The answer to this question is that it is not really a rating. It is the result of choosing a particular gage of wire and placing as many turns as possible inside a particular case. The amount of wire has a DC resistance and an inductance. When the stepper is "holding" the "rating" tells you a voltage and a current. Ohms law tells you the DC resistance of a winding. You can operate a stepper motor at any voltage as long as you use a series resistor to drop the difference between your supply and the voltage on the coil. As an additional benefit the L/R time constant goes down so that you can increase the speed. What you pay for that benefit is the heat dissipated in a 100W resistor, or whatever power level is required.Why are stepper motors rated at such odd voltages? i.e. 3.42v
Why not 5v, can a stepper rated at 3.42v be run at 5v?