Class 2 Access-Control Run Through a Packed Wall Cavity
A low-voltage crew is retrofitting access control in a nine-story Atlanta office building. On each floor, the electrician has drilled 1-1/8 in. holes through 2x4 studs at mid-height and pulled two 12/2 NM cables and one 14/3 NM cable through the same holes. The low-voltage plan calls for five Cat6 cables and two 18/2 cables for door-position and request-to-exit devices to share those holes for a 22 ft run; the cables are supported on J-hooks elsewhere. Above the ceiling, the Cat6 enters a 4 in. square junction box that contains a 120 V splice for the corridor lighting, and the box has no barrier. The ceiling cavity is used as a return-air plenum. The lead installer says Class 2 cable is exempt and proposes to fire-caulk the penetrations and move on. The AHJ enforces the currently adopted NEC, and the project has a fire alarm and access-control inspection in five days.
1. Identify the separation and plenum violations in this installation. Explain why the installer's claim that Class 2 cable is exempt is wrong.
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The access-control and door-position cables are Class 2 circuits if they are supplied by a listed power-limited source. Class 2/3 conductors are not exempt from separation rules. Under Article 725, they must generally be separated from electric light and power conductors by at least 2 in., or by a permanent barrier, unless a specific exception applies. Sharing the same drilled stud holes with two 12/2 NM and one 14/3 NM cables does not provide that separation. The junction box is also a problem: Class 2 conductors entering an enclosure with 120 V splices need a barrier or a separate box.
The ceiling is a return-air plenum, so Article 300.22(C) applies. Cables in that space must be listed for the plenum, or be installed in a raceway or other permitted method. Fire-caulking the penetrations does not make nonplenum cable acceptable and does not cure the separation violation. The installer is confusing firestopping with electrical separation and plenum listing. The fix must address both the shared holes and the environmental air space.
2. Describe the least disruptive compliant remediation and the inspection sequence you would use before the five-day deadline.
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Pull the Class 2 cables out of the shared stud holes. Drill separate holes for the low-voltage cables, or sleeve them in a listed raceway that maintains the required separation from the NM cables. Keep the low-voltage bundle on its own J-hooks and do not strap it to the NM cables. At the ceiling box, either replace it with a box that has a listed integral barrier or install a separate box for the Class 2 cables. In the return-air plenum, use plenum-rated cable or a permitted raceway; do not rely on fire caulk for either separation or plenum compliance.
Sequence the work so the rough-in is corrected first, then firestop only the penetrations that actually require it. Photograph the separated holes, barrier, cable markings, and J-hook spacing. Megger or certify the Cat6 runs after the rework, then request the access-control inspection separately from the fire alarm inspection if the AHJ allows. Give the AHJ a marked-up sketch showing the old and new routes. The goal is to show a complete correction, not a cosmetic patch that leaves the same violation behind the drywall.
3. The door-strike power supply is listed Class 2, but the strike circuit is planned to run 40 ft in the same EMT as a 120 V corridor circuit. What must change, and what else should you verify?
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The strike circuit cannot share that EMT with the 120 V circuit unless the raceway has a listed permanent barrier that separates the compartments. A listed Class 2 power supply does not waive Article 725 separation. Use a separate raceway, a listed divider, or a different wiring method. If the circuit is reclassified as Class 1, different rules apply, but the installer cannot simply call it Class 2 and ignore the power conductor.
Also verify the power supply listing and output rating against the strike inrush current, the conductor size for voltage drop, and the door hardware fail-safe/fail-secure requirements. Confirm that the strike circuit is not run in the plenum without the correct cable or raceway. Check that the access-control enclosure is listed for the environment and that the strike wiring is not inadvertently connected to the 120 V circuit through a shared neutral or a miswired relay. Finally, get the AHJ's interpretation in writing before the inspection, because the raceway separation issue is visible and will likely be cited.