Motor temperature rise of class F insulation

Due to having found a 7.5 HP single phase motor, I swapped the three phase motor on my compressor for a single phase Marathon motor:

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What surprised me was that this 7.5 HP motor has insulation class F and, apparently, it would be normal to see a rise in temperature to

311 degrees F during continuous operation, at maximum ambient temperature of 105 degrees F. We rarely get 105 degrees around here, but 100 is normal for a summer, so the motor can get to way above the water's boiling temperature.

This seems hazardous to me, personally.

I did verify that the amp draw of this motor, with the compressor close to full pressure of 140 PSI, is about 30 amp, so the motor is functioning within its 30 amp nameplate amp draw. i

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Ought to be good for driving moisture out of the windings. I'd certainly consider it to be hazardous to not have at least a "Caution hot surface" label on it, or better yet a wire guard around it.

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Pete C.

The label only indicates that it has class F insulation. It doesn't indicate the design temperature rise. Class F insulation with class B temperature rise has been fairly standard for more than 30 years.

A motor that didn't have at least class F rated insulation would not be worth manufacturing these days.

Mark Rand RTFM

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Mark Rand


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Cydrome Leader

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