0.86combined derating factor
6.4 kWrating needed for a 5.5 kW load
7.5 kWselected motor
The duty
A 5.5 kW pump at a site 2,500 m above sea level, with ambient air up to 45 °C.
Why ratings change
IEC 60034-1 ratings apply up to 1,000 m and 40 °C. Above that, air density falls and the cooling air is warmer, so the same losses raise the winding temperature more.
Typical derating factors
| Ambient | Factor | Altitude | Factor |
|---|---|---|---|
| 40 °C | 1.00 | 1,000 m | 1.00 |
| 45 °C | 0.96 | 2,000 m | 0.94 |
| 50 °C | 0.92 | 2,500 m | 0.90 |
| 55 °C | 0.87 | 3,000 m | 0.86 |
Combined factor 0.96 × 0.90 = 0.864
Rating needed 5.5 ÷ 0.864 = 6.4 kW → select 7.5 kW
A 5.5 kW motor here delivers only 5.5 × 0.864 = 4.75 kW
Using the thermal reserve
EMPD motors use Class F insulation with a Class B temperature rise. The 25 K reserve between the two can sometimes absorb a mild derating without a frame change; EMPD confirms this per rating by calculation, and by heat run where needed. Factors in the table are typical industry values; the final rating is confirmed for your site.
Application study: an engineering example worked by EMPD with catalogue data. Your application is confirmed by our engineers before quotation. Send us your duty.
