Decades ago, when the electric motor industry was still in its infancy, a game of “one-upsmanship” played out between the various motor manufacturers. That is, one manufacturer would make its motor slightly more powerful than competitors’ motors of the same rating. In response, a competitor would increase the power of its motor, and so forth. It eventually became very difficult to compare motors from different manufacturers, and in time, standards were established and became known as service factor. Today, the National Electrical Manufacturers Association (NEMA) specifies service factors for electric motors, and different horsepower ratings carry different service factors. Continue reading
This is a question we regularly receive on the Hotline. Understanding how the service factor affects an electric motor can be confusing, but it is not as complicated as it may seem. This issue of the Franklin AID explains the term service factor and its relationship to AC submersible motors.
The National Electrical Manufacturers Association (NEMA) defines service factor in section MG1 – 1.43 of their manual as: “The service factor of an alternating current (AC) motor is a multiplier which, when applied to the rated horsepower, indicates a permissible horsepower loading which may be carried under the conditions specified for the service factor.” The conditions under which service factor may be applied are described in NEMA MG1 – 14.36 as: “When the voltage and frequency are maintained at the value specified on the motor’s nameplate, the motor may be overloaded up to the horsepower obtained by multiplying the rated horsepower by the service factor shown on the nameplate.” Continue reading