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Re: [TowerTalk] Lightnig Arrestors at tower base or house entrance?

To: Alfred Frugoli <>
Subject: Re: [TowerTalk] Lightnig Arrestors at tower base or house entrance?
From: Jim Lux <>
Date: Tue, 26 Feb 2008 17:52:27 -0800
List-post: <">>
Alfred Frugoli wrote:
> Dick said:
> With arrestors at the tower only, a surge could be induced in the portion of
> the cables leading from the tower to the house, and there would be no
> protection from the surge jumping right to the equipment inside the house.
> Dick also said:
> I have a set of arrestors at the bulkhead entrance, and another identical
> set at the tower. One reason is that I have SO2R switching equipment at the
> base of the tower and I wanted to protect it. Also, the run to the house is
> over 225 feet, which is a long way for a surge to travel before finding a
> path to ground. Seemed like a good idea to give it a shorter path to protect
> the long and very expensive cable runs.
> So I'm envisioning the following (--- being coax cables)
>      Tower-----arrestor at base of tower-----2x6 switch-----arrestor at
> bulkhead----equipment
> My question is what guarantee is there that any surge induced in the cables
> between the tower and the house is going to find the ground at the house end
> of the cables?  It could just as easily flow down the cable towards the
> switches/tower, in which case the switches are not protected. 

I think that you'd need another shield ground at the point where you get 
close to the equipment.  That way, any induced currents are on the 
"outside of the coax" and can flow "outside the shack" to ground.

Essentially, you've got your switch box in a little faraday cage or 
shielded room, with cable shields grounded where they penetrate the room 
wall, so induced currents on the outside stay outside.  Transient 
suppressors protect the contacts of the relays inside the box from 
overvoltages between center conductor and inside of the shield. (another 
discussion about what you're going to do with the relay control signals..)

Then, you have your equipment inside another faraday cage, where the 
cable shield is connected to the outside of the cage where it penetrates 
the wall.  (or, alternately, you have all your gear tied together so 
that if the shield voltage rises, everything rises together...)


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