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Old 27-11-2020, 15:43   #16
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Re: Protecting a pelican case from lightning

Our Leopard Catamaran was struck by lightening in 2018 just north of George Town, Exumas, Bahamas. We heard the storms coming and put all handhelds in the oven.

A buddy boat saw the strike and said it was a big bolt, dead on top of the mast.

Almost everything on the boat electrical or electronic was fried. Nothing inside the oven was harmed, all handhelds, computers, Garmin InReach, phones, etc. were all spared.

YMMV but that was our experience.
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Old 27-11-2020, 17:27   #17
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Re: Protecting a pelican case from lightning

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Our Leopard Catamaran was struck by lightening in 2018 just north of George Town, Exumas, Bahamas. We heard the storms coming and put all handhelds in the oven.

A buddy boat saw the strike and said it was a big bolt, dead on top of the mast.

Almost everything on the boat electrical or electronic was fried. Nothing inside the oven was harmed, all handhelds, computers, Garmin InReach, phones, etc. were all spared.

YMMV but that was our experience.
It may be anecdotal evidence, but I bet it made you a believer.
Did you have any electronic items that were not plugged into anything and not in the oven? Did they fry too?
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Old 27-11-2020, 18:53   #18
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Re: Protecting a pelican case from lightning

Use a metal ammo can. Thx-Ace
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Old 27-11-2020, 21:30   #19
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Re: Protecting a pelican case from lightning

When you put electronic items into a metal box, is it necessary or desirable to insulate them from the metal inside surfaces of the box?
If so, what type of insulation would be recommended?
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Old 28-11-2020, 05:52   #20
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Re: Protecting a pelican case from lightning

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My understanding is that a motor vehicle will keep occupants safe from lightning as it acts as a Faraday cage, it is isolated from ground by 4 rubber tyres...
Believe it or not, tires are conductive. There is enough carbon used in tire tread compounds that the tires are reasonably conductive and do not effectively isolate the car from ground...

My electric truck has copper bars to connect batteries (138 volts) working on them one day I got tired of hitting/touching them and thought I would get some heater hose from the auto part to insulate them, boy was I wrong, touched the hoses and got a shock, WTF, took a volt meter and checked voltage touching the rubber hoses, there was NO voltage drop.... rubber used in in cars is conductive... ie: carbon
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Old 28-11-2020, 06:41   #21
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Re: Protecting a pelican case from lightning

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Originally Posted by Ivansgarage View Post
Believe it or not, tires are conductive. There is enough carbon used in tire tread compounds that the tires are reasonably conductive and do not effectively isolate the car from ground...

My electric truck has copper bars to connect batteries (138 volts) working on them one day I got tired of hitting/touching them and thought I would get some heater hose from the auto part to insulate them, boy was I wrong, touched the hoses and got a shock, WTF, took a volt meter and checked voltage touching the rubber hoses, there was NO voltage drop.... rubber used in in cars is conductive... ie: carbon
That seemed like worth testing, so I did!

It turns out that the measurement using a Fluke multimeter between the steel rim and tyre tread of my pickup is 30 M.ohm, so it is a conductor albeit a poor one.

Tomorrow I will retest with a 500v insulation tester which will provide a much more accurate result.

Glad I tested this before taking anyone a bet, 'cause I would have lost!
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Old 28-11-2020, 07:56   #22
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Re: Protecting a pelican case from lightning

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That seemed like worth testing, so I did! ...
... Tomorrow I will retest ..
You might soak the tire with water, to simulate typical rain conditions, that often accompany lightning.
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Old 28-11-2020, 08:23   #23
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Re: Protecting a pelican case from lightning

A few points. I used to work with high voltage pulsed systems.

1: not all black plastic and rubber is conductive but an awful lot is. I was taught to assume everything black conducts.

2: I’ve built a few faraday cages. These were not theoretical cages, but cages that held in (which is the same as holding out) some nasty nasty electrical pulses.
Openings of even a few inches in length were nearly as good as an open door. We would destroy phones from 20 feet if not well done.
I
Expanded copper screen works great. Woven mesh is ok. Til it oxidizes.
Copper foil is great, but a pain to work with.
1/4” steel works too, as long as it’s welded and fastened and gasketed. The gasket is used on a door to provide continuous connections.

