Electric motors NEMA design

Motors are classified by size, apphcation, electrical type, NEMA design letter, and environmental protection and cooling methods. They are rated for special standard environmental and operating service conditions by performance and mechanical configuration voltage and frequency, locked-rotor kVA, service factor, horsepower, speed, torque, locked-rotor current, performance, temperature rise, duty cycle, and frame size. 

FIG. E-1 Speed-torque curves for a 5-hp motor, NEMA design A and D, and full-load efficiencies. (Source Reliance Electric.)... 

Energy Efficient (EE) Motor Designs, 628 NEMA Design Classifications, 630 Classification According to Size, 630 Hazard Classifications Fire and Explosion, 631 Electrical Classification for Safety in Plant Layout, 647 Motor Enclosures, 649 ... 

In addition to the above, NEMA designates a special class of Premium Efficiency Electric Motors (2003) for three-phase induction motors applied to municipal or industrial applications for operation on voltages of 600 V or less, rated 500 HP or less, operating more than 2000 hr/yr at more than 75% of full load. For details, please refer to NEMA MG 1-1998 Table 12-12. For each HP rating, that table defines nominal and minimum efficiencies for 2-, 4-, and 6-pole open motors. 

Each motor is given a test per NEMA MG 1-20.46 to prove freedom from electrical or mechanical defects and provide assurance that it meets design specifications. This test consists of the following ... 

Machine Design, Electrical and Electronics Reference Issue, sec. 7, Motors, May 17,1979, pp. 7 2. NEMA Standards Publication MGl-1993, Motors and Generators, National Electrical Manufacturers Association. Washington, D.C., 1993. 

NEMA (National Electrical Manufacturers Association) electrical design B, C, and D are most common and represent torque characteristics of the motor. 

Three-phase motors have a high starting torque, high efficiency, and low current requirement The torque characteristics are described by NEMA electrical design, which is discussed in the next section. Three-phase motors do not use a capacitor, switch, or relay for starting. 

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