NEMA A, B, C and D Design

NEMA has established four different designs - A, B, C and D - for electrical induction motors

Different motors of the same nominal horsepower can have varying starting current, torque curves, speeds, and other variables. Selection of a particular motor for an intended task must take all engineering parameters into account.

The four NEMA (National Electrical Manufacturers Association) designs have unique speed-torque-slip relationships making them suitable to different type of applications:

NEMA design A

  • maximum 5% slip
  • high to medium starting current
  • normal locked rotor torque
  • normal breakdown torque
  • suited for a broad variety of applications - as fans and pumps

NEMA design B

  • maximum 5% slip
  • low starting current
  • high locked rotor torque
  • normal breakdown torque
  • suited for a broad variety of applications, normal starting torque - 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
  • suited for equipment with high inertia starts - as positive displacement pumps

NEMA design D

  • maximum 5-13% slip
  • low starting current
  • very high locked rotor torque
  • suited for equipment with very high inertia starts - as cranes, hoists etc.

Related Topics

  • Electrical - Amps and electrical wiring, AWG - wire gauge, electrical formulas, motors and units

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