This paper examines the behavior in total losses and the efficiency of induction motors when supplied with frequency converters. The analysis of tests conducted in the laboratory on two induction motors of different power and efficiency classes is presented, following the methods 2-3A and 2-3C of the IEC60034-2-3 technical specification. Furthermore, the effect of increased switching frequency of the converter on the losses of both motors was experimentally evaluated. The results reveal an increase in losses when operating with the frequency converter compared to losses under balanced sinusoidal conditions. While both methods demonstrate this increase, method 2-3C estimated higher total losses, and therefore lower efficiency, than method 2-3A. Additionally, it was observed that the increase in the switching frequency of the frequency converter leads to lower losses compared to those obtained with lower switching frequencies. The increase in total losses due to supply with frequency converters must be taken into account when calibrating motor protections and when assessing efficiency improvements using frequency converters.