I am not sure about power from different circuits and the one clause that coult trip this up is that all the permanent wire would need to be 20A as part of the circuit. There is only 1 place they allow it and it is a short whip to a light fixture in a camper. But,,, and it aint,,, I understand that but it would certainly be similar to a fixture wire or a control wire with a dedicated use and no opportunity to have other loads applied. In fact this in a piped system would from a technical standpoint be about as good as it gets. This would be low on the list of code violations if there was one.
I only say this as a personal matter, not claiming it meets anything but would have done it without even thinking about it.
In theory could have used a wire just large enough to meet short circuit interruption for 20A. But if this was a light circuit, modern fixtures a 15A breaker would likely be well sufficient.
In my own shop I have several circuits and almost all individual piece,,,, no rows of similar stuff, lights in a given area may overlap and or come from different circuits. I have a couple 500 on stands but the fixed stuff is all 14 wire with a couple amps with the exceptinon again of 3 or 4 in paint booth. All that **** is cord and plugged to a 12/20 outlet.
I have half a dozen 4x4 boxes saddled on yet with a 4x4 cover and a switch and duplex. Its easy to jump to the conclusion that everything will have a 20A load but the outlets I would ever use to power a real saw pretty much breaker wire to a duplex in its own box and the beauty of piping, screw on another box and add switches.
