ECN Forum Forums General Topics of the Trade General Discussion Area 120v and 277v in the same box?

While it may not be a great idea, as it tends to confuse the next guy, there is nothing in the code that prohibits this, in general. Following the high voltage/low voltage color code is helpful and so is careful labeling, but as long as the insulation of all wires is at least 300 volts,(THHN is 600 volt) its OK.