BUYING AN ENERGY-EFFICIENT ELECTRIC MOTOR (2)

2. What is an energy-efficient motor?
Motor efficiency is the ratio of mechanical power output to the electrical power input, usually expressed as a percentage. Considerable variation exists between the performance of standard and energy-efficient motors (see Figure 1). Improved design, materials, and manufacturing techniques enable energy-efficient motors to accomplish more work per unit of electricity consumed.

Energy-efficient motors offer other benefits. Because they are constructed with improved manufacturing techniques and superior materials, energy-efficient motors usually have higher service factors, longer insulation and bearing lives, lower waste heat output, and less vibration, all of which increase reliability. Most motor manufacturers offer longer warranties for their most efficient models.
To be considered energy efficient, a motor’s performance must equal or exceed the nominal full-load efficiency values provided by the National Electrical Manufacturers Association (NEMA) in publication MG 1. Specific full-load nominal efficiency values are provided for each horsepower, enclosure type, and speed combination.
A motor’s performance must equal or exceed the efficiency levels given in Table 1 of this fact sheet (reprinted from Table 12-10 of NEMA MG-1-1993, Rev. 1) for it to be classified as “energy efficient.”
The Energy Policy Act of 1992 (EPACT) requires that most general purpose motors manufactured for sale in the United States after October 24, 1997, meet new minimum efficiency standards. These standards are identical to the shaded area of Table 1. The Act applies to 1- through 200-hp general-purpose, T-frame, single-speed, foot-mounted, continuous-rated,
polyphase, squirrel-cage, induction motors conforming to NEMA designs A and B. Covered motors are designed to operate with 230 or 460 volt power supplies, have open or “closed” (totally enclosed) enclosures, and operate at speeds of 1200, 1800, or 3600 rpm.


to be continued………..

Source : Fact Sheet – US Department of Energy
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