Vince,
I’m not exactly sure where I first got this information. I checked my copy of
“The ‘Grounds’ for Lightning and EMP Protection” by Ron Block (originally
published by PolyPhaser and now out of print), but all I could find was a
statement that the law of diminishing returns applies to radials over 75’ –
i.e., most of the lightning energy is dissipated in 75’ or so. I have a feeling
that the issue might have come up in a conversation or email exchange I had
with Ron Block or his brother back in the late ‘90s. I think that may be where
I heard that over 75-feet the two ends don’t “see each other”. I’ll have to do
some serious digging in my email to check if that was the source.
But never fear, I managed to find another reference from Ron Block that backs
up what I said, albeit in slightly different fashion. Check out these links:
http://www.dxengineering.com/pdf/Lightning%20Protection%20P1.pdf
http://www.dxengineering.com/pdf/Lightning%20Protection%20P2.pdf
http://www.dxengineering.com/pdf/Lightning%20Protection%20P3.pdf
In Part III, page 54, second column, first full paragraph, there’s a discussion
of connecting the single-point ground and tower, where Ron states that when the
two are separated by over 100’ it may not be cost effective to bond the ground
systems together.
Although Ron’s book is no longer in print, here’s a link to an article by Ken
Rand that includes most of the important content:
http://members.rennlist.org/warren/LightningProtectionAndGrounding.pdf
73, Dick WC1M
From: vincek4jc@gmail.com [mailto:vincek4jc@gmail.com] On Behalf Of Vincent Weal
Sent: Tuesday, January 22, 2013 5:38 PM
To: wc1m73@gmail.com
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] bonding to AC power box or inside fuse panel?
Dick, I want to thank you for this post. I have been trying to find an answer
to this question for years, but no one seemed to have a definitive answer. Can
you tell me where I can find the article you referred to?
My tower is going to be 175 feet from the shack and I wasn't looking forward to
dropping all that dough on grounding wire!
73, Vince K4JC
> -----Original Message-----
>"Another example is bonding the tower ground to the single-point ground at the
>house. My first tower farm is 265' from the house. Being new to tower
>construction, I laid 265 feet of 1/0 ground wire in the trench running between
>the two locations in order to bond the ground systems. This was not cheap, to
>say the least (though it was before the big run up in copper prices.) Later, I
>read an article by Polyphaser that said if the ground systems are more than
>75' apart it does no good to bond them -- the wire inductance will be too high
>to make an effective connection. With this in mind, when I installed my second
>tower system in a different location 220' from the house, I did not run a
>separate ground wire. The Polyphaser argument made sense to me. Also, there
>are two runs of 1-5/8" hardline in the trench, and the gigantic copper shields
>on those babies surely provide a lower inductance path between the tower and
>house than a 1/0 wire would -- if, in fact, any wire has low enough inductance
>at that length to be effective.
73, Dick WC1M"
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