NEMA Insulation Classes

Class dismissed.

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Is the motor rated 50/60Hz?

This means that the motor is manufactured with class F insulation. But its cooling circuit will be so designed that the temperature rise of the motor is not allowed to exceed 130 degree celsius, although the motor can withstand 155 degree. This will provide a substantial margin for temperature rise and the expected life of insulation of the motor will be more.

A class 'B' insulating material will give a service life of about 20, 000 operating hours, at its maximum permissible temperature of 130 deg. C, under standard conditions of instllation, operation & maintenance. So, also a class 'F' insulating material will give a service life of about 20, 000 operating hours at its maximum possible temperature of 155 deg. C.

But, when you subject a class F material only to class B limits, it gives an extended service life of about 1, 00, 000 hours at an operating temperature of 130 deg.C.

Also, as standard service conditions cannot be guaranteed, the insulation service life of the motor increases even under the worst possible conditions of service - if a class F material is provided but its temperature rise is limited to that of Class B.