# Motor question



## fanelle (Nov 27, 2011)

all motors I have delt with are rated to work at 40 deg. Cel. ambient tempature. What they can see with an infaread gun and what the surface temp is will vary depending on what the ambiet temp. in the room and the load on the motor. If its hot the motor surface will be hot if its under heavy load the motor will have to disapate more heat across its surface. 

You can check your V/A/Hz curve to make sure its behaving in range but if its operating at full RPMS it should be fine. If the temp is still high you can always bolt on a power fan on the back.


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## Tom45acp (Sep 6, 2011)

That 40 C temp rise is 104 F above ambient, so you could easily be looking at a temperature of 170 to 180 F & that is plenty hot. One of my customers had a fan motor that ran pretty close to max temperature rise and it lasted for close to 15 years of use at 16 hours a day.

Just because the utility is within their tolerance, doesn't mean that all is well. Localized hot spots can shorten the life of the motor and if your voltage imbalance is more than 2 or 3% it could be a cause for concern.


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## micromind (Aug 11, 2007)

Most motors have maximum insulation temperatures listed as class A, B, F and H.


The maximum (this is the hottest spot of the windings inside the motor) temperatures are 

Class A = 221ºF

Class B = 266ºF

Class F = 311ºF

Class H = 356ºF

Most motors are class B, some are class F. 

As you can see, they can get pretty durn hot. Way too hot to touch.

If the motor is drawing nameplate current or less, and it's in 40ºC ambient or less, and airflow around it isn't restricted, it's fine no matter how hot it feels.


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## JRaef (Mar 23, 2009)

It's not that simple, but yet it CAN be simple if you have all of the data.

On the motor nameplate, there will be a code for the insulation temperature RISE rating. If for example it says "Class H Ins.", that means that the insulation is rated for operation with the termperature rising by 125 deg. C, which is 257 deg. F. Temperature RISE means ABOVE the ambient temperature, defined as 40C (104F) unless specifically stated otherwise. But that is an average, there are also allowable hot spots of +10C (if I remember correctly). So in theory if the pool house was already 104F, the temperature rise of the air coming out of the motor could be as high as 361F, and the hottest spot on the winding (not the outer shell) could theoretically be 411F.

Class A = 55C rise
Class B = 80C rise
Class F = 100C rise
Class H = 125C rise

So what does this mean?

It means...
A) you cannot tell him anything useful until you know what the nameplate on the motor says about the insulation rating first.
B) looking at the outer case of the motor with an IR gun does not tell you anything very useful anyway, because the temperature ratings are based on the INTERNAL winding insulation.

People buy their IR toys and shoot them at everything, not knowing what the heck they are looking at.


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## MDShunk (Jan 7, 2007)

Keep in mind the fact, also, that two motors with the exact same insulation will have "normal" temperatures that are wildly different. Take the otherwise same motor in TENV styles and ODP styles, and the TENV will seem very hot if put to the exact same duty as the ODP style motor. You need a bit of historical data on the motor to determine how hot is "too hot". You can still be within the operational limitations of the winding insulation and have a genuine problem with motor bearings or tightness of the driven load and have the motor be "too hot". I'm guessing you're doing some sort of PM checks and that's why you're asking. Until you start to get some historical data of a particular motor put to a particular use, you'll really have no idea if it's trending hotter and hotter. Very often, by the time you reach the maximum temperature the windings can handle, you've had a problem festering for quite some time.


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## maddhatterr (Sep 21, 2009)

Thank you very much for the help. I am returning there tomorrow to check how things are running for them before they open this friday. The voltage imbalance is only 1.26% but the motor only has a 1% imbalance tolerance. The motor should draw between 38 and 40 amps but is running A phase 42 amps, b phase 35 amps, and c phase 44 amps.(B phase is the high leg).

It is also a brand new motor(US Motor) driving a pump. It was supplied by a pool supply company through the plumber before I got involved.


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## IMM_Doctor (Mar 24, 2009)

If the pump inlet has a 90 degree butterfly valve with squeeze handle that engages into teeth, you can stop the valve from openeing to a full 90 degrees, just short at about 80 degrees, and many times put a bolt into holes provided. (So that future valve closing and re-opening stops are your designed postion).

Put your amp meter on the pump while adjusting this valve. By slight reducing the inlet head of water, you can drop the FLA to just below nameplate. Do not over do it and starve the pump. Just a small percentage usually does it.


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## JRaef (Mar 23, 2009)

maddhatterr said:


> Thank you very much for the help. I am returning there tomorrow to check how things are running for them before they open this friday. The voltage imbalance is only 1.26% but the motor only has a 1% imbalance tolerance. The motor should draw between 38 and 40 amps but is running A phase 42 amps, b phase 35 amps, and c phase 44 amps.(B phase is the high leg).
> 
> It is also a brand new motor(US Motor) driving a pump. It was supplied by a pool supply company through the plumber before I got involved.


Roll the conductors and see if the imbalance follows the conductors. If it does, it's not a motor problem. If it doesn't or the imbalance changes, it's something in the motor. There are slight differences in motor impedance that are natural, as well as slight differences in voltage from the line. Sometimes by rolling the conductors you can work them together to get a better current balance.


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