NEMA Motor Ratings

The National Electrical Manufacturers Association (NEMA)  has classified motors design in the following manner based on starting current, rotor torque, breakdown torque and slip.

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.


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