[TowerTalk] Tower lightning ground system layout

[Les Kalmus]

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.
>