Can low voltage cable share a box, raceway or conduit with high voltage wiring

Updated
Quick answer

Generally no. Class 2 and Class 3 cabling, communications cable and power-limited fire alarm cable must stay out of boxes, raceways and enclosures that hold electric light, power or Class 1 conductors, unless a listed barrier or a permitted exception separates them. The rules are in NEC 725.136 for Class 2 and Class 3 circuits, 800.133 for communications, 760.136 for power-limited fire alarm and 820.133 for coax CATV.

Steps

  1. Identify the circuit class
    Access control, intrusion and most camera power supplies are Class 2 or Class 3. Network, phone and data cable is communications. Fire alarm wiring from a listed panel is usually power-limited fire alarm (PLFA). Coax video is CATV/radio distribution.
  2. Find the governing section
    Class 2 and Class 3 separation is NEC 725.136. Communications is 800.133. PLFA is 760.136. Coax is 820.133. Each covers raceways, cable trays, boxes and enclosures.
  3. Keep separate raceways and boxes
    As the default design. Run low voltage in its own conduit, sleeve or J-hook path and use separate back boxes or a two-gang box with a listed divider.
  4. Use a listed barrier where the code allows a shared enclosure
    Multi-gang boxes and enclosures with a permanent, listed barrier keep the low voltage compartment separate from line voltage terminations.
  5. Respect separation in open runs
    The same sections require spacing between exposed low voltage cable and power conductors unless the power wiring is in a raceway or cable armor, or a fixed nonconductor is in between. Check the spacing value in your adopted edition.
  6. Follow the manufacturer too
    Equipment manuals often add their own rule. DoorKing, for example, tells you to keep entry system wires a minimum of 18 inches from high voltage wires to prevent hum, which is stricter than many code minimums.
  7. Confirm with the AHJ
    Before rough-in on a commercial job, because the adopted NEC edition and local amendments decide which exceptions apply. See also this related page.

Specs & limits

Class 2 and Class 3NEC 725.136
CommunicationsNEC 800.133
Power-limited fire alarmNEC 760.136
Coax CATVNEC 820.133

Common mistakes

  • Pulling a Cat6 through an existing power conduit because there is room. Fill is not the issue; mixing circuit classes is.
  • Landing a relay that switches 120 V in the same compartment as Class 2 wiring with no barrier. Use a separate enclosure or a listed divider.
  • Assuming low voltage means no code applies. Articles 725, 760, 800 and 820 all have installation rules.

Applies to

Also asked as: “can cat6 run with electrical”

Sources

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