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Much has been written about motors on variable-speed drives, high-speed rigid shaft motors, impact of API Standard 541, motor diagnostics, etc. Most of these papers and articles assume that the reader has significant knowledge of motor theory and operation. However, this assumption is overly optimistic, considering that only a few colleges teach motor theory today, and that application experience at motor user locations has been reduced in recent years. This paper is the third in a series of papers where the authors provide answers to questions that are routinely asked by working engineers in industry. The authors present motor theory and application information with an extensive reference list that will help working engineers increase their general understanding and knowledge of motors. This series of papers also serves as a valuable reference for those who apply and specify motors.