The AM Forum

I seem to remember through the haze and fog that even the best electrical grade aluminum only has roughly 40% of the conductivity of pure copper.

Can dis be confirmed or denied by teh AM Forum Brain Trust?

Here is an article on the sugject.

I think that electrical Al has about 60% of the conductivity of Cu.

But copper weights much more, so on a by-weight basis, Al has more conductivity per pound.

Most high power transmission lines are Al as weight is important. Al is also cheaper.

http://www.key-to-metals.com/Article116.htm

Yeah, with today's copper prices you can increase the cross-sectional diameter in an alum. wire very slightly for the same amount of current capability and at way less cost.

You do have to watch out for Alum. compressibility, oxidation at connectors, dissimilar metal corrosion at connectors, etc. 

Utilities routinely check all connections with an IR detector, looking for hot, bad joints.  Surprising what you find.  So a lot of houses don't use Aluminum wiring anymore except for the 240 utility drop on the E co's side of the meter.  But singing to the choir there; you knew that.

According to a table I just saw, copper has 58 times 10^6 mhos/m and aluminum is 37.

To get the same current carrying capabilty for AL versus copper. Increase the AL size wire by two. IE, #10 AL is the same as #12 copper. This holds tru in the motor and transformer rewind business. Mite not be the same in a "free air" circumstance.
Gary

biggest thing about aluminum is thermal coeff .... as it heats up it changes dimensionaly much more than copper ... can be tuff to keep connecting joints tight ... I still won't use it ANYWHERE in house wiring (inc breaker boxes) ... by the way, GE has been offering copper bar load centers ...the copper is an alloy ... I put in two of them and they run very cool ...beefus

any idea what the alloy is?

i got hooked on this back when I was pounding my ground rods down in the spring. grounding practices - DC vs. RF. etc really is a fascinating subject. I was looking in Mc. Master Carr and they have some 'electrical' AL alloy. So that got my mind thinking about it again, as well as finishing up the matchbox following the 'RF GROUNDS BACK TO ONE PLACE' method. Should be done by tonight, for good this time. 5/16" bolt, followed by internal copper buss bar. Silver strap for the rf and #6 solid for the DC. Check it with yaesu #1 and seal it up, all 47 screws.  :P

The two thousand feet of aluminum ground wire I put under the sod in 1977 is powder today. copper would last forever. 

Boy Frank,  that is a sad tale.  I guess the price was right on the wire at the time.  ;D

Way back when, I remember my father putting in an al. ground wire to a copper rod right below his bedroom window for a receiver gnd.   So I thought that peeing on it occasionally (we lived out in the country) would help the salt conductivity of the soil around the ground rod. 
   
About half a year later he wondered what varment had chewed off his ground wire right at the rod.

"Hmmm, yeah I wonder," said his lyin' son.

not sure what the alloy is but some related reading indicated it might be cadmium .... almost had a silver plated appearance but scratching thruthe surface showed no color change ... the bus bars where embossed with 'copper' so they were serious about it ... I clamped one of the feeders last winter on our coldest morning ... 153 amps on a 200 amp service ... I barely could sense any temp rise ...73...John

cadmium is expensive as hell. Just the plating solution for that metal is expensive as hell.

Frank,

When I had my first job out of school in Plantation FL, we rented a house on a canal. I put up a 20 ft aluminum base loaded vertical and threw a roll of # 10 aluminum wire right into the canal as my counterpoise. It was pitted in two days. Nasty stuff in the brine.

Mike