By Mike Howell
EASA Technical Support Specialist
Too often, replacement specifications for three-phase squirrel-cage induction motors cover only basic nameplate data such as power, speed, voltage, and frame size, while overlooking other important performance characteristics such as the design letter. This can lead to misapplication of a motor, causing poor performance, inoperability, or failures that result in unnecessary downtime. To avoid these problems, familiarize yourself with the following speed-torque characteristics and typical applications for design letters that NEMA and IEC commonly use for small and medium machines (up to about several hundred kilowatts/horsepower).
- NEMA Designs A and B, IEC Design N
- NEMA Design C, IEC Design H
- NEMA Design D
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ANSI/EASA AR100
More information on this topic can be found in ANSI/EASA AR100
EASA Technical Manual
More information on this topic can be found in EASA's Technical Manual- Section 1: Machine Identification & Bearing Information
- Section 2: AC Machines
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