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'.
Fractional horsepower electric motors are exempt from the US Energy Policy Act of 2005 and the new EN 60034-30:2009  ruling of European directive 2005/32/EC  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). Due to their specialist nature however these types of motor tend to be expensive compared with standard, or general purpose, lower-precision units.
Fractional horsepower motors are used across a wide range of industries and applications for a variety of motion and compression needs. The largest portion of sales can be attributed to the automotive sector however, accounting for some 35% of all FHP motor sales, driving auxiliary applications such as electric windows, wind shield wipers, powered seats and wing mirrors, central locking systems and roof and trunk openers. In Europe the majority of these applications are fulfilled by the industry's largest players: Brose (formerly Siemens), Bosch and Nidec (formerly Valeo).
The second largest area of consumption is the field of white goods and small domestic appliances (approximately 12% of the European market). With FHP motors being used to drive pumps and compressors in refrigerators, coffee machines, washing machines etc. provide suction in vacuum cleaners and a variety of other switching and motion tasks across the ever increasing variety of domestic products. Until the recent divestment of its motors interests Electrolux was believed to be Europe's largest manufacturer of FHP motors for domestic appliance applications.
Industrial applications consume a similar number of units to that of domestic products with FHP motors being used across a variety of conveyance and process applications.
Other applications include: pumps & compressors; medical devices; portable tools; office machinery; HVAC
Many major international diversified engineering firms now possess a fractional horsepower manufacturing capability, such as Siemens and Bosch, and while there are many other Industrial Automation firms who also make fractional products, these are often a non-core offer. There are however a number of dedicated specialist FHP manufacturers still in existence:
Groschopp - based in Sioux Center, Iowa, Groschopp offers energy efficient motors, gearmotors, gearboxes reducers, AC, DC, Brushless DC Motors, Universal Motors and controllers
Baldor Electric Company - based in Fort Smith, Arkansas, Baldor Electric offers AC and DC motors and controllers
- Raymond McInnis, A history of the amateur woodworking movement; Appendix 21 http://www.woodworkinghistory.com/appendix_21.htm
- E T Painton Small Electric Motors DC and AC London: Pitman, 1923
- George A Schock, Early History of Baldor Electric Co, 1920-1976. Fort Smith, Arkansas: Baldor Electric Co, 1992
- Frost and Sullivan, European Fractional Horse Power Motors Market, 17 March 2000
- Plimsoll Portfolio Analysis, second edition 2008
- CEMEP: Comité Européen de Constructeurs de Machines Electriques et d'Electronique de Puissance
- European Union electrical equipment directives
- NEMA: National Electrical Manufacturers Association (USA)
- IEC: International Electrotechnical Commission
- REMA: Rotating Electrical Machines Association
- Whitepaper – Efficiency in Fractional HP Motors & Gearmotors