NEMA Design E Motors and Controls — What's It All About?

The NEMA Design E motor concept was developed as a result of three major driving forces. The standard for motors used in North America is MG1, Motors and Generators, of the National Electrical Manufacturer's Association (NEMA) [1]. The standards for most of the rest of the world are those of the International Electrotechnical Commission (IEC). One of the goals established by NEMA in recent years is to harmonize with IEC standards where possible. Part of the performance characteristics of the NEMA Design E motor was a result of this harmonization effort. The second area of influence is the emphasis in North America placed on energy conservation. For an electric motor this is accomplished by improvements in the motor efficiency. The third factor is ease of use. For the NEMA Design E motor to be used in existing applications it is necessary that the motor be physically interchangeable with existing motors, typically NEMA Design A or B. While the NEMA Design E motor may be a physical equivalent of a NEMA Design B motor, the differences in performance may require changes in control and protection equipment. The purpose of this paper is to present the performance differences between NEMA Design B and NEMA Design E motors and the impact chat chis may have on the control, protection and application of the motor.