[TowerTalk] aluminum radials was Re: Copper wire prices

[Jim Lux]

At 05:19 PM 11/20/2006, k6xyz wrote:
>That's right Don.....
>Spend more $$ on the front end and save much more on the back end.
>I'm pretty sure that aluminum house wiring is illegal most everywhere
>now....

We drift a bit off topic here.. but..
CPSC says that roughly 2 million houses (out of the 107 million in 
the US) were wired with aluminum wiring.
http://www.cpsc.gov/cpscpub/pubs/516.pdf

It's not actually illegal.. The NEC allows use of aluminum wire in 
sizes AWG12 and larger, but nobody actually makes it in sizes smaller 
than AWG8 or AWG6.  It's still quite common for high current branch 
feeders, where the cost differential is significant, and, because 
it's a somewhat unique application, the odds of proper installation 
are higher.  Modern aluminum wire is also a different alloy than the 
stuff used in the 60s and 70s.

The original problem wasn't aluminum wire per se, but that the CTE of 
aluminum and steel (used in the terminals) is different, and aluminum 
has different mechanical properties than copper.  It's really not 
suited to being wrapped around a screw terminal. Around the same 
time, (also for cost reasons), most wiring devices went from brass 
terminals to steel and plated steel, aggravating the problem. And, 
notwithstanding the successful use of aluminum in distribution and 
transmission for decades prior to this (and since), the applications 
really are different, both in terms of typical connection methods and 
in the skill sets of the installers.

Modern aluminum conductors use a different scheme for clamping (an 
aluminum lug with a screw that clamps the wire), as well as a 
substantially different alloy, so you don't have the material 
properties issues.

Jim, W6RMK