[Top] [All Lists]

Elevated cable runs

Subject: Elevated cable runs
From: W8JITom@aol.com (W8JITom@aol.com)
Date: Sat May 4 10:29:35 1996
In a message dated 96-05-03 20:50:31 EDT, you write:

>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.

That's part of what I was thinking of, the other part was RF induced currents
in the feeder.

The main difference between *proper* commercial installations and typical
Ham-type installation is grounding methods. Proper installations bring the
feeders and other conductors through a grounded bulkhead, and the entire
station is grounded to a common point...power mains, telco, antennas, and

Most Amateurs won't or can't do that, plus they have LF RF to contend with.

The safest system is to bring the feeders and rotor wires all down to ground
level and run them underground to the house.

73 Tom

>From n3rr@cais.cais.com (Bill Hider)  Sat May  4 11:14:34 1996
From: n3rr@cais.cais.com (Bill Hider) (Bill Hider)
Subject: Elevated cable runs
Message-ID: <199605041014.GAA11762@cais.cais.com>

Scott, don't install them above ground.  If you go underground at the tower,
either inside conduit or direct buried, you will have better lightning
protection.  This is  because of the capacitance to ground from the cables
through their insulated jacket to ground.  This will help bleed off the
lightning to ground before it gets to your shack/house/equipment.

If they are above ground, not only will any lightning voltage that is put on
the cables at the tower continue on the cables, but additional voltage, due
to a lightning strike to the tower, may be INDUCED onto the cables and stay
on the cables instead of being bled-off to ground.

There are also other considerations, such as lightning protectors, grounding
the cables at the top and bottom of the tower, and many other things to
consider when protecting a station/tower from lightning.  Catch my
presentation at the contest forum at Dayton and I'll go through what I did.



At 06:58 AM 5/3/96 -0400, Scott Detloff wrote:
>I'm getting ready to start running cables from my two towers.  They are located
>170' and 310' away from the house, and the plan is to use 8' 4X4's buried
>2' and spaced every 10'.  A "U" shaped bracket will hold a 1/4" guy wire on
>4X4, and the the cable runs attached to the guy wire.  There will be atleast
>five 3/4"
>CATV, and 6 control line/ rotator cables coming from each tower.  Any
>on your installation, or installations that you have seen would be greatly
>for tips.

<Prev in Thread] Current Thread [Next in Thread>