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A fractional horsepower motor is one which produces less than 746 watts during operation; it is a motor whose total output does not quite meet the 1 horsepower standard. It is so named because an engine producing so little power cannot be rated by the conventional horsepower scheme. There is no minimum power rating to be considered a fractional horsepower motor; because of this, it is the bottom floor in power ratings, with no real classification beneath it. A substantial advantage to running a fractional horsepower motor is that it is exempt from some laws which govern more powerful motors, such as the United States Energy Power Act of 2005, along with similar directives in the European Union.
The primary use for fractional horsepower motors is powering small electronic and consumer devices such as vacuum cleaners, refrigerators, and washing machines. Additionally, these motors are seen in auxiliary devices on cars, such as in electric windows, power seats, moon and sunroofs, and windshield wipers; roughly 35% of all fractional horsepower motor sales can be attributed to automobiles. Such motors make the devices they power wholly independent of the actual engine in the motor vehicle; even if the primary engine in the car stops running, the fractional horsepower motors in the vehicle can still function, so long as the car still has a working electrical system.
Alongside their use in general consumer goods, fractional horsepower motors are used in business and commercial applications for jobs which require a high degree of precision. A fractional horsepower motor does not produce as much vibration as conventional high-powered motors. This allows for more controlled use in high-precision tasks.
Stepper and servo motors are the specific types of fractional horsepower motors used in these instances; both are specialist motors that allow for a sensitive level of inputs. Due to their sensitive nature and high degree of accuracy — when paired with a planetary gearbox, these types of motors can be accurate up to 2/15ths of a degree — stepper and servo motors often come at a price premium over the conventional fractional horsepower motors seen in most consumer goods. Due to this, their use is limited to more exclusive fields. Robotics is one of the primary ways in which these high-quality types of motors are used.
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