A guide to thermal classes (Class F, H, etc.) for enameled copper wire.

Magnet wire may look like bare copper, but it is coated with a microscopic layer of enamel insulation. The quality of this enamel dictates the maximum operating temperature of the motor before it shorts out.

Thermal classes define these temperature limits. Class B insulation is rated for 130°C, Class F is rated for 155°C, and Class H is rated for an impressive 180°C. Industrial environments often demand Class H wire to survive continuous heavy loads.

When rewinding a motor, always match or exceed the original thermal class. If a motor burned out under normal conditions, upgrading from Class F to Class H wire can significantly extend the lifespan of your repair job.