How come?
"Voltage Between Adjacent Devices
A snap switch shall not be grouped or ganged in enclosures with other snap switches, receptacles, or similar devices, unless they are arranged so that the voltage between adjacent devices does not exceed 300 volts, or unless they are install in enclosures equipped with permanently installed barriers between adjacent devices."

Fine, but it's OK to install a single switch (Leviton makes them with ratings of up to 40A, 3 pole/20HP 600V) or a 480V recp in the box.
I Don't Get It [Linked Image]