What are the maximum temperatures that are guaranteed by the insulation classes?

Class Temperature in °C
Y 90
A 105
E 120
B 130
F 155
H 180
C >180

The thermal class of an electrotechnical product, a transformer for example, shows the maximum temperature at which the insulation materials and systems guarantee thermal stability compared to the age of the product. The thermal classes and their corresponding temperatures are mentioned above. These temperatures refer to the actual temperatures of the insulation material and not to the heating of the transformer or to the maximum ambient temperature.