NEMA A, B, C and D Design

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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.

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Related Topics

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

Related Documents

• Electrical Motor Efficiency - Calculating electric motor efficiency
• IEC - NEMA Standard Torques - Comparing IEC and NEMA torque classifications of electrical motors
• NEMA - National Electrical Manufacturers Association - National Electrical Manufacturers Association
• NEMA Frame Assignments - NEMA Frame Assignments
• Slip in Electrical Induction Motors - The difference between the synchronous and asynchronous speed - also named rated speed - is "the slip"
• Torques in Electrical Induction Motors - There are some common torques used to describe and classify electrical motors