|Subject:||Re: [TowerTalk] TT SHUTDOWN (was: 4 awg copper wire and Amp locks)|
|From:||Martin Ewing <firstname.lastname@example.org>|
|Date:||Wed, 12 Jul 2006 11:20:29 -0400|
JC Smith wrote:
Gary's right although copper strap can be overpriced depending on where you find it. Copper tubing is such a common commodity it's hard to overprice it. One other advantage tubing has is it's easy to protect from weedwackers, lawnmowers (not the blades), etc. Just run it inside a length of thick hose.
If you are running strap in order to make a ground, you don't want to insulate it -- at least when it's running underground. Maybe you are referring to runs above ground.
You get minimum impedance when the strap is flat. If you roll it up, it is no better than thin wall tubing - i.e., there is no current on the inside. Impedance per foot is roughly doubled. A narrow slit on tubing won't change things at all, since all the current flow is longitudinal. Pound for pound of copper, you get the best ground with a wide flat strap, maybe 10 skin depths thick. You get the least effective ground by compressing it into a circular rod (wire). Hollow tubing is a little better.
Basically all the interior copper (below the skin depth) is wasted for AC current flow. Of course, it does give you better physical strength and thermal mass. (A low impedance ground isn't much help if it gets vaporized. Has anyone done a thermal analysis for very thin strap in a lightning surge?)
73 Martin AA6E
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