[Towertalk] Lightning

[Pete Smith]

At 06:36 AM 5/15/02 -0400, Mel Martin wrote:
>I don't agree with this at all... I've taken a number of direct hits with
>minimal damage... You cannot protect 100%, lightning is somewhat
>unpredictable, but you can mitigate the odds considerably.
>I have a 150' tower in a very flat area.... the tower is the highest thing
>for miles I've had more damage to my C-band satellite TV system due to EMP
>than to the ham shack.
>
>BTW, commercial installations have to survive multiple direct strikes....

Yes, but commercial installations are designed from scratch to do this.  If 
you look at the illustrations of "typical installations" in Polyphaser 
literature you see very short, broad copper strap connections from the 
entry bulkhead to a building perimeter ground, equipment placed in the 
enclosure for short lead lengths to the bulkhead, and a host of other 
measures intended to keep the equipment ground at real ground.  Compromise 
that, and you've spent a lot of money for a false sense of security.

My shack is on the second floor, so I began with the assumption that I 
cannot get a good enough ground up here.  I did what I could as far as 
tower grounding was concerned -- though I could do more with coax shields 
at top and bottom of the tower -- but my real line of defense is 
disconnecting everything, because I assume that if a strike gets inside 
things will get fried.

By the way, the local power company installed a whole-house surge 
protector, and charges me $3.95 a month rent for it.  Cascaded with UPSes 
and surge protectors in the shack, I believe that gives me more protection 
than anything else I can do, because our power lines in this area are all 
above ground and thereby vulnerable both to direct hits and induced 
voltages from nearby strikes..

73, Pete N4ZR

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