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Author Topic: Insulating jack pads for lightning  (Read 1144 times)

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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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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Mike Sokol
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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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Tim McCulloch

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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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David Buckley

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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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Chris Hindle

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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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Ya, Whatever. Just throw a '57 on it, and get off my stage.
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