4.5.1 Motor output rating categories

Induction motors are divided into three broad output power categories in NEMA MG1-1993, Revision 4: small motors; medium motors; and large motors. Small motors are fractional-horsepower motors. Medium motors are integral-horsepower motors, 1 hp through 500 hp in size depending on the speed and number of poles and in maximum ratings given in Table 4.8. Large motors are motors in the horsepower range from 100 hp through 50,000 hp shown in Table 4.9. NEMA MGl covers large motors for all the ratings in Table 4.9 at speeds of 450 r/min or slower. For higher speeds, only ratings greater than those given in Table 4.10 are included.

Since medium motors are used in very large quantities, much of the performance and dimensions...