208V / 220V 3PH machine tool motor running on 480?

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Phil Taylor

New User
Electronics Repair Man
I have a lathe in my shop with a two speed motor. Badge specs are 208/220V 0.5 HP at 550 rpm and 1.0HP at 1740 rpm.

The motor has 3 leads for low speed and 3 leads for high speed. no other windings are accessible.

The machine is wired 480 and supplies 480 to this motor, verified at the contactor.

Current draw measures actual 1.0A on low and 1.3A on high speed. Speeds are 594 rpm and 1790 rpm on my tachometer at the motor shaft.

I have heard of (and used) many 3 phase motors running off the wrong voltage (208 fed to a 440V motor e.g.) My understanding is that it works because of the permeability of the iron in the motor ... which limits the current to some degree allowing a completely mis-matched voltage to still work albeit with lower efficiency and worse output.

So, is it likely that I have a re-wound motor in this machine that was not labeled as such?

Or do I have a machine that is mis-wired and is actually feeding 480 to a 208/220 motor and it's getting by okay?

Again, I have seen 208 fed to 440 motors and it works, they just 'run slower' ... does the reverse work?

Phil in Delaware

Little Bill

Staff member
Tennessee NEC:2017
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