Service Factor of Motors

You don't have to, the nameplate is your validation as long as you operate within its parameters.

What's the matter; don't you trust anything?

I suppose you could load a motor at FLA x SF for say 1000 hours and see if it fries or not.

NEMA MG1 ch.14.37.1 states:

"When the motor is operated at any service factor greater than 1, it may have efficiency, power factor, and speed different from those at rated load, but the locked-rotor torque and current and breakdown torque will remain unchanged.

A motor operating continuously at any service factor greater than 1 will have a reduced life expectancy compared to operating at its nameplate horsepower. Insulation life and bearing life are reduced by the service factor load".

IEC 60034-1 states "duty" instead of "service factor"-there are 10 duty types from continuous running, short-time, intermittent periodic and so on, and the "duty" maximum equivalent load is the continuous load [rated]-overload is forbidden, I guess.

Don't confuse people.

Service Factor & Duty are two different things. Even a motor whose duty is S1 can have a service factor of either 1 or 1.1 or 1.15 or 1.2.

Read the nameplate. Don't waste you time. _{(And ours)}

overload it and see

Sorry electricalexpert65, I don't see any reference to the "service factor" in IEC60034-1 [except for S10 where the maximum-not average-it is limited to 1.15 of S1 [continuous load]. However, I was wrong admitting the "duty" instead of "service factor" since are not similar definitions.

NEMA MG-1 is referring to "duty" indeed, but only as Continuous Rating and Short-Time Rating. (ch.1.40).

Load the motor as per the name plate SF for few minutes and find the temperature rise of the motor; the temperature should not exceed above the insulation class of the motor.

why do you need to re-validate what is already stated?

Here is link to give inf. required by you:-

http://electrical-engineering-portal.com/motor-service-factor-sf-defined-by-nema