I seem to recall that type 7 enclosures are not covered in KS-1, but maybe my remembering is faulty.
eta: I went and looked at the standard. It indicates enclosures suitable for hazardous areas are acceptable.
They don't say one way or the other, the enclosures just have to meet NEMA 250, which includes Type 7, so technically, they COULD be used.
The problem boils down to heat. NEMA KS 1 has a specification for heat rise inside of the enclosure, plus it ALSO has specifications for overload capacity of the switch, switching frequency and an endurance cycle. Those 4 issues combine to make it virtually impassible for a NEMA 7 enclosed switch to pass, or rather, the enclosure size required to pass would make them affordable.
So for an example, a 30A rated switch must be able to handle 150% current, switched 6 times per minute, 8000 times, with the temperature inside of the enclosure not going more than 50C over an ambient of 25C. For a sealed, solid walled exp. proof enclosure, it just can't pass, or if you wanted it to pass, the enclosure would have to be huge.
