Aluminum motors vs. copper generators

The central counterexample. Aluminum has 2× the specific electrical conductivity of copper; used in motors but not in large generators.

That all sort of made sense — it's spinning, you want lightweight, and if it's got better specific electrical conductivity. The next morning while I was shaving, I almost cut myself, I realized: wait a second, that is not the criterion for selection of the material that you're winding the motors out of. At that time, 1987 or whenever this was, we were winding motors out of aluminum. Aluminum has a better specific electrical conductivity than copper. It's 40 percent lower electrical conductivity, but it's got one-third the density. So aluminum has twice the specific electrical conductivity of copper, but we were making motors out of aluminum.