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.
--
Art Greenberg
WA2LLN
art@artg.tv
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