[TowerTalk] Copper Vs AL Was UV and WX deterioration of THHN insulation, and effects

[jimlux]

On 12/29/16 10:22 PM, Roger (K8RI) on TT wrote:
> How does the resistivity of the Copper Chloride (What you get with
> Chlorine and moisture  on the surface of the Copper wire) on the surface
> of the Copper wire compare to the resistivity of Aluminum wire?

I looked up conductivity of various copper compounds - copper oxides, 
copper chloride, etc.

They're all really high resistivity (not as high as Alumina), but more 
importantly, some of them do dissolve in water (to some extent), which 
changes their resistivity at DC (and RF, but it's a ion mobility thing), 
so you might see a tiny difference between dry and wet conditions.

High, here, means resistivities in the 1000s of ohm-cm bucket, which is 
where wet wood is  Compare to copper at 1.68 micro ohm-cm - that's 9 
orders of magnitude different.
Sea water is 20 ohm-cm
carbon is .005

In all cases, for any plausible thickness (up to the diameter of the 
wire), no significant current flows in the corroded layer..



  I ask
> as I've seen number of posts on newsgroups where Al wire was being used
> for radials.

Actually, aluminum wire would be a good choice for above ground antennas 
- it might be cheaper than copper, even if you buy larger gauge to make 
the resistance the same as copper.  You'd need to go up in diameter (not 
area) by a factor of 1.67 - that's about 4.5 AWG gauges.. (double 
diameter is 6 gauges)


>
> Roger (K8RI)
>
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