NEMA A, B, C and D Electrical Motor Design
NEMA has established the four different designs A, B, C and D for electrical induction motors.
Different motors with the same nominal horsepower may have different start current, torque curves, speeds and other variables. When selection a particular motor for an intended task all engineering parameters must be taken into account.
The four NEMA (National Electrical Manufacturers Association) designs have unique speed-torque-slip relationships - making them suited for 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 - like 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 with normal starting torques - 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 and high starting torques at start - like positive displacement pumps, conveyors
NEMA design D
- maximum 5-13% slip
- low starting current
- very high locked rotor torque
- suited for equipment with very high inertia starts - like cranes, hoists etc.
