In a message dated 96-05-03 19:32:54 EDT, you write:
>I think the potential problem (pun intended) being alluded to is the
>fact that a cable brought in above the ground may not be at
>ground potential. I believe the key is to bring it to physical (and
>electrical) ground first at the tower base before running it in.
>As a simplified example, if you have a 100 ft tower, and bring the cable
>down to 10 ft, then run it into the shack, you may retain 10% of the
>voltage of a lightning strike on the cable. This is (as I'm sure you
>know) because the tower appears as an inductance to the quick pulse of a
>strike, and the cable at the 10 ft level appears as a "tap" 10% above
>ground potential of the tower/inductor.
>As long as the shield of the feedline is grounded at the tower BASE, the
>way the cable is carried into the shack is irrelevant.
Okay, Barry --
I'll buy that. The commercial installations also have the feedline
grounded in 3 places; at the top of the run on the tower, at the bottom of
the run before the cable turns to go under the cable race and then at the
building entry (which is the Single Point Ground System focal point). If
hams did this (and a couple of other ground things), most lightning problems
would be eliminated.
BTW if anyone is interested, I have a draft copy of an article I wrote
on ground systems for amateurs. Send me your postal address and I'll be
happy to send a copy.
73, Steve K7LXC
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