Insulation Class F/B

NEMA Insulation Classes

Check the Sieman's web site?

Most likely the motor was designed to class F standards as a minimum standard by the manufacturer...meaning it is designed to operate in either F or B standard...

This means that the motor is so designed that its temperature will not exceed class B limit i.e. 130 degree, although the class of insulation for the winding is selected as F. Thus adequate margin (25 degree) will be provided for temperature rise and the expected life of motor insulation will be more as compared to another motor of same rating but with insulation class B.

it is a class F motor with temperature limit of 155 degree. Temperature rise according to B. So 155-80=75. The motor can be use in a place that the teperature no more than 75 degree.

Can you please explain what is 80 degree and what is meant by " The motor can be use in a place that the temperature no more than 75 degree " ?

Most likely, the answer is, insulation of the motor is designed to class F and temperature rise of the motor is restricted to class B under rated voltage, frequency, and full load condition. That is to say there is a temperature buffer of 25 degree celcius( 155C- 130C). The cooling system of the motor is designed to achieve the above.

Manindra

Yes, you are right.

Motor has class F insulation with temperature rise limited to class B. That is to say, though the insulation of the motor windings have been designed as per class F motor, under normal running conditions, the winding temperature shall not exceed class B. However in this regard, the duty of the motor has also to be considered. If the motor is designed for S1 duty is not recommended to use it for S4 duty.

Along with duty type S1, S4 etc. you should also mention cyclic duration factor (CDF) and duty cycle which has direct influence on temperature rise of the motor. S1 duty motor can very well be used for S4 duty if the rest and de-energised time of the motor is more.

sorry debata, I thought that much is pretty well understandable and so didnt be specific But I am glad u got my point

S1duty motor may be used for S4 duty with reduced KW rating in exceptional/ under compelling situation. The reduced rating should be carefully considered.

Manindra

Insulation Class B allows temperature rise 130C and class F allows 155C.

Dear Mr. coolyar,

It indicates that the Motor is designed for Insulation Class F, but the Temp. Rise is (or will be) restricted to Insulation Class B.

DHAYANANDHAN.S