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Re: Topband: Outdoor cable trunking - opinions pse

To: "Keith Jillings \(G3OIT\)" <g3oit.keith@jillings.org.uk>
Subject: Re: Topband: Outdoor cable trunking - opinions pse
From: "Tom W8JI" <w8ji@w8ji.com>
Reply-to: Tom W8JI <w8ji@w8ji.com>
Date: Tue, 8 Oct 2013 10:02:14 -0400
List-post: <topband@contesting.com">mailto:topband@contesting.com>
Lightning strikes aren't common round here, and if there is one it's more likely to damage the trees or the house.


I don't want anyone to get the impression the lightning damage I get comes from lighting hitting my cables.

The damage I get is from ground loop currents that flow through the cables. The current opens the shield inside the cable by melting the foil and the shield. The better the grounded, the worse the problem becomes. The most unreliable cables I have are the cables out to the elements in my eight circle, because it has 6 or 8 buried radials at each vertical. I used to lose a cable or two every year.

I fixed it by plowing in a number 8 wire out from the hub to each vertical, and using a 50 foot coil of small cheap coax in a sacrificial choke where the feed for the eight circle branches off the 1500 foot or so long trunk bundle.

Damage to shields has nothing at all to do with direct strikes, but rather ground loop currents in the earth when lightning hits within several hundred feet of the cable at any point. The better the cables are grounded, the worse this type of problem becomes.
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