CLASS H ELECTRIC MOTORS: characteristics and use

Class H Electric Motors

insulation classes and characteristics

Class H electric motors correspond to types used at high temperatures. The insulation class of an electric motor is mainly determined by the quality of the winding insulation. The windings of electric motors are normally insulated from each other by special resins in order to prevent short circuits and current leakage; these resins ensure that the motor runs smoothly until a given temperature is reached.

The insulation classes for electric motors are: E, B, F, H and C, to which correspond the permissible temperatures shown in the diagram below.

The insulation class of an electric motor is always indicated on the nameplate by the letter of the class itself.

The standard insulation class of an electric motor, normally used for most applications and machinery, is F. In some cases, however, it is recommended, if not necessary, to use electric motors with insulation class H (Class H motors).

The Class H electric motor is also referred to as a ‘high temperature motor’. The purpose of Class H insulation is to protect the various components of the electric motor from damage caused by overheating due to operation in high temperature environments.

Class H electric motors are constructed using, in addition to special dedicated resin, metal components, Viton sealing rings and C3 bearings with special grease (-30 °C to +140 °C).

Use of class H electric motors

The conventional ambient temperature for electric motors is set at 40°C; the permissible overtemperature (i.e. the temperature above 40°) for Class H electric motors is a further 125°C with a safety margin of a further 15°C.

To recap: 40°C ambient temperature in the standard operating temperature for all electric motors; 165°C (40°+125°C) standard operating temperature for Class H electric motors; 180°C maximum permissible temperature for Class H electric motors considering the safety margin.

Class H electric motors are therefore designed and constructed to withstand a maximum total temperature of 180°C.

Class H electric motors are mainly used in kilns and drying plants.

The application areas for Class H electric motors are therefore: ∙ Food ∙ Drying ∙ Glass Processing ∙ Wood Processing ∙ Plastic Processing ∙ Construction Manufacturing ∙ Ceramics ∙ Steel ∙ Painting ∙ Boilers.