Service factor 2

[vk1975]

Hi All

If a motor is designed for a service factor of 1.15, can we run motor at these loads continuously
Can anybody clarify this

 

[DRWeig]

The answer depends on conditions. Here's a good discussion:

http://findarticles.com/p/articles/mi_m0BPR/is_4_17/ai_62370062/

Good on ya,

Goober Dave

 

[petronila]

Hello vk

The most important is how long the motor will run, the overload percent is not continous rated so if you run the motor continous under this conditions the life will be very short.(Really will be a permanent overload and the motor most overheat and insulation will be deteriorated.


Example: You need a 10 HP motor, then you buy a 10 Hp motor and if the motor has a 1.15 S.F mind if you have an overload the motor could support saftely and shortly a 15 % of overload this is a security factor to allow the motor produce 11.5 HP but not longer, but if the motor Runs all the time in that conditions minds you have a design problem becuse you need really a 11.5 HP and not 10 HP motor.

Regards

Carlos

 

[jraef]

Officially, the NEMA MG-1 definition of Service Factor used to include words to the effect of "limited time", but it changed to eliminate that because there was no definition of oit agreement on the amount of time. Now all it says is something more ambiguous and non-committal like 'motor torque, power factor and voltage tolerance may not be as designed and motor life may be expected to be lower' (I'm posting from my iPad so I don't have my copy of MG-1 with me).

So the answer really is what the previous posters said, it depends, but don't expect it to be the same as buying a properly sized motor in any case. OEMs and design-build contractors tend to be the ones who use this, because they tend to only be concerned with the motor lasting out the warranty, which it likely will, and not being any larger (costing more) than absolutely necessary. If you do this as an end user, all you are doing is passing the problem onto your future self, or your successor.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[dpc]

You can run it continuously right up until it fails. Expect a shorter life if run at service factor load long term.

 

[MiketheEngineer]

Bottom line - when this motor blows - buy a bigger one!!

 

[jraef]

I was able to read the official wording from NEMA MG-1 but cannot copy it directly. However what I said is essentially the way it is worded excpt it says efficiency, power factor and speed will be affected, not torque and voltage tolerance. It also goes on to say it will have a reduced life expectancy compared to a properly selected motor, without qualification or quantification. They also add another paragraph that says, to the effect:

If you want continuous overload capability, it is recommended that you use the next size up to avoid damaging the motor's insulation and to ensure providing necessary torque.

Take it for what it's worth.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[electricpete]

should be a faq

=====================================
(2B)+(2B)' ?

 

[petronila]

Hello

Adding to all inputs, I like to highlight is not a good practice the continuos motor operation in Service Factor condition exceeding the rated load, due to some motors may not supply correct starting and pull-out torques and also experiment incorrect starter/overload protection operation.

Regards

Carlos