Over sizing the breaker question?

[performance]

I hate to disagree, but No, normal rules are not applied. I've discussed this not only with electrical engineers, but also with 40 year industrial electricians. There is a reduction for duty cycle limited machines, and a formula that they use that is different than the standard for appliances. And I believe a different requirement for breakers. Again, Section 630 discusses this in detail. If your inspectors didn't know this, then they weren't on top of their game, as it is spelled out in black and white. Run length is considered, of course, but different gauges are allowed according to maximum duty cycle. In my research, I even found a dedicated class offered for wiring welders and similar components.

[ASE_MasterTech]

I hate to disagree, but No, normal rules are not applied. I've discussed this not only with electrical engineers, but also with 40 year industrial electricians. There is a reduction for duty cycle limited machines, and a formula that they use that is different than the standard for appliances. And I believe a different requirement for breakers. Again, Section 630 discusses this in detail. If your inspectors didn't know this, then they weren't on top of their game, as it is spelled out in black and white. Run length is considered, of course, but different gauges are allowed according to maximum duty cycle. In my research, I even found a dedicated class offered for wiring welders and similar components.

Perhaps I wasn't clear, so again I will state;
Appliance considerations are not part of 'hard wiring' regarding wire gauge vs breaker/fuse sizing, rather it is the other way around.
You wouldn't/shouldn't ever put a 50amp device on a 40amp circuit (regardless of 'duty cycle'), but you may put a 40amp device on a 50amp circuit
BTW, good luck explaining the under-gauged wire 'duty cycle' thing to a fire inspector sent out by your Homeowners Insurance company.
I'm just sayin...

[performance]

Nothing to explain. I'd just point them to section 630.

[performance]

There is also a lot written about it on the web. Its not to say a wire can't be oversized. Breaker size is regulated though, I believe to no more than 200% if I remember right.

However, a sharp welding inspector would recognize a proper welding receptacle such as a NEMA 6-30 and know its purpose.