AC motor nameplate markings vs Actual test

The "official" definition of Service Factor is NEMA publications says something to the effect that SF is an amount of additional output power the motor can deliver for a short time (not defined), but at which other stated performance date will not be accurate. it also goes on to say that expected motor life will be diminished.

But those are guidelines, there is no hard and fast rule for what that 1.15SF really means, othr than the fact that if the motor is run in the SF, the amps will be higher. So every motor design will be different, but it's a given that you will increase the motor winding temperature. The one real rule is that for every 10 deg. C you raise the motor winding temperature above its rating, you cut the expected motor life in half. So if for instance your motor has a winding insulation temperature rating of 155C, and because you run it into the SF continuously, the windings get to 165C, you have shortened the motor life to 1/2 of what it should have been.