This paper addresses the technical issues in the energy efficiency assessment for inverter-fed motor drives according to the international technical standard (TS) IEC 60034-23:2013. The critical points on the TS procedure are investigated by means of experimental results, with special emphasis on the influence of the DC bus voltage, the thermal aspects, the dead-times influence and compensation on the measurements suggested by the TS. For an easier fulfilment of the thermal constraints on the maximum winding temperature variation during the test, imposed by the Norm, a very simple thermal network is proposed. The model is also useful to evaluate the time duration of the experiment. The results of the experimental activity performed on two different induction motors are included in the paper.