Impregnating resins are a key component of low voltage motor insulation but are not entirely designed keeping in mind their dielectric properties as they should withstand limited electrical stress. With power electronics, electrical stress can exceed the threshold for partial discharge inception leading to failure in short times. The reliability of the insulation thus becomes more dependent on the performance of the impregnating resins since impregnation raises the partial discharge inception voltage. We have investigated impregnating resins finding that, sometimes, perform in unexpected way at elevated temperatures. Besides, using an infrared camera, we have observed how impulse voltages having elevated slew rates impact on impregnated twisted pairs. The results suggest that bare twisted pairs do not change their temperature appreciably, whereas impregnated twisted pairs can display some increase in the temperature, signaling the presence of large dielectric losses.