Faraday cages are great, but they take some care in construction.
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Old 28-11-2020, 09:34   #24
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Re: Protecting a pelican case from lightning

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...
Openings of even a few inches in length were nearly as good as an open door. We would destroy phones from 20 feet if not well done.
Expanded copper screen works great. Woven mesh is ok. Til it oxidizes.
Faraday cages are great, but they take some care in construction.
So, what grid size screen or mesh do you recommend, for lightning shielding?

The rule of thumb for a Faraday cage, is that the openings (screen, mesh, etc) should be no larger than 1/10th of the wavelength you’re trying to prevent transmission (block).

The frequency is related to wavelength by the following equation:
f = c ÷ γ
v = c ÷ f
Where f = frequency in Hz, c is light velocity, and γ represents wavelength in meters.

Lightning is known to emit significant electromagnetic energy in the radio-frequency range from below 1 Hz to near 300 MHz, with a peak in the frequency spectrum near 5 to 10 kHz for lightning at distances beyond 50 km or so. Further, electromagnetic radiation from lightning is detectable at even higher frequencies, for example, in the microwave (300 MHz to 300 GHz) and, obviously, in visible light (roughly 1014 to 1015 Hz). At frequencies higher than that of the spectrum peak, the spectral amplitude varies roughly inversely proportional to the frequency up to 10 MHz or so and inversely proportional to the square root of frequency from about 10 MHz to 10 GHz. Also, lightning is known to produce X-rays (up to 1020 Hz or more), although at ground level they are usually not detectable beyond a kilometre or so from the source.

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Old 28-11-2020, 10:06   #25
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Re: Protecting a pelican case from lightning

Sounds like a job for a cake tin.
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Old 28-11-2020, 10:17   #26
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Re: Protecting a pelican case from lightning

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A faraday cage is is a uniformly conductive shell. Not important for it to be made from high permeability material (magnetizable) but it is important to have no long non-conductive openings. External grounding of the cage is irrelevant.

It operates by causing a zero electric field inside itself when the cage is subjected to an electric field (such as nearby lightning strike), protecting the contents from conductive currents or high electric field damage.
Yes, I have a degree in this stuff.
I believe you have made a good point. There seems to be a confusion between a Faraday's cage and providing the easiest path to ground for a direct strike.
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Old 28-11-2020, 11:56   #27
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Protecting a pelican case from lightning

I’d wrap hand held equipment in a layer of fine expanded copper, Then stick it in the oven. Because I have some.
And it will depend on the strength of the strike.

We used copper window screen, so about ten or more to the inch for our stuff we wanted to see.

Onlinemetals has thin copper foil .0007” for not too much. That would be pretty darn good. It is alloy 110. It will eventually work harden but you could easily cover a pelican case with it. As long as the case opening has adequate pressure to ensure contact all around it should be ok. And maybe if you want to go wild use some thin tinned copper braid as a gasket to help ensure contact.

I think that is probably overkill.

Again, this is all fuzzy because the proximity of the strike and the specific nature of the path it takes will affect the intensity and spectrum of the fields.

My dad got a direct masthead hit. He lost both alternators, most electronics. And his windlass, which he discovered after dropping the hook to take stock. He is not sure if his extreme muscle aches were from the bolt flinging him back from the wheel or from pulling up 150’ of 3/8” chain and a 60 pound anchor by hand.

I think that is more in the category of things I’m concerned about than the electronics.

And, I am not a lightning expert. I used to be pretty good at pulsed power stuff. A few careers ago. They are related but not identical fields.
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Old 28-11-2020, 12:27   #28
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Re: Protecting a pelican case from lightning

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Use a metal ammo can. Thx-Ace

I think I would go this route too, and skip the pelican case. Ammo boxes are sturdy, and just about waterproof. For extra waterproof, stick the GPS, phones and other devices in a ziplock bag, then into the ammo box.
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Old 30-11-2020, 10:00   #29
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Re: Protecting a pelican case from lightning

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Originally Posted by markcouz View Post
My understanding is that a motor vehicle will keep occupants safe from lightning as it acts as a Faraday cage, it is isolated from ground by 4 rubber tyres...

Have a look (online) what a "rubber" tyre really contains...
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Old 30-11-2020, 10:30   #30
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Re: Protecting a pelican case from lightning

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Originally Posted by hzcruiser View Post
Have a look (online) what a "rubber" tyre really contains...
That and the few inches of possibly wet tires and the lightning voltage, I'd have to believe what saved my ass was a discharge to ground.
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