Unlikely to matter, I doubt any municipality has adopted the 2011 NEC yet and the vast majority of 2005, 2008 and 2011 hasn't changed.
FWIW, a 20% or less duty cycle allows an arc welder to be supplied based on 0.45 multiplier to the plate rating. So if the welder is rated 45A that means you only need to size the branch for 21A and can use a breaker sized at 200% of the conductor rating. Just don't exceed 2 minutes of use every 10. Even at 50% duty you can use a 0.71 multiplier and use a 30A sized branch.
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