Fractional horsepower motor
A fractional horsepower motor (FHP) is an electric motor with a rated output power of 746 Watts or less. There is no defined minimum output, however, it is generally accepted that a motor with a frame size of less than 35mm square can be referred to as a 'micro-motor'.
The term 'fractional' indicates that the motor often has a power rating smaller than one horsepower.
Fractional horsepower electric motors are exempt from the US Energy Policy Act of 2005 and the new EN 60034-30:2009 [1] ruling of European directive 2005/32/EC [2] concerning the efficiency classes of low-voltage three-phase asynchronous motors.
The earliest commercially successful electric motors date back to the latter part of the 19th century when Nikola Tesla patented his induction motor in 1888. The development of fractional horsepower motors however would not have taken place without the push toward urban, and later rural, electrification, using alternating current. Electrification began in cities around 1915 and with electrification so too came the potential market for washing machines, refrigerators, vacuum cleaners and a host of other commercial appliances. This was recognised by major manufacturers, like Westinghouse and General Electric, who were already in the business of manufacturing large motors for industrial installations. By 1920, over 500,000 fractional horse-power motors were powering washers and other appliances in America.
After the second world war the demand for FHP motors grew, particularly throughout the consumerist boom of the 1950s and 60's. Today the European FHP market is worth an estimated $4.5 billion with some 300 million units in manufacture.
Servo motors and stepper motors are specialist types of fractional horsepower electric motors usually intended for high-precision or robotics applications. Usually running from a DC supply, when combined with a planetary gearbox can offer accuracies less than 8 arc-minutes (2/15ths of a degree, or approx. 2.3 milliradians). Due to their specialized nature, however, these types of motors tend to be expensive compared with standard, or general purpose, lower-precision units.
...
Wikipedia