different voltages between switches in same enclosure

[bwieland]

does grouping two switches one at 120v and the other at 277v both have 600v insulation violate 404.8 (b) or any other part of the nec

[don_resqcapt19]

Both systems are grounded systems, so there will be voltage between the two hots. The amount of this voltage will vary based on the phase relationship between the two hots and the amount of phase shift between the two systems. Most combinations will result in a voltage exceeding 300 volts between the two hots.
Don

[harold endean]

Section 404.8 (b) does not allow 2 switches to be side by side and have more than 300 volts between them What you most often see is a 4" square box with a divider in there to isolate the 277 volt switch from the 120 volt switch. Either that or you can just install 2 different boxes with each switch having only their own voltage in each box.