While a large amount of information has been gathered on thermal and environmental aging of magnet wire films, and on the effects of corona and electrical discharge on sheet and film dielectrics, very little has been published on the effect of sustained voltages on magnet wire insulations. Under field use conditions many of these films encounter continual voltage stresses of considerable magnitude as well as extremely high voltage surges of short duration. The effect of these conditions on insulating materials has a significant bearing on how well and how long electrical equipment will continue to operate efficiently.