The three-phase induction motor is divided into four classifications
according to NEMA. (Note that there are IEC design standards
that differ somewhat from the NEMA versions.) The classification
or design is determined by the locked rotor torque and current,
breakdown torque, pull-up torque, and the percent slip. The speedtorque
curve and characteristics of each design are given below.
These characteristics apply for operation from fixed frequency
and voltage as normally supplied from commercial utility power
sources at 60 Hz