What requirement not to mix voltages? You are always permitted to mix power circuits as long as all conductors are rated for the maximum voltage in the raceway and the maximum voltage is 600 volts or less. It is not a code violation to have 120/240 circuits, 120/208 circuits and 480/277 circuits in the same raceway with each other. When you have control or signaling circuits, you can't, in general, mix them with power circuits. You need to apply Article 725 for those circuits.
Don
