Re: If you are bored.....
Iwire:
Darned your good. I have been wondering for a while what the code would say about conductor of other materials, and I decided to post the question when I ran across 110.5 today.
But what about the last sentance "Where other materials are used, the size shall be changed accordingly." I guess that only applies to conductors that are not copper as "otherwise provided in this Code". (I'll tell Mr. Sly to have the panelboard made out of gold instead of the feeders
)
Since bph provided the numbers, I post what I was thinking. Al and Cu should have the same temp. for the same power loss per unit length (assume for a minute the thermal properties of both materials are the same). Power is proportional to (I^2) * R *C where R is the resistivity, and C is a constant. Do a little math (I'm a math geek as well as a code geek) and:
I(gold) = I(copper)*sqrt(15.8/20.11) = 176 amps for 3/0 at 75 deg.
For alumnium, I(alumnium) = I (copper)*sqrt(15.8/25) = 159 amps.
So the 159 amps is very close to table 310.16 value of 155 amps. I wonder if the small difference is due to different thermal properties of the materials that I assumed?
Steve