[RFEngineer]

“Electric current doesn’t use the center of a wire.”

Who told you this? With a DC motor it certainly does use the whole wire. With AC you have to be fairly high in frequency to produce “skin effect” that would negate the inside of a wire

[Reeses]

I stand corrected, electric current uses the whole wire. Layman books can be just as wrong as the internet.

Hollow wire cooling does seem to be a workable idea, allowing 50% smaller motors: DEF_Internally_Cooled_Hollow_Wires_ATZ-2017.pdf