We’re asked this question on almost every quote. The honest answer is that it depends on how many hours the motor runs and whether it runs on a drive. Here is how we work it out.
The difference in losses
At 250 kW and four poles, our NA-series IE4 motor is 96.4% efficient at full load and the NX-series IE5 is 97.3%. That gap looks small, but losses fall from about 9.3 kW to 6.9 kW, a cut of a quarter.
At part load the gap widens. Permanent-magnet motors keep their efficiency down to a quarter of full load, where induction motors start to fall away. Pumps and fans on drives spend much of their life there.
Worked example
- 250 kW pump running 8,000 hours a year at an average of 70% load
- Electricity at AED 0.38 per kWh
- IE5 saves about 21,000 kWh a year, worth around AED 8,000
- The IE5 motor costs about AED 17,000 more, so it pays back in a little over two years
Run the same motor 2,000 hours a year and payback stretches to nine years. That’s when we recommend IE4.
When IE4 is the better choice
IE5 motors need a variable speed drive to start and run. For a fixed-speed conveyor started direct on line, or a standby pump that runs a few hundred hours a year, IE4 is simpler and cheaper and still well above the legal minimum.
Send us the run hours and load profile with your quote request and we’ll show both options side by side.
