[TowerTalk] Grounding with Polyphaser lightning arrestors

[Larry]

As I recall having the rods too close was less effective in its ability to 
dissipate the strike charge. It wasn't a pure resistance idea although that 
is also a consideration.

It has been awhile since I read about the distance and, alas, my memory 
isn't what it used to be.

73, Larry  W6NWS
----- Original Message ----- 
From: "jimlux" <jimlux at earthlink.net>
To: "Larry" <w6nws at arrl.net>
Cc: <towertalk at contesting.com>
Sent: Tuesday, October 07, 2008 7:53 AM
Subject: Re: [TowerTalk] Grounding with Polyphaser lightning arrestors


> Larry wrote:
>> I believe it was the Polyphaser book that suggested that ground rods 
>> should
>> be spaced no more than twice the length of the ground rod. So, for common 
>> 8
>> foot ground rods the spacing should be not more than 16 feet apart. There
>> was a rationale to the spacing but it escapes me at the moment -  charge
>> distribution during a strike most likely.
>>
>
> more like that if you put them closer, the effectiveness (measured as DC
> resistance) is less.  Two rods close together have a DC resistance
> (referred to infinitely far away) more than half the resistance of one
> rod.  The limiting case would be if they were driven touching each
> other, which would have a resistance roughly the same as one rod.  Get
> them two rod lengths apart, and the resistance is "close" to half that
> of one rod.
>
> Why not put them hundreds of feet apart then?
> In lightning protection, though, you also want to minimize the length of
> the wires to the rods (because of the R and L of the wire). And, wire is
> expensive.
>
> So, about two rod lengths apart is a good compromise.
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