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cable wall feed through with lightning protection




 
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Author Topic: cable wall feed through with lightning protection  (Read 583 times)
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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« on: November 16, 2018, 02:56:04 PM »

Here in Costa Rica we have quite a lot of lightning in big parts of the year. It really can surprise you. In addition, I tend to forget now and then to disconnect my antenna cables And I live quite high and free
So I made an antenna feed through box with protection. At the inside and the outside part, there are 600V gas arrestors that can handle quite a few thousands of Amps pulse. In between a thin piece of PTFE coax that may act like a fuse.
The box is grounded with 3 (at this moment still one) AWG8 cables to 3 ground rods which also are connected to the re-enforcement iron of the concrete of the house.
The rotor cable will be fed trough with 7 pin connectors connected with thin (fusible) wire inside the box. Both at the inside and the outside there are VDR resistors.
The 115V is fed inside the shack via a 20 Amp filter and 8000 Amp VDR protectors where the filter is grounded to the same feed through box using wide copper strip.
Lets hope that this will minimize the damage in case of bad happenings  Sad


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WBear2GCR
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« Reply #1 on: November 16, 2018, 05:18:10 PM »


Not sure what you've read on commercial lighting protection for towers and transmitter buildings??

The method used for that appears to be VERY bullet proof.
IF you could possibly implement it, and you have a high lighting strike event probability,
it would be an excellent approach.

Briefly, it's a grounded ring of heavy wire around the building, and specific connection(s) to that
from the building and electric service.

I think your idea will help with close hits, but not any like a direct or nearly direct hit.

Having said that, no I don't have such a system here. Sad

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W2PFY
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« Reply #2 on: November 16, 2018, 05:53:51 PM »

I thought about an explosive in line device for open wire that would explode when lighting hits the wire, therefore instantly separating the wire and at the same time squelching the ensuing fireball. It would only be suitable for rural settings a safe distance from one's dwelling. I think it could also be made with a high pressure cylinder that would separate upon a high current surge suitable for inter city applications. I have no patents for such a device as it's still in R & D...


Anyone have any ideas in design?   
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PA0NVD
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« Reply #3 on: November 16, 2018, 05:54:32 PM »

Thanks for the reply
Indeed I did read that article and did try to implement as good as possible. All around the house connected earth stakes and everyone connected to the iron of the concrete. The construction of the house helps a lot, underneath every inner and outer wall are nice reinforced concrete horizontal beams in the ground, all the iron is interconnected, so a network of iron underneath the house all connected to the iron in the concrete walls and the metal roof structure, a kind of cage of Faraday. Together with the ground stakes that should give a very solid ground connected with 3 AWG8 wires to 3 of those groundstakes. So I hope that that prevents a potential difference between the ground and the cables inside the house
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PA0NVD
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« Reply #4 on: November 16, 2018, 06:03:02 PM »

I thought about an explosive in line device for open wire that would explode when lighting hits the wire, therefore instantly separating the wire and at the same time squelching the ensuing fireball.

You don't need an explosive device. I think that you can reach that goal by making two separate boxes where a thin wire passes through from the input via a small hole in the separation wall to the output. At every wall (3) a gas arrester. When a heavy discharge happens, the gas arresters fire and the wire in the first  box evaporates explosive and fills the box with plasma, effectively conducting the discharge to ground via the walls of the box. I saw that happening with heavy short circuit in 416V high power lines. The second box will be free of plasma and the wire just fuses by the conducting third gas arrestor
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KL7OF
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« Reply #5 on: November 16, 2018, 06:36:08 PM »

what effect will a lightning strike have on the concrete  foundation if you are grounded to the re-bar iron within the foundation?
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W2PFY
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« Reply #6 on: November 16, 2018, 06:48:14 PM »

Quote
You don't need an explosive device. I think that you can reach that goal by making two separate boxes where a thin wire passes through from the input via a small hole in the separation wall to the output. At every wall (3) a gas arrester. When a heavy discharge happens, the gas arresters fire and the wire in the first  box evaporates explosive and fills the box with plasma, effectively conducting the discharge to ground via the walls of the box. I saw that happening with heavy short circuit in 416V high power lines. The second box will be free of plasma and the wire just fuses by the conducting third gas arrestor

Very interesting with the two box concept. Would these arrestors be the ones we see on ham radio sites or something more sustainable with higher voltage and current ratings? 
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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #7 on: November 16, 2018, 07:53:30 PM »

No, I do not use the GDT's seen at ham sites, just industrial materials. They aren't expensive
I use the littlefuse GDT's. The type SL1411A500 fires at 500V and handles 10 pulses of 10 kA So it can handle a few kW RF at 50 Ohms before firing
But there are many brands of GDT's and all very similar. All kinds of voltages and currents
Here is the Littlefuse catalog
https://m.littelfuse.com/~/media/electronics/product_catalogs/littelfuse_gdt_catalog.pdf.pdf
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KB2WIG
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« Reply #8 on: November 16, 2018, 11:19:56 PM »



"  what effect will a lightning strike have on the concrete  foundation if you are grounded to the re-bar iron within the foundation?  "

Probably very little.  Check out the following...........

https://www.ecmag.com/section/codes-standards/solid-ground-defining-and-understanding-ufer-ground

https://www.mikeholt.com/mojonewsarchive/GB-HTML/HTML/UferGroundPsi~20030930.htm

klc
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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #9 on: November 17, 2018, 09:43:04 AM »

Interesting info KLC., thanks I did read something similar and decided to use an UBER ground from the first moment they did construct the house. Was nice, I had access to all the iron to connect wires. The surface area of the concrete in the ground is large and the ground here is excellent, always wet and compact. I am not afraid of concrete damage with a strike
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KD6VXI
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« Reply #10 on: November 17, 2018, 10:49:51 AM »

Gaseous explosions in concrete from using UFER grounds was 'a thing' a few years ago.

As an electrician, I've never seen one happen.

I have heard of CEE (Concrete Encased Electrodes) exploding.  Most of those are bars driven or laid horizontal.  Concrete is used to increase their effective area, I've been instructed.

The method of explosion was hyper heated water converting to steam, causing fractures.  I can only surmise?? that a real UFER has enough contact to ground that it doesn't superheat whereas a ground bar encased in a foot to 18 inch cylinder of concrete does not.  Maybe.....  The slab has enough distributed C that it can divert the stroke to ground as well as has enough distributed C so that the stroke is distributed across a lot of concrete.  I2R says a larger conductor won't superheat as fast....

Nothing guaranteed, just ideas I bounced around while learning who Mr UFER was during that two days of concrete encased electrode instruction.

--Shane
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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #11 on: November 17, 2018, 12:19:39 PM »

underneath every wall are concrete bars of approx 2feet x 2feet square burried and poored in the soil with iron. That are many square meters in contact with a good conducting ground, so I guess I don't have to worry about explosions  Smiley
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