Q. Can I install 120V conductors in the same space with 277V conductors? If the answer is yes, what restrictions apply?

A. Power conductors of AC and DC systems rated 600V or less can occupy the same raceway, cable, or enclosure if all conductors have an insulation voltage rating not less than the maximum circuit voltage [300.3(C)(1)]. Control, signal, and communications wiring must be separated from power and lighting circuits so the higher-voltage conductors do not accidentally energize the control, signal, or communications wiring.

See the following applicable sections of the Code:

  • CATV coaxial cable [820.133(A)]
  • Class 1, Class 2, and Class 3 control circuits [725.48 and 725.136(A)]
  • Communications circuits [800.133(A)(1)(c)]
  • Fire alarm circuits [760.136(A)]
  • Instrumentation tray cable [727.5]
  • Sound circuits [640.9(C)]
Class 1 circuits of Class 2 and Class 3 circuits that have been reclassified as a Class 1 circuit [725.130(A), Ex 2] can be run with associated power conductors [725.48(B)(1)] if all conductors have an insulation voltage rating not less than the maximum circuit voltage [300.3(C)(1)].