the Insulation classes divide insulating materials into temperature ranges for which they are suitable. The insulating materials lose their effectiveness due to the constant heat loss from the electric motor, transformer, generator and electrical device.
This chemical aging process is accelerated exponentially with increasing temperature. It is therefore necessary to use insulation materials and impregnating agents of the appropriate insulation class in order to achieve a sufficient service life of the insulation.
Further information on the insulation classes can be found in IEC 85, IEC 216, and VDE 0530, Part 1.