Electric Motor Service Factor Explained

For example the standard sf for open drip proof odp motors is 1 15.

Electric motor service factor explained. 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. Some applications require a motor that can exceed the rated power. 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. 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.

The service factor sf is commonly misunderstood as an allowable overload for electric motors. A sf is an operational margin. 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. To most it seems quite simple.

This means that a 10 hp motor with a 1 15 sf could provide 11 5 hp when required for short term use. 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. In other words it is a fudge factor that give extra horsepower when it s occasionally needed.

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 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. A motor that operates with a service factor of 1 15 will have a greater temperature increase than if it had no service factor since it uses a higher current. Motor service factor sf is the percentage of overloading the motor can handle for short periods when operating normally within the correct voltage tolerances.

This means that the motor can operate at 100 of its rated power. That s simple enough right. A motor designed to operate at its nameplate power rating has a service factor of 1 0. A motor with a 1 15 service factor can be expected to safely handle infrequent loads to 15 past it s.

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. The nema national electrical manufacturers association standard service factor for totally enclosed motors is 1 0. 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.