Thanks for the tips guys. It sounds like I can work off of this receptacle then, provided that the voltage is in an acceptable range, and I don't overload the circuit.

Also, thanks Mark about the tip about testing for and avoiding using the "wild" leg, if I do find one. If all three legs have equal voltage to ground, I guess it would mean the circuit is driven by the other ("Wye/Star"?) type of 3-phase transformer.

I already mentioned to Ray that there was some type of free-standing, industrial dough mixing machine plugged into this receptacle. Kind of like a KitchenAid on steroids.