What is meant by duty cycle in motor selection?

• A. The ratio of running time to total cycle
• B. The maximum rpm
• C. The ratio of running time to total cycle, used to determine how hard a motor will be worked over time
• D. The thermal rating of insulation

Answer: (C)

Duty cycle describes how long a motor runs under load in a repeating cycle and how that affects heating. It is the ratio of running time to the total cycle, and this ratio is used to estimate how hard the motor will be worked over time because it indicates how long heat has to be dissipated in each cycle. For example, a motor with a 60% duty cycle on a 10-minute cycle can run for 6 minutes and rest for 4 minutes. This helps determine whether the motor can run continuously, or only intermittently at a given load, without overheating. This concept is different from maximum RPM, which is a speed specification, and from the insulation’s thermal rating, which relates to temperature tolerance rather than how long the motor can be operated under load.