Class "B" vs. Class "F" Insulation

Class "B" vs. Class "F" Insulation

Question: After requesting a motor equipped with class "F" insulation, I received a unit on which the insulation class is labeled "B." Was there a mix-up in my order?

Answer: No, there was not a mix-up. U.S. Electrical Motors builds all of their motors with class "F" insulation or better. When the nameplate indicates class "B", this means the motor is designed to operate within class "B" temperature rise limits. These limits are 80 degrees centigrade at 1.0 service factor, and 90 degrees centigrade at 1.15 service factor. For many years, it has been USEM’s policy to nameplate open dripproof motors that meet this temperature rise criteria with the insulation class "B", regardless of the actual insulation type. This gives the end user the information that the motor has a 90 degrees centigrade, or less, temperature rise at 1.15 service factor.

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