Cycle Duration Factor of Electric Motor?

Most likely this means if you want to run the motor continuously, you should not do so at more than 40% of its maximum load. If you run at more than this, you should do so only for short periods of time and allow it to cool before running it again. The length of the duty cycle (run time plus cool-down time) may be specified by the manufacturer, although it would be dependent on the ambient temperature of the motor.

If you are careful not to overheat the motor, and the load doesn't accelerate violently on start/stop, the life limitation would be determined by bearing or brush/commutator wear or metal fatigue in the windings (typically shows up as a broken wire).

The ratings you refer to are applicable to wound rotor motors (slipring motors), used on crane applications.

The 40% refer to the time the motor will be operated under full load conditions, 60% of the time the motor will operate under no load (or a fraction of the full load) conditions. The main hoist motor, for example will not always be under full load conditions, you may hoist an empty container or during lowering of a load gravity will assist the motor.

Standard motors are manufactured for 2 to 3 starts per hour (due to the high starting currents) Motor failures will occur if these motors are started 20 or 30 times per hour.This will obviously not work on a crane application to start the motor twice every hour.

You therefore need to specify the number of starts on these motors to your own requirements (normally 150 starts per hour)