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Thyristor based, phase angle controlled, speed regulators are widely used for energy efficient control of single-phase induction motors. This leads to power saving but adversely affects the life of insulation in the motors due to distortions in the applied voltage and current waveforms. The accelerated insulation ageing is due to increased voltage peaks, voltage transients and increased thermal stress. Voltage harmonics increase dielectric and core losses. Current peaks increase the thermal stress in the insulation. This paper presents the application of fuzzy logic system to life estimation of the insulation of phase angle controlled single-phase induction motors. Three basic insulation degradation parameters; voltage peaks, rate of rise of voltage and thermal stress are used for life estimation. The results obtained with the fuzzy expert system for the set of experiments show a performance approaching that attainable for the life model based on the inverse power law.