Electric Motor Service Factor Explained

Motor service factor sf is the percentage of overloading the motor can handle for short periods when operating normally within the correct voltage tolerances.

Electric motor service factor explained.

Motor service factor sf defined by nema this is practical as it gives you some fudge in estimating horsepower needs and actual running horsepower requirements. For example the standard sf for open drip proof odp motors is 1 15. This would imply a temperature increase ranging from 15 to 25 degrees celsius when compared to the nominal load which would translate into a decreased insulation life span. That s simple enough right.

A motor operating continuously at a service factor greater than 1 will have a reduced life expectancy compared to operating at at its rated nameplate horsepower. Service factor is an indicator of the amount of overload a motor can be expected to handle for example a motor with a 1 0 service factor cannot be expected to handle more than its nameplate hp on a continuous basis. A motor designed to operate at its nameplate power rating has a service factor of 1 0. The nema national electrical manufacturers association standard service factor for totally enclosed motors is 1 0.

Some applications require a motor that can exceed the rated power. For example you may find a 100 hp motor with a sf of 1 15 driving a 110 hp load under the incorrect assumption that it tolerates up to 115 hp. Service factor service factor sf is an indication of how much overload a motor can withstand when operating normally within the correct voltage tolerances. This means that the motor can operate at 100 of its rated power.

To most it seems quite simple. The service factor sf of an ac motor is a measure of continuous overload capacity at which a motor can operate without overload or damage provided the other design parameters such as rated voltage frequency and ambient temperature are within the manufacturers specifications. In these cases a motor with a service factor of 1 15 can be applied to the rated power. Nema service factor at synchronous speed rpm for drip proof motors.

If it is a 1 0 you can run a motor to 100 load if it is 1 15 then it can be loaded to 115 of its rated load. The service factor sf is commonly misunderstood as an allowable overload for electric motors. A sf is an operational margin. However motor operation under these conditions leads to many performance issues down the road.

Motor service factor sf is the percentage multiplier that a motor can handle for short periods of time when operating within its normal voltage and frequency tolerance. A motor with a 1 15 service factor can be expected to safely handle infrequent loads to 15 past it s. This means that a 10 hp motor with a 1 15 sf could provide 11 5 hp when required for short term use.