Duty cycle is used to determine the actual work that the power system of a resistance welder is performing. Machines by design are not meant to exceed 50% duty cycle. The cables, shunts, transformer, controls and all conductors are designed with this value. If exceeded the life of the machine components will be shortened dramatically.
Knowing at what level you operate at is important in setting your weld schedules. The formula shown below is based upon standard AC - 60 cycle welding with a one minute integration time period.
For additional information see:
Reference: RWMA – Resistance Welding Manual Section 19.3