Been a while since I was up on NEC code here. When I was...
Class 2 is 50v & 100va and under, no conduit required in most cases. Above that is class 1 and requires "conduit" of some fashion generally.
That said, each cable type / use / location has numerous exceptions. For example, romex in residential. No conduit required where its "protected" in residential. That's typically in walls, attics that are used not for storage, or protected such it cannot be readily damaged by normal use. Protected in the open, typically means the cable is in the middle of whatever wood members your passing through. So a garage without any drywall on the interior, you can use romex as long as its not on the surface of the studs. Still exposed IMO, but meets code. You can run 240v 100A romex without any conduit all day long in this case.
SO cord can be used for 480v 3 phase and many times 100va, in certain use cases and locations. Elevators don't use conduit to make the connections to the passenger car.
Never dealt with solar and far removed from current NEC now, but I would expect there are certain exceptions for solar panels. I know solar has its own sections in the NEC, never paid any attention to them or was required to. For starters, have you seen a panel with an enclosed box for the connection and conduit knockouts? Bit of an issue if NEC requires 100% conduit then. Can't put a splice in conduit under any condition, so what exactly is the market for these connectors if 100% conduit is required then?
It may be that most inspectors are clueless that some of these are being installed in series/parallel strings at fair voltages and currents. They are just generally not aware of whats really going on, make assumptions and pass things especially when its a well known name doing the install. I see a good number of these solar installs and never really paid alot of attention to them. Until now, I would have never expected to see >300v volts @ ~30A on a innocent little connector like this with free air cable. Opening that live is going to be exciting I expect. That stuff just gained a lot more respect/interest next time I'm walking by.
With all the BS OSHA safety crap is around arc flash hazards today, I'm bewildered how a connector like this can be rated for 1KV @ 30A without requiring permanently embossed warnings, high viz colors and LOTO provisions. 1kv AC has an absolute $hitload of safety requirements at any moderate power level. Internally in a building, your going to have to accommodate that with special construction in most cases.