Cyndi Nyberg
Former EASA Technical Support Specialist
Have you ever wondered why the shaft of an electric motor is often larger than that of the driven equipment? One reason for this is that the standard shaft sizes specified for the standard NEMA frame machines are larger than the minimum required, as we will see in the examples below. Manufacturers tend to design using an ample safety factor. Given the dire consequences if a shaft breaks, that is understandable.
Even so, the difference between a T and TS shaft can raise questions for those unfamiliar with mechanical design. It is important that the shaft is large enough to (a) transmit the required torque without exceeding the maximum allowable torsional shearing stress for the shaft material, and (b) prevent torsional deflection, or twisting, during service. All this, with a substantial safety factor.
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