Electric Motor Service Factor

Motor service factor is probably the most misunderstood value on a motor nameplate.

Electric motor service factor.

The rated horsepower of an ac motor to the rated armature current of a dc motor or. Motors of 10 hp and up usually have a service factor of 1 15. Typical service factors sf for ac motors. In the u s the defacto standard for ac motors is the nema standards.

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. As per the standards a motor s nameplate should indicate the service factor as sf. The standard which defines the service factor for motors and generators is the mg 1 standard which in turn defines powers and speeds. For example the maximum motor load for a 1hp electric motor with a service factor of 1 15 is.

Likewise for each power and speed the mg 1 standard defines a frame number which is linked to the service factor. A motor operating continuously at any service factor greater than 1 will have a reduced life expectancy compared. 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. 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 a measure of periodically overload capacity at which a motor can operate without damage. 1 15 x 1 1 15hp anything above this load will certainly result in motor overheating and consequent damage of the ac motor. To most it seems quite simple. Most hazardous location motors are made with an sf of 1 0 but some specialized units are available for class i applications.

The reference point is a service factor of 1 which would mean a motor cannot operate over its rated horsepower or hp without overheating. A service factor or sf is a factor representing the capacity at which a motor can operate without overloading or damaging its core or components. The service factor sf is commonly misunderstood as an allowable overload for electric motors 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. Most motors have a duty factor of 1 15 for open motors and 1 0 for totally closed motors.

To the rated output of a generator.