[TowerTalk] Re: Static, Lightning, and protection

["Mark ." <n1lo@hotmail.com>]

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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