This paper deals with the effect of simultaneous voltage unbalance and over- or undervoltage on windings temperature and thermal loss of life of an induction cage machine. The presented results of investigations are based on the experiment and thermal modeling. The influence of an angle of the complex voltage unbalance factor (CVUF) on machine heating is considered. The effect of synergy of voltage unbalance,and voltage rms value deviation is presented. Two induction machines of different properties are compared. One of them has a comparatively weakly saturated magnetic circuit, and the other a comparatively strongly saturated circuit. The former is especially exposed to overheating in the conditions of undervoltage, and the latter in the conditions of overvoltage.