NEMA B Three Phase Squirrel Cage motors – Locked Rotor Current

The National Electrical Manufacturers Association has defined different torque profiles for three phase induction motors. For example, design D offers high starting torque and might be advantageous in a drill or press application.

By far, the most common squirrel cage motor design is NEMA B which strikes a compromise between moderate starting torque and low slip speed (< 5% of at rated load).

For NEMA B motors, here is a listing of the maximum allowed locked-rotor current at 230V, as defined by MG 1 12.35.1. For values outside 230V, NEMA states “The locked-rotor current of motors designed for voltages other than 230 volts shall be inversely proportional to the voltages”. Which leads us to calculate the other values.