[TowerTalk] Re: Static, Lightning, and protection
Mark .
n1lo at hotmail.com
Tue Mar 23 08:15:48 EST 2004
Hi All,
When I was researching my tower, I ran into the same controversy as to which
protection scheme worked best. I decided to adopt more than one.
A prerequisite, of course, is to have a good lightning ground on the tower
base. Plenty of good discussion on that here.
I use static dissipator devices to help prevent some strikes, *AND* and air
terminal to provide a preferred path to ground for strikes that eventually
do occur.
An old timer's trick I learned about here, was to leave a tail on each guy
cable at the tower end, clamp/bond the tails to the tower legs, then unfurl
them and point them roughly 45 degrees up and away from the tower. I also
cut the ends of each EHS strand at 45 degrees to create sharp points.
With three sets of guy cables, this gave me 9 easy-to-construct, grounded
dissipators, distributed along the tower height.
But these cannot act as an air terminal, since the small strands would
surely melt if a strike did occur.
For an air terminal, I put a ground rod pointing up at the top of the mast,
higher than anything else. I had read of so many VHF/UHF verticals at the
top of masts being blown to smithereens, so It made sense to me to have a
heavy conductor instead.
Having the air terminal extend beyond structures you want to protect also
caters to the ball theory of lightning which proposes that when lightning
does occur, it will tend to hit the most extended/exposed parts of a
structure.
I also subscribe to the disconnect theory, keeping all conductors from the
tower shunted to a simple, low impedance bonded entrance panel when I'm not
operating.
So far, so good, after 5 years. Hope this helps some of you.
--...MARK_N1LO...--
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