The main component for electric motor is a stator.What is stator?Basically stators are wound with insulated windings made from cooper wire.The insulation  materials for winding of stator such as polyester, poly vinyl formal,polyurethane etc.

The main purpose of insulation is to protect the windings in the slots of the stator lamination and layer between winding coils.The insulation class is durability factor depend on whole of insulation condition.

According from IEEE regulation,The classification of insulation electric motor have a deference rating for maximum temperature that insulation winding can operate.We can see the insulation class at  motor nameplate.Please refer the table below for insulation class rating temperature. read more