Twelve-pulse drives are frequently specified by consulting engineers for heating, ventilating and air conditioning applications because of their theoretical ability to reduce harmonic current distortion, but very little information has been published showing how twelve-pulse drives perform under actual operating conditions with unbalanced input line voltages. This paper presents test data which demonstrate that twelve-pulse drives do not achieve the level of harmonic mitigation most engineers expect and that these drives may not meet the requirements of IEEE-519 under practical operating conditions. The actual performance of twelve-pulse and six-pulse drives is compared to the performance of a six-pulse drive fed by a Matrix Harmonic Filter. The Matrix Harmonic Filter provides superior harmonic mitigation at lower cost.