They are
NEMA design A
maximum slip of 5 %
medium to high starting current
normal locked rotor torque
normal breakdown torque
suited for a broad variety of applications
Typical applications : fans and pumps
NEMA design B
maximum 5% slip
low starting current
high locked rotor torque
normal breakdown torque
Typical Applications
common in HVAC application with fans, blowers and pumps
NEMA design C
maximum 5% slip
low starting current
high locked rotor torque
normal breakdown torque
Typical application : High inertia starts - as positive displacement pumps
NEMA design D
maximum 5-13% slip
low starting current
very high locked rotor torque
Typical application : cranes, hoists etc.