The 30 amp breaker is the "fusible switch", no additional required. Article 630 in the NEC permits electric welders to be on circuits with apparently undersized wire (tables in the Article show the sizes) in cases where the duty cycle is below 100%. Your welder might be only 20%. Some of the imports are only 6%. 20% means what one can weld 2 minutes out of very 10 and the welder is permitted to cool for the other 8 minutes. The conductors also cool during that time. I would use #12 for the application. #10 would be better but not necessary.

"Article 630 in the NEC permits electric welders to be on circuits with apparently undersized wire"

Welding equipment, induction motors, and hermetic compressors are have there own code sections.

The wires are not undersized, but based on the characteristics of the equipment.

This equipment contains built in thermal overload protection, so all the breaker is doing is protecting the feeder against short circuits.

The low duty cycle of many welders allows plenty of time for the wires to cool off.

General purpose circuits (15 and 20 amp, 120 V) feeding multiple loads and used many times in every installation are designed with extra margin (#14 wire at 15 amps, #12 at 20 amps) to ensure safety.

Hey Guys. Sounds like I now know what I need to know. Thanks for the help!