electric motor is running way to hot on dust collector.

[timholt]

There is a date plate on the motor with absolutely no marking on it.
I believe this to be about a 10 hp dust collector with a
leeson motor. the motor pulls about 33 amps which is about
right for a 10 hp motor ,but it's running about 195 to 200 degrees surface temp. the motor was rewound prior to us receiving it, all the wiring seams to be in good shape, wired
for low voltage 208v 1-7,2-8,3-9, 4-5-6 tied together. It has
a Square D starter with b-56 Heaters The heaters are running
about 115 degrees surface temp. I really think this is plenty of motor for this dust collector. I also put a plastic bag over one of the breather bags to drop the amps down some, this dropped the amps down 5 amps when I done this, I this would drop the motor load down enough to drop the surface motor temp
down to where the motor was in a good operating range.

Dropping the load didn't work. I think it's in the windings
what do you think # 8 wire run to and from the the starter
on a 40 amp breaker.

 

[jraef]

If the motor current is within the normal range, I would not worry about the surface temperature on the motor. Most newer motors (last 10 years or so) have at least Class B insulation which is rated at 130 deg. C (266F), many are even now Class F which is 155C (311F). In addition, if it is a Leeson motor it likely has a 1.15 Service Factor, which means it can theoretically run at over FLA for a while. The only problem I see on this motor at the moment is that you don't really know what the normal FLA rating is. But I would suspect it is 10HP also, because a 7.5HP would be significantly lower even if you were running into the Service Factor, and a 15HP would not likely be drawing that little and still be that warm.

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[aolalde]

Try to measure the shaft speed and calculate the slip (s).
s = (RPMsynch - RPMshaft)/RPMsynch
If the calculated slip is larger than 0.03 the magnetic field is too weak, the motor could be designed to operate at 230 volts and the actual voltage is only 208 or less, working on high slip and overheating. Not only the winding insulation but the lubrication and bearings could be on marginal conditions.
You could attempt to get the wining temperature ( in centidegrees) by the winding resistance change.
Measure the winding resistance (R1) while the motor is cold ( ambient temperature Ta °C), then after the motor has been running for several hours at full load, stop and measure imediatly (around 1 minute) the winding resistance R2.
The operating temperature T2 = R2/R1*(234.5+Ta) - 234.5

That temperature should not exceed 120°C for class B insulation or 145°C for class F insulation.

 

[dpc]

What jraef said. A Class F motor has an allowable insulation temp of 155 Celsius (hot spot). That's pretty hot.

If the motor is running at FLA in a warm ambient, the motor will be so hot you can't put your hand on it.

The other consideration is the ambient temperature. NEMA ratings are based on a maximum ambient of 40 C. Above that, the motor must be de-rated.

 

[ScottyUK]

Small lesson for Tim Holt and the rest of us: state your units when quoting measurements. I think Tim is using [°] F because he's also quoting power in HP, and thus is probably in North America, but I am having to guess. The rest of us are thinking in [°] C because those are our native units. If the numbers in Tim's original post are [°] C then his motor is in trouble even if it is a Class H machine.

----------------------------------

Sometimes I only open my mouth to swap feet...

 

[MotoDrv]

That is quite true. The temp UOM needs to be identified.
Now, at 208V the motor might be rated 230V able to be run down to 208V but at 208V the voltage might be dipping to a point beyond the motor's ability to operate properly due to over saturation of the rotor...(see aolalde's response)
If the original UOM was C, even at class H insulation, you are going to have a motor failure sooner than later