Questions On Electric Motor With Answers

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When specifying a motor for a manufacturer, there are five key things you need to know first to identify the correct machine for your application.

This is an example of a motor nameplate where all the rating definitions are typically labelled. The first key thing you should know is power, measured in either horsepower for NEMA standardized machines, or kilowatts typically for IEC standardized machines.

Horsepower (HP) measures the amount of power a motor can give defined by torque multiplied by speed divided by 5250 feet pounds.

Number two is the rotational speed of the motor measured in time as rotations per minute (RPM).

These RPM ratings are typical speed requirements for industrial low voltage applications.

Number three is the electrical pressure measured in Volts.

The low voltage ratings highlighted in blue are typical for NEMA 60 Hz applications.

Number four is the frame size…

Frame sizes are dependent upon the power generated and may also be defined by the rotational speed and electrical pressure needed for the application.

Number five is the enclosure type.

Motors are used in a wide variety of indoor and outdoor applications requiring varying levels of protection from its environment. Several different cooling methods are employed to transfer heat away from it’s core and bearings. Typical low voltage enclosure types are open drip proof, totally enclosed fan cooled, and weather protected.

Knowing these first five things is a great start! There are many other application considerations such as orientation, torque, bearings, variable speed operation, etc. that will round out the ideal motor for your needs. I will publish more on these subjects in future articles.

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