Choices
Recommended Level of Efficiency for Three-Phase Motors
The annual energy cost to run a motor is usually many times its initial purchase price. An energy-efficient replacement motor is constructed using improved manufacturing techniques and superior materials. So it runs cooler, vibrates less, is longer-lived and has a higher power factor. Energy savings are typically in the range of 2-10%.
Failed motors can be rewound, but they’re not as efficient as a standard replacement motor. If a motor is operating at less than a .50 load factor (average horsepower used divided by its full horsepower rating), downsizing to an energy-efficient motor is usually economical. Motors should be sized to operate with a load factor approaching 90 percent. If over-sizing is required for peak loads, consider a correctly-sized motor backed up with a pony motor. Choices Compare motors using a consistent measure of efficiency:- Nominal efficiency is an average value obtained by testing a group of motors.
- Minimum guaranteed efficiency is based on nominal efficiency, but accounts for variations between motors.
- Apparent efficiency and calculated efficiency should not be used.
| Motor HP | Totally Enclosed Fan-Cooled and Explosion-Proof Motors Minimum Efficiencies | Open Drip-Proof Motors Minimum Efficiencies | ||||||
| Speed | Speed | |||||||
| 3600 | 1800 | 1200 | 900 | 3600 | 3600 | 3600 | 3600 | |
| 1.0 | 78.5 | 85.5 | 82.5 | 77.0 | 80.0 | 85.5 | 82.5 | 77.0 |
| 1.5 | 85.5 | 86.5 | 87.5 | 80.0 | 85.5 | 86.5 | 86.5 | 78.5 |
| 2.0 | 86.5 | 86.5 | 88.5 | 85.5 | 86.5 | 86.5 | 87.5 | 87.5 |
| 3.0 | 88.5 | 89.5 | 89.5 | 85.5 | 86.5 | 89.5 | 89.5 | 88.5 |
| 5.0 | 89.5 | 89.5 | 89.5 | 87.5 | 89.5 | 89.5 | 89.5 | 89.5 |
| 7.5 | 91.5 | 91.7 | 91.7 | 88.5 | 89.5 | 91.0 | 91.7 | 91.0 |
| 10.0 | 91.7 | 91.7 | 91.7 | 91.0 | 90.2 | 91.7 | 91.7 | 91.7 |
| 15.0 | 91.7 | 92.4 | 92.4 | 91.0 | 91.0 | 93.0 | 92.4 | 91.7 |
| 20.0 | 92.4 | 93.0 | 92.4 | 91.7 | 92.4 | 93.0 | 92.4 | 92.4 |
| 25.0 | 93.0 | 93.6 | 93.0 | 91.7 | 93.0 | 93.6 | 93.0 | 92.4 |
| 30.0 | 93.0 | 93.6 | 93.6 | 93.0 | 93.0 | 94.1 | 93.6 | 93.0 |
| 40.0 | 93.6 | 94.1 | 94.1 | 93.0 | 93.6 | 94.1 | 94.1 | 93.0 |
| 50.0 | 94.1 | 94.5 | 94.1 | 93.6 | 93.6 | 94.5 | 94.1 | 93.6 |
| 60.0 | 94.1 | 95.0 | 94.5 | 93.6 | 94.1 | 95.0 | 95.0 | 94.1 |
| 75.0 | 94.5 | 95.4 | 95.0 | 94.5 | 94.5 | 95.0 | 95.0 | 95.0 |
| 100.0 | 95.0 | 95.4 | 95.4 | 94.5 | 94.5 | 95.4 | 95.0 | 95.0 |
| 125.0 | 95.4 | 95.4 | 95.4 | 95.0 | 95.0 | 95.4 | 95.4 | 95.0 |
| 150.0 | 95.4 | 95.8 | 95.8 | 95.0 | 95.4 | 95.8 | 95.8 | 95.0 |
| 200.0 | 95.8 | 96.2 | 95.8 | 95.4 | 95.4 | 95.8 | 95.4 | 95.0 |
| 250.0 | 95.4 | 95.4 | 95.4 | 95.0 | 95.0 | 95.4 | 95.4 | 95.0 |
| 300.0 | 95.0 | 95.4 | 95.4 | 95.0 | 95.0 | 95.4 | 95.4 | 95.0 |
| 350.0 | 95.4 | 95.4 | 95.4 | 95.0 | 95.0 | 95.4 | 95.4 | 95.0 |
| 400.0 | 95.0 | 95.4 | 95.4 | 95.0 | 95.4 | 95.4 | 95.4 | 95.0 |
| 450.0 | 95.4 | 95.8 | 95.4 | 95.0 | 95.4 | 95.4 | 95.4 | 95.0 |
| 500.0 | 95.4 | 95.4 | 95.8 | 95.0 | 95.4 | 95.4 | 95.4 | 95.0 |
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