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Arc welders, a common type of electric welder, typically do not operate continuously. Even if they are in use most of the time, there tends to be a cyclingCyclingEven a robotic welder will weld a seam or joint, move to another joint and then weld again, and so the welder's circuit is not constantly loaded. that takes place between work pieces or between welds.
Because of this duty cycle, the ratings of the conductors to welders may sometimes be reduced from the actual nameplate value of the welder by applying a multiplier (a percentage factor) from Section 630.11.
On the other hand, it is necessary to account for inrush current, which happens every time the welder is started. So the method of sizing a conductor provides an estimate of the overall heating effect that occurs when conductors are not loaded continuously.
Resistance welders also have a duty cycle in use, but the duty cycle is usually a lower number and the multipliers are different.
© Hughes Associates,Inc. 2012