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[TowerTalk] More comments on lightning

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Subject: [TowerTalk] More comments on lightning
From: (Eric Gustafson Courtesy Account)
Date: Fri, 5 Jun 1998 11:26:40 -0700

>Eric, my tower is, for a number of reasons, adjacent to my shack, and my
>service entrance is at the diagonally opposite corner of my house. A
>90-100 foot run around the periphery of the house would be required to
>bond the tower ground to the service entrance ground. Would that still
>be effective even if I were to spend the effort & money? Or are there
>alternatives in this case? Short of moving the tower or service
>entrance, that is! 
>Chuck, N4NM

Ah!  A testimony to poor planning!  ;-)

You would probably be better off overall to route the feedlines to
the service entry first, do the ground panel there, and then
route them to the shack.  But if you do this, make sure first
that the tower base is adequately grounded (5 ohms or less).  the
feedline from the tower to the house can be brought in to the
panel high (under eaves, etc.)

Also, the cable routing and ground connection from the shack to
the service entry should be carefully thought out.  Don't bring
the cables up under the eaves and run them around the house.
That makes a nice loop antenna to couple to the magnetic fields
surrounding a stroke.  Put some 8 or 10 inch wide metal flashing
along the house footer and run the cables along that.  Minimize
the separation between the cables and the flashing.  Bond the
flashing pieces together.  Tie the flashing to service ground at
one end and station ground at the other.

The purpose of this low impedance ground connection from the
service panel to station ground is to have the pulse propagation
velocity for the ground connection be lower than (or at the very
least equal to) the pulse propagation velocity along the feedline
shields.  A good rule of thumb is to have three times as much
surface area involved in the ground strap than in the total of
the feedline shields.

Anyone doing this kind of installation should consult the
applicable codes and heed their recommendations.

73, Eric  N7CL

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