This IEEE Standards product is part of the C57 family on Power Distribution and Regulating Transformers. A test procedure for determining the temperature classification of ventilated dry-type power and distribution transformer insulation systems by test rather than by chemical composition is established. The intent is to provide a uniform method for providing data for selection of the temperature classification of the insulation system, for providing data that may be used as a basis for a loading guide, and for comparative evaluation of different insulation systems. Voltage-withstand endpoint criteria are related to the impulse voltage distribution within the coil or to the initial voltage-withstand of the coil. A relationship between impulse withstand of the insulation and short-term 60-Hz-withstand is identified so that 50/60--Hz testing of model coils is possible.