3-phase AC motors are much smaller and use less copper for the same torque than
1-phase AC motors, they also have less losses (are much more efficient) because
the AC line provides the phase rotation, rather than something (capacitor, imped
ance,etc.) in the motor providing phase rotation.

For a given amount of power transmitted across a distance, you can use much less
 copper for the same losses with 3-phase (3-wire), and you can use lower voltage
s = smaller, lighter insulators) because the wire is being used at the peak curr
ent (peak of the sine wave, where most of the actual power is moved) three times
 as often.

Finally with 3-phase, you can suffer the loss of one wire and still get apprecia
ble power to the destination.
  Regards,
    Ron Fial

=================================================
At 05:37 PM 7/21/98 -0400, you wrote:
>Hi All,
>
>Yeah, I know, its something that I should probably know already, but I
>have never seen an explanation, so I'll ask anyway:
>
>Does anyone have a quick explanation on why it is better (more
>efficient?) to use 3 phases instead of two on industrial equipment?
>
>Thanks,
>
>Sean
>
>