[TowerTalk] TT SHUTDOWN (was: 4 awg copper wire and Amp locks)

[Martin Ewing]

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.

> 
> I wonder... if you roll (the long way) copper strap you could put it inside
> hose.  As long as the inside circumference of the hose was greater than the
> width of the strap you wouldn't be forming a tube with the strap.  What if
> you slit the copper tube before using it, would that be enough to allow both
> the inside and outside to conduct high frequency current?

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?)

> 
> Just some thoughts.
> 
> 73 - JC, K0HPS
> 

73 Martin AA6E