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Re: [TowerTalk] Tower lightning ground system layout

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Tower lightning ground system layout
From: Les Kalmus <w2lk@bk-lk.com>
Date: Mon, 18 May 2020 17:33:32 -0400
List-post: <mailto:towertalk@contesting.com>
My 89' UST with a tall mast and lots of antennas was professionally installed and had 4 #2 solid copper "radials" about 25 feet each. First, antennas on this tower worked really well and second, I am certain I took a major lightning hit on that tower but never had a problem. Each coax was lightning protected at the tower base and again inside the house. I wasn't able to have an outside cable entry box with ground like I wanted so all the cables passed through a second set of lightning protection mounted on a large heavy duty grounded panel inside the house right next to the cable entry point. The tower protection was several Alpha-Delta lightning arrestors and in-house ones were ICE. The house and shack were all connected to a single point ground of #2 copper and several ground rods outside the house.

That big strike did a pile of damage to electrical circuits, my security system and a couple of TVs and related equipment but nothing to any of my ham gear.

I would do it again exactly the same way.

Les

On 5/18/2020 3:28 PM, Art Greenberg wrote:
I am working on the layout for my tower lightning ground system.

I have on hand about 275 feet of #2 bare solid copper. I also have 17 8-foot 
ground rods.

I've read that lightning protection "radials" reach the point of rapidly 
diminishing returns at lengths beyond about 70 feet.

Originally I planned to have three runs of 50 feet about 120 degrees apart and 
make a fourth run go to my entrance panel and mains ground. But it seems my 
distance estimating skills are lacking. I just measured that distance and its 
more than 100 feet, and well beyond being an effective length.

If I instead go with four runs of about 65 feet spaced at about 90 degrees, the 
fourth run will be limited in length by a driveway. I can't rotate the whole 
pattern very much to improve that due to another obstacle. My apparent options:

1 - I can abandon the idea of equal angular spacing to make that run a bit 
longer. I think I can get the full 65 feet but I'll be going into a wooded area 
with the possibility of having to deal with shallow tree roots and I definitely 
won't be able to make a perfectly straight line of it.

2 - I can turn it into two or three shorter runs in a fan configuration (also 
abandoning equal angular spacing), but the angular spacing between the fan runs 
will result in the set ground rods on each run that are 16 feet from the base 
of the tower being much less than 16 feet apart. I imagine the optimal spacing 
rule of 2 times rod length still applies.

3 - I can put a bend in a single run to turn it parallel to the driveway to get 
the full 65 feet. I would have to abandon equal angular spacing to avoid an 
acute (less than 90 degrees) bend. What would be the best way to lay out this 
bend (e.g., multiple gentler bends vs. a single bend, smooth curve or something 
else, what about ground rod placement, etc.)?

Any of these options means acquiring more ground rods. I think I have a 
sufficient number of Uni-Shots already.

I'm thinking option 1 is best, but I'm uncertain. Is there a clear advantage to 
one approach vs. the other?

While I'm asking ... Should I be thinking about using more shorter runs, say 5 
runs of 55-ish feet spaced 70 degrees apart, or 6 runs of 45-ish feet spaced 60 
degrees apart?

Yeah, I'm probably over thinking this. But I live in Florida and summer 
thunderstorm season is about to begin.

Thanks.

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