Insulation Temperature Limits
The National Electrical Manufacturers Association (NEMA) has established the average Insulation Life of motor insulation, based on maximum operating temperature, to be around 20,000 hours. NEMA classifies insulation into four different classes: Class A insulation has a recommended maximum operating temperature limit of 105 °C or 221 °F, Class B limit of 130 °C or 266 °F, Class F limit of 155 °C or 311 °F, and Class H limit of 180 °C or 356 °F. A good rule of thumb is for every 10° C rise above the established NEMA temperature rating, the motor insulation life may be reduced by half. The most common insulation class in the U.S. is Class B for 60 cycle motors and the most common class used internationally is Class F for 50 cycle motors.
To see effects of high temperature on motor insulation, Click Here to view the Some Like It Hot video.
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