To: <towertalk@contesting.com>
> Date: Thu, 28 May 1998 22:42:25 -0400 (EDT)
> From: K7LXC@aol.com
Hi Steve,
> " A nice low impedance path from the tower to the house" is a good
> start. Yes, it's not a 'ground system' but it's something that needs to be
> done.
You are welcome to do that at your house, but I won't do that as a
"rule" at my house or at most of the commercial installations I
oversee.
My closest tower is two feet from the house, and 60 feet tall. It
is intentionally located near and bonded to the service entrance of
power and telco lines, and has a driven rod and a small radial ground
system. It contains TV antennas and a two meter antenna, and all
cables enter with the telco and power cables, and share common
grounds just outside the house.
My next closest tower is 250 feet from the house, and 200 feet tall.
It is grounded by many thousands of feet of radials covering a ten
acre pasture. That radial field cuts off before reaching the power
line ground and house.
At my "last line of defense" at the edge of the pasture, I have
lightning retarding chokes both before and after a separate
driven rod independent ground. When I know of a storm, or when I go
away, I pull the plugs on ALL the cables at that point and pull
them back several feet.
The last thing in the world I want is to bring any direct strikes
that might elevate the earth around the tower into the house, where
the current might cause problems. I want to minimize coupling between
the tower and tower ground and the house and house ground, while
letting EVERYTHING in the house rise together and everything at the
tower do the same.
>What a 'lightning protection system' should do is have everything
>bonded
> together to minimize potential differences. It's these potential differences
> that cause the arcing and assorted damage to equipment.
That's true IN the house, or ON the tower, but you certainly don't
need to make the house ground follow the tower ground if you can
avoid it. If the tower is right against the house, the best idea is
to bring grounds and cables all up together with minimal potential
difference. If the tower is remote from the house, keep the grounds
isolated but STILL use the common point method at each end of the
system.
If the distance is greater, the problem becomes one of isolated
systems. Keep them that way if possible.
73, Tom W8JI
w8ji.tom@MCIONE.com
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