This paper presents an experimental evaluation of the voltage unbalances effects in the efficiency of induction motors. In that sense, two distinct National Electrical Manufacturers Associations (NEMA) design were evaluated to seek the changes on their performance. The voltage unbalance was assessed using the Complex Voltage Unbalance Factor (CVUF). The experimental methodology consisted in a segregation losses approach to study the stator, core, friction, rotor, and stray-load losses clearly. First, a no-load test was carried out in both motors keeping constant the magnitude and the angle of CVUF. Next, a load test was accomplished ranging the mechanical load from 120% down to 30% of the nominal load using the same CVUF of the no-load test. Finally, according to the results of NEMA design B motor has the greatest losses increment because it was the most affected by the skin effect.