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[Towertalk] Box forSPG and Lightning protectors

To: <towertalk@contesting.com>
Subject: [Towertalk] Box forSPG and Lightning protectors
From: na9d@speakeasy.net (Jon Ogden)
Date: Thu, 19 Sep 2002 15:24:38 -0500
on 9/19/02 2:23 PM, Bill Hider (N3RR) at n3rr@erols.com wrote:

> As I read some of the comments/questions about covering the lightning
> protection boxes, I'm wondering if consideration was taken into account for
> a Single Point Ground (SPG)??
> 
> If the lightning protectors are just laying around on the ground, presumably
> near the ground rod, and then coax or control cables are just run into the
> house without a SPG, what's wrong with this picture?  If that's the
> scenario, you're missing a couple layers of protection.

But if the lightning protectors are all tied into the same ground rod, isn't
that the same as the SPG?
> 
> First of all, a SPG box provides the common ground point ensuring no
> difference in potential even in the face of lightning.
> Secondly, a SPG box made of metal, rather than plastic, provides a Faraday
> shield for all wires passing through the metal SPG box.  A plastic box does
> not.
> Third, a steel box, rather than aluminum, provides a magnetic shield against
> magnetic fields (produced by lightning strikes) inducing currents into your
> cables then entering the house.
> 
Yes, but the box only shields the stuff inside the box.  What about all of
the coax that is run inside the house that is not shielded by any metal?  I
fail to see how a metal box that encloses other metal boxes is going to do
much.  

73,

Jon
NA9D

-------------------------------------
Jon Ogden
NA9D (ex: KE9NA)

Life Member: ARRL, NRA
Member:  AMSAT, DXCC

http://www.qsl.net/ke9na

"A life lived in fear is a life half lived."


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