60 Hz Efficiency
50 Hz Penalty in %
Typical reduction of energy efficiency in %-points for 4-pole, low-voltage motors between 50 and 60 Hz when compared at the same power (60 Hz torque 20% reduced)
For these reasons the limit curves in IEC 60034-30 of the different efficiency classes (IE1, IE2, IE3) are generally higher for 60 Hz motors than for 50 Hz motors.
A change in efficiency as a function of voltage is an inherent characteristic of motors. Operation of the motor at voltages substantially different from rated voltage will result in a change in motor efficiency and heating. Typically the efficiency of small motors suffers more from voltage deviation than that of larger motors.
Motors rated for operation at frequencies other than 50/60 Hz
Motors rated for operation at frequencies other than grid frequency (50 or 60 Hz) are not classified in efficiency classes according to IEC 60034-30. The efficiency class IE4 as defined in Annex A of this document is the only efficiency class applicable to such motors.