Electric Motor Service Factor

Likewise for each power and speed the mg 1 standard defines a frame number which is linked to the service factor.

Electric motor service factor. 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. The nema national electrical manufacturers association standard service factor for totally enclosed motors is 1 0. The rated horsepower of an ac motor to the rated armature current of a dc motor or. 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.

To most it seems quite simple. In the u s the defacto standard for ac motors is the nema standards. For example the maximum motor load for a 1hp electric motor with a service factor of 1 15 is. Most hazardous location motors are made with an sf of 1 0 but some specialized units are available for class i applications.

As per the standards a motor s nameplate should indicate the service factor as sf. To the rated output of a generator. 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. The canadian electrical code defines service factor as a multiplier that when applied to.

The standard which defines the service factor for motors and generators is the mg 1 standard which in turn defines powers and speeds. The reference point is a service factor of 1 which would mean a motor cannot operate over its rated horsepower or hp without overheating. Traditionally totally enclosed fan cooled tefc motors had an sf of 1 0 but most manufacturers now offer tefc motors with service factors of 1 15 the same as on odp motors. Motor service factor is probably the most misunderstood value on a motor nameplate.

Most motors have a duty factor of 1 15 for open motors and 1 0 for totally closed 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. Typical service factors sf for ac motors. Motors of 10 hp and up usually have a service factor of 1 15.

The service factor sf is a measure of periodically overload capacity at which a motor can operate without damage.