Plenum-Rated Control Cable Shared With Power in an EMT Sleeve
You are the low-voltage lead on a tenant improvement in Boise. The mechanical contractor asks you to run a 24 VAC control cable from a rooftop VAV controller to a corridor thermostat. The cable is 18 AWG, two-conductor, marked CL2P, and the route is 85 ft through the return-air plenum above the corridor ceiling. At a rated wall, your route joins a 2-inch EMT sleeve that already carries four 120 V branch circuits; the sleeve is 18 in. long. After the sleeve, you plan to bundle your cable with six other Class 2 control cables on J-hooks for the last 30 ft, secured with zip ties every 18 in. The electrical inspector has questioned both the plenum rating and the mixing of cables. The mechanical contractor says the 24 VAC circuit is power-limited, so separation and bundling do not matter. You need to decide what can stay and what must change before inspection.
1. Is the CL2P cable acceptable in the return-air plenum, and what installation limits apply?
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Yes. The P suffix in CL2P identifies a plenum-rated Class 2 cable. In a return-air plenum, 300.22(C) requires wiring methods and cables specifically listed for the environment; exposed Class 2 cable must be plenum rated. CL2P is the correct marking for that location.
That does not make the whole route acceptable. The plenum rating addresses smoke and flame characteristics, not separation from power circuits. The cable must also be installed per its listing, supported and secured so it is not damaged, and kept within the raceway or cable-routing rules that apply to the method used. If any portion of the 85 ft run is fished through a metal raceway, the raceway itself must be suitable for the plenum location. If the cable is exposed on J-hooks, the exposed cable must remain CL2P. A non-plenum CL2 cable cannot be substituted just because the circuit is 24 VAC or power-limited. The inspector's plenum question is answered by the CL2P marking, but the sleeve and bundling questions still need separate correction.
2. Evaluate the 18 in. EMT sleeve shared with the four 120 V branch circuits.
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The shared sleeve is a violation as described. Article 725 separation rules generally prohibit Class 2 circuit conductors from occupying the same raceway, box, or cable-routing assembly with electric light and power conductors unless a listed barrier separates them. An 18 in. EMT sleeve is a raceway, not a de minimis pass-through, and the fact that the control circuit is power-limited does not waive the separation requirement.
The practical fixes are: install a separate sleeve or raceway for the Class 2 cable; remove the 120 V circuits from that sleeve; or use a listed raceway/box assembly with a permanent barrier that maintains separation. Tape, split tubing, or spacing the conductors apart inside the same sleeve is not a barrier. Because the sleeve is only 18 in., a second short sleeve is usually the least invasive correction. Re-inspect the wall penetration after the change: firestopping and the rated-wall assembly must remain intact, and the new sleeve must be installed without damaging the existing branch circuits.
3. Does bundling the seven Class 2 cables require ampacity adjustment, and are the zip ties acceptable?
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For this 24 VAC control circuit, the current is low and the circuit is power-limited, so the usual Chapter 3 conductor-ampacity derating for bundled power conductors is not the primary issue. Bundling still matters under Article 725 because cables that carry power and data or power and control may be subject to bundle ampacity rules, and the cable listing may impose limits. Check the cable manufacturer's instructions and the Class 2/3 cable requirements before assuming the bundle is unrestricted.
The zip ties themselves are acceptable if they are snug but do not crimp, dent, or damage the cable jacket. Support the bundle so the weight is carried by the J-hooks, not by the ties or the terminations. Keep the Class 2 bundle separated from the 120 V circuits; do not use the same J-hook or sleeve as power. The main correction remains separation from power, not the 18 in. tie spacing.