Thermal classification of magnet wire in NEMA MW-1000

Film insulated magnet wire was the first type of electrical insulating material to standardize a thermal life procedure based on the original work of Dr. Thomas Dakin.¹ The procedure was developed by AIEE/IEEE in the 1950´s and adopted by NEMA, ASTM and IEC in the 1960´s. The expansion of the general aging procedure and the evaluation of other insulating materials has resulted in the development of various guidelines which have been refined through the years. This paper traces the evolution of magnet wire thermal life testing and outlines the method used by the NEMA Magnet Wire Committee to establish a thermal class for each magnet wire product standard recognized in NEMA MW-1000, the NEMA Magnet Wire Standard.²⁶