I was recently at a residence where they had two separate and distinct switch boxes stacked on top of each other. The upper switch box was recently put in by another electrician and the lower switch box has been in use for a few years. Does this stacking of switches (One on top of the other spaced by approximately 1.5 inches) violate the NEC? If so, where in the code? I have read over Article 404 Switches and did not find any helpful information.