Duty Cycle Explained

What it is

A duty cycle rating is always paired with an output. For example, "200 A at 60% duty cycle" means the machine can weld at 200 amps for 6 minutes out of every 10, then needs 4 minutes to cool. IEC 60974-1 and NEMA EW 1 both base duty cycle on a 10-minute period. IEC 60974-1 tests at an ambient temperature of 40°C. At lower output, the same machine can run a higher duty cycle; at higher output, the duty cycle drops.

How to read it

Find the rated output line on the nameplate or in the manual. It lists amps, volts and duty cycle together, often at two or three points (such as 60% and 100%). Many manuals include a duty cycle chart showing output across the full range. Use the chart for the setting you plan to run.

Duty cycle in a 10-minute period

Values are calculated directly from the 10-minute period.

Key points

• Compare machines at the same output and the same standard. A 60% rating at 200 A is a higher rating than 60% at 150 A.
• Ratings tested at 40°C ambient reflect hot shop conditions. Some older or low-cost ratings use cooler test conditions, which makes them look better.
• When the duty cycle is passed, a thermal switch usually shuts off output until the machine cools. Repeated overheating shortens component life.
• Torches and guns have their own duty cycle ratings, separate from the power source. Check both.
• Real work includes setup, fit-up and changing rods, so actual arc time is often well below the rated duty cycle. Production lines with long welds need a higher rating.
• See welding power sources for machine types.

Common mistakes

• Reading duty cycle as a percentage of an hour.
• Comparing ratings at different outputs or test temperatures.
• Ignoring the gun or torch duty cycle on high-output jobs.
• Blocking the machine's air vents, which reduces real duty cycle.

Governing standards: IEC 60974-1 (arc welding power sources, including duty cycle test conditions); NEMA EW 1.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.