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[Towertalk] Ground wire impedance

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Subject: [Towertalk] Ground wire impedance
From: (Tom Rauch)
Date: Mon, 29 Jul 2002 22:02:47 -0400
> There seems to be some debate over multiconductor wire for grounding. 
> As I see it, the only advantage of stranded cable is mechanical
> flexibility.  I don't think "skin effect" (current flowing on the
> surface) has much to do with stranded wire, since the strands are all
> touching and are all in each other's magnetic fields. What is good is

At high frequencies, for the same outer diameter, stranded wire has 
less effective surface area. That's because current pushes to the 
outer edges of each stand, and the wire has an air gap between 
strands that wastes space.

The finer the strands for a give wire size, the worse the wire 
becomes at high frequencies as a general rule. (Lightning has a large 
amount of high frequency energy.)

To see an example of this, look at loss specs for a given conductor 
size coaxial cable that has solid smooth conductors, coarsely 
stranded conductors, or fine thin multiple stands to make the cable 
extra flexible.

This is why you NEVER see finely stranded wire in well designed 
systems with high frequency high current applications like tank 

If the wire is woven into a braid, it really is a big problem. 
Resistance and inductance can go way up, especially if the braid is 
loose or dirty. That's the main reason coax gets so lossy when the 
braid tarnishes from moisture. The braid from RG-8 cable handles 
about the same 30 MHz current as number 16 or 18 solid wire. Better 
if dry and tight, and worse if loose or tarnished.

73, Tom W8JI 

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