Motor insulation classification

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duhhuh

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Does anyone have any information on motor insulation classifications and how to correctly interpret what the actual temp on a motor should be? (for example: a Class F [40 degree C Ambient-Continuous]

Should a 7.5 HP/3Ph motor, running at 8.8A/460V (FLA is 10.2)be operating at a temp of 98.6 degree C in an area with a 24.2 Ambient temp.?

Should any same size motors, same area, be running over 40 degree C? if yes, what is allowable/normal?

Thank you
 
Re: Motor insulation classification

There are four motor insulation classes: A, B, F, and H.

A: 105? C - 221? F
B: 130? C - 266? F
F: 155? C - 311? F
H: 180? C - 356? F

So based on that, it appears your motor is operating well within its temperatue class.
 
Re: Motor insulation classification

I'll try this I haven't figured out to well how to put in these links. Check out this article http://www.ecmweb.com/mag/electric_hot_issue_motor/, It explains the insulation class meaning fairly well. You have to look at the temperature rise of the motor. Another thing about motor's they get hot when they run, especially close to full load and if they are running into the service facto range of 1.15 they can get real hot. The thing to watch is trending. I don't have all the specific #'s for limits it all depends on the insulation class.

Your motor does sound a little warm, but if it has always been warm like that, then you need to just keep an eye on it. Thermography is great for these things, but still it is trending you need to watch for, just like in vibration analysis and any other predictive maintenance. You can't walk in and go oh that's out of spec and it is going to fail. Predictive maintenance is based on trends.

98 degree's C is close to 208 degree's F and yes that's warm. But I've known motors and things electrical that get even hotter.
 
Re: Motor insulation classification

GREETINGS TO ALL.

The inulation classes are as described above in that

Class A 105?C
Class B 130?C
Class F 155?C
Class H 180?C

The most common rating is Class F @ 155?C

To this we have to figure for a 10?C hot spot
Then Subtract 40?C for ambient temperature.

So the allowable temperature rise is then 105?C.

This should however be a maximum at full load and these temperatures are typically measured with Resistance temperature Detectors imbedded within the winding.

If the outside frame of the motor is exhibiting these values of temperature rise. One should check the amp draw and the voltage balance. As unbalanced voltages can induce negative sequence currents that will increase current draw and phase imbalance. A hot frame can also cause mechanical distortion of the frame which will increase vibration and overload bearings.

Hope this helps.
 
Re: Motor insulation classification

The temperature rise + the ambient + the hot spot allowance should not exceed the insulation class. The motor surface temperature should not exceed the insulation class minus the hot spot allowance. As brigadier_92 mentioned this leaves a rise of 105?C

A Class F (155?C), with a hot spot allowance of 10?C, could have a surface temperature of 145?C.

Based on your ambient of 24.2?C and surface temp of 98.6?C, you only have a temperature rise of only 67.4?C. Too hot to touch but not extreme.
 
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