Maximum Allowable Temperature Rise for class F Insulation?

115C is specified in NEMA MG-1 as the maximum temperature rise for a continuous duty motor with service factor 1.15 or higher, in a 40C ambient.   You might roughly interpret this to indicate that the insulation temperature limit is 115+40 = 155C at the service factor load.   

It's not quite that simple/exact.  For lower service factor, the max rise would be 110C  at full load.  Also the associated temperature measurement is generally considered an average temperature if temperature is measured by resistance..... the hottest spot of the insulation is somewhat higher.  RTD can get closer to the hottest spot measurement.  The point I'm trying to make is there are a lot of different cases covered by the standard. 

 

 

 

Its seems this is truly one of the cases mentioned. Thank you.

At the place where I work, it is a bit hotter than other places. For this reason, the ambient is not 40 C, as an exception. Orders are supplied with 50 C modification to the default standard paragraph.

Regards- Ali M. Al-Shurafa 

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