Motor temperature

What is considered to be the normal operating temperature of a 3 phase induction motor?

40*C is considered ******t temp for most electric motors.

thank you.

You have to read the data sheet for each motor (or each model).

Some motors are designed to run much hotter in normal operation than others.

I assume that word is a m bient.

a m bient is not operating temp, its is the temperature in the environment.
http://en.wikipedia.org/wiki/******t_temperature
When you get to wikipedia just search it.

The data sheet should offer operating temp, not sure why a m bient was mentioned.

OK Phil, a m bient is a necessary word here, gotta release it.

I was always taught the five second rule. If you can keep your hand on it for 5 seconds then it is fine.

I read an article awhile back that completly dismisses that old rule of thumb. Some motors are designed to run hotter than others was the jist of it. Best to talk to the motor manufacturer.

40 C is pretty dang warm ie about 104 F (if I did my unit analysis right). Would not provide much cooling for a motor. I was taught the 5 second rule also in the Navy - the one exception to that was for the condensate pumps and HP brine pump motors. These were all variable freq drive (circa 1960 design). So far it has worked pretty well. Of course nowadays with insulation temperature ratings higher the motors will run warmer, but it is a good thrumbrule still. If the motor is hotter then check the nameplate and check with mfr.

Dan Bentler

40C is the normal summer temperature here in Perth WA (but it is dry heat )

Now, my question, does anyone know why the word ******t keeps getting censored?

a-m-b-i-e-n-t

Apparently a-m-bi-e-n is a recreational drug
Regards Alan Case

I think that feeling the surface temperature is not a good way to guess if a motor is OK or not.

Motors are rated in insulation "classes", which defines the max windings temperature. Class B = 130 degr.C for example.
Some motors have sensors in the windings so you can actually know the winding temperature.

Of course motors can operate at higher a_m_bient temperatures than 40 degr.C. Only you may have to derate the power that the motor can deliver.

Here is a good link that explains the whole thing:
http://www.motorsanddrives.com/cowern/motorterms4.html
quote from the link:
"motor surface temperature in modern motors can be high enough to be very uncomfortable to the touch. Surface temperatures of 75° to 95° C can be found on T frame motor designs. These temperatures do not necessarily indicate overload or impending motor failure."

Motor operating temperature is determined by the insulation rating. In North America, that would be Class A,B,F, and H. Class A is not considered a commercial/industrial rating so we have B,F, and H.

The temperature of the air around the motor plus the "degrees of rise" in the motor are added to get to the insulation's maximum temperature.

Class B is rated to 85 degrees C, F is 110, and H is 135.

So, for example, a motor has Class F insulation. If the environment is at 30 degrees C, the motor can rise 80 degrees C more to reach its rated temperature of 110. On the other hand, if the environment is at 50 degrees C, only 60 degrees of rise is allowed to reach a total of 110. Motors are normally rated at 40 degrees C for other reasons as well, such as bearing grease viscosity and grease life so running over 50 is not a good idea. Class H motors are usually only found around blast furnaces, heat treat ovens, and sometimes in TENV Inverter Duty motors.

As for that five second rule with your hand on the motor---just forget it! Considering that your skin starts to blister at 65 degrees C, even a Class B motor can fry an egg on its skin and be OK thermally.

Good one DickDV
I sometimes get called out for an "overheated motor", usually in the summer.
I have even seen maintenance guys hosing perfectly good motors to keep them from "overheating".
When I check amprerage and temperature and show them the name plate info they often think I'm wrong.

DickDV,
where do you get those numbers from ?

All references I can find state class B is 130 degr.C absolute, and class F is 155 degr.C absolute.
In the link I posted there is an example with a 'normal' class F motor with 1.15 service factor, and this motor may rise 115 degrees at 40 degr. amb.
The other motor types are allowed at least 105 degr. rise at 40 degr. amb.

I also know from practice that 'typical' class B motors with winding sensors specify the alarm level to be 130 degr.C.

Does a rise in motor temperature cause a rise in motor current and by what factor? I was told the same is true for VFD, that if the VFD get hot from a poorly ventilated panel, the motor current goes up as well. Is this true?

My information shows both.

http://www.iprocessmart.com/leeson/leeson_motor_temperature_article.htm

http://www.pump-zone.com/articles/388.pdf

I know there are standards but not sure I have them, will have to do some digging.