm »

If the frame of the RV is properly bonded to the incoming EGC then the frame of the RV is in parallel with the EGC wiring-I think you actually want paths to earth.  If this was a home, then any and all grounding electrodes would be required to be in parallel and multiple grounding electrodes would genrally be viewed as desirable.

I think in wet conditions (high probability when lightning is a concern), rubber isolating pads would have neglible value with lightning, but they might manage to isolate the chassis enough to create a shock hazard.

My vote would be to take a chance on quite a few RVs getting wiring fried before I would place one life in jeopardy.  A lot of code grounding is focused on keeping everything at the same ground potential-and that requires connections and bonding-not isolation. Like JR, I like things that are bonded together-intentionally or not in this case.
JR does not necessarily "like" unintentionally bonded together grounds, but UL sure likes their grounds. 

I have been thinking about this for decades with no obvious alternative. I did lift EGC with a relay contact in one of my prototype muso savers if I detected GFCI fault "and" above threshold EGC path current... (not UL legal).

I do like the idea of some relay or robot shore power lift device to help avoid incidental damage during local electrical storms. More robust battery storage and automatic disconnects might make this less painful for RV owners.

JR
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