David, how far is your tower from the shack? I wonder about whether the
tower ground should be connected to your house ground with something other
than the shield of your coax cable(s). My thought is that if your tower is
located a ways from the shack then as a charged cloud moves overhead (or if
lightning strikes) the ground potentials at the tower ground and the shack
ground will be different. This will cause current flow between the two and
it'll take the least resistance path which will be down the shield of your
coax cables. It seems like it would be better to keep everything more or
less at the same potential by connecting both grounds together with some
heavy wire/cable/strap, and placing ground rods between the tower and shack.
That way most of the current (either from charge build up or during a
lightning strike) flows along the ground cable instead of on your coax. Bob
and I have gone round and round on this. He thinks it's a waste of money,
I'm not so sure. Does anybody else on this list have a strong opinion one
way or another about this?
thanks,
Dave
K0QE
----------
From: DavidC [SMTP:eDoc@netzero.net]
Sent: Thursday, December 09, 1999 8:57 PM
To: n7cl@mmsi.com; towertalk@contesting.com; aa0cy@nwrain.com
Subject: Re: [TowerTalk] Three Lightning Protection Clarifications
Please?
Thanks to all for the very helpful review of lightning protection
and grounding principles! Here is what I have learned from this
and am about to apply.
Context:
The only reason I am extending the ground is because the shack
entry point for antennas is 48 feet away from the service ground
rod.
I understand that I need to connect to that to avoid circulating
currents.
The tower will be heavily grounded so hopefully most of the energy
will be absorbed there. The ground here is said to be Alkaline
(sand,
some clay and limestone) and the test I just ran confirms that.
Plans:
I will go with copper ground rods and avoid complications. The wire
I
have is stranded and each strand looks to be about #10.
I am awaiting a reply from Harger as to the cost and part numbers I
need for the CADweld moulds, starter and materials. I am told that
Harger is 1/2 to 1/3 cheaper than all other sources.
I will have a grounding panel just outside the shack wall, about 24"
from the wall, through which all of the antenna and rotor lines will
be
routed. My one open-wire feedline will have both a disconnect knife
switch and inline AEI lightning protection fuses. The coax and
rotor
wires will have Polyphaser and MOV protectors. The panel will be
thoroughly bonded to the buried ground line that I will have
extended
from the service panel ground rod to the shack entry point 48 feet
away.
I think that about covers it.
- Thanks! & 73, DavidC K1YP
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