I can’t offer any specific source or authority but it is commonly accepted that belt drives that are properly aligned and tensioned and that operate continuously last longer than belts that are subjected to the stress and strain of stopping and starting. Motors with Variable Frequency Drives also extend belt life due to the soft starting of the motors thereby decreasing the strain on the belts. Mechanical Engineering Design, Joseph Shigley, McGraw-Hill, 1977, mentions that a belt subjected to frequent starting and stopping must be selected with an overload service factor included. It is presumed that a belt not subjected to the starting and stopping would not require the overload service factor.
