NEMA ENERGY-EFFICIENT MOTOR STANDARDS (Electric Motor)

2.7
In 1990, based on the experience gained by the electric motor manufacturers in producing energy-efficient polyphase induction motors and interest by industry, NEMA adopted a suggested standard for future design defining energy-efficient motors and setting efficiency levels for energy-efficient motors. These standards are as follows:*
MG1-2.43 Energy Efficient Polyphase Squirrel-cage Induction Motor. An energy efficient polyphase squirrel-cage induction

TABLE 2.7 NEMA Nominal Efficiencies NEMA Table 12-6A

motor is one having an efficiency in accordance with MG1-12.55A. Suggested Standard for Future Design. MG1-12.55A Efficiency Levels of Energy Efficient Polyphase Squirrel-cage Induction Motors. The nominal full-load efficiency determined in accordance with MG1-12.54.1 and identified on the nameplate in accordance with MG1-12.54.2 shall equal or exceed the values listed in Table

TABLE 2.8 NEMA Table 12-6c Full-Load Nominal Efficiencies and Associated Minimum Efficiencies for Polyphase Induction Motors

TABLE 2.8 Continued

FIGURE 2.11 NEMA energy-efficiency standards for four-pole open induction motors from data in Table 2.8. (Courtesy National Electrical Manufacturers Association, Washington, DC.)

FIGURE 2.12 Comparison of NEMA nominal efficiency and available industry average efficiency for 1800-rpm open energy-efficient motors.

12-6c for the motor to be classified as “energy-efficient.” Suggested Standard for Future Design.

As mentioned earlier, the variation in the nominal efficiency of energy-efficient induction motors has been smaller than for standard induction motors. In addition, the electric motor manufacturers have experienced less efficiency variation in their product. This is reflected in the NEMA standard for energy-efficient motors, in that the variation in the allowable losses has been reduced to ±10%, which means a higher minimum efficiency for a given nominal efficiency. Table 2.8 is a copy of the NEMA Table 12-6C with the higher full-load nominal and minimum efficiency standards for energy-efficient motors, both open and TEFC, at various speeds. Figure 2.11 shows the relationship between the NEMA nominal efficiency and the minimum efficiency for energy-efficient four-pole open motors. Figure 2.12 is a comparison of the NEMA nominal efficiencies and the average of the available industry energy-efficient four-pole open motors. This indicates that available energy-efficient motors have efficiencies slightly higher than the NEMA standard.