Because variable-frequency drives (VFDs) adjust boththe output frequency and the voltage to their connected motors,the motor efficiency with a VFD is mathematically determinedby motor loads, frequency, and voltage. Several researchershave discovered that not only motor load but also VFD outputfrequency affects motor efficiency. The purpose of this paperis to investigate the impact ofVFDoutput voltageonmotor efficiencyby measuring the motor efficiency under various voltages.Theexperiment resultsshowthat the voltage also impactsthe motor efficiency and the manufacturer motor efficiencydata cannot be applied to the motors with VFDs.