All standard 2-pole and 4-pole low-voltage three-phase motors (e. g. asynchronous motor) with power ratings from 1 to 1000 kW are categorised in efficiency classes in accordance with their efficiency.
Four different classes have been defined: IE1, IE2, IE3 and IE4. IE4-classed motors have the best efficiency; this is the class for energy-saving or high-efficiency motors. Older motor models without efficiency specification are included in class IE1.
See Fig. 1 Efficiency class
The motor efficiency (η) is calculated on the basis of the ratio between the shaft output power (POUT) and the electrical input power (PIN). The difference results from internal motor losses.
See Fig. 2 Efficiency class