Adding Class 2 and Communications Cables to an Existing Power Raceway
A 6,000 ft² warehouse office build-out has a 1 in. EMT raceway running 140 ft from a 120/208 V panel to a new server room. The raceway currently contains three 12 AWG THHN current-carrying conductors for a 20 A dedicated circuit; fill is about 22 percent. The low-voltage contractor wants to add two Cat6A cables for access-control readers and one 18 AWG two-conductor Class 2 cable for a 24 V door-strike power supply through the same raceway because the ceiling is now closed. The Cat6A is CMR, the Class 2 cable is CL3R, and the run passes through a return-air plenum for the last 30 ft. The contractor proposes to pull all three cables together with the existing power conductors and strap them every 10 ft. The electrical inspector has not yet been called.
1. May the Cat6A and Class 2 cables share the EMT with the 20 A circuit as proposed? Explain the separation rules and any exceptions.
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No, not as proposed. Communications cables under Article 800 and Class 2 cables under Article 725 are generally required to be separated from electric light and power conductors. The classic exception is a permanent barrier or other listed separation method; simply pulling all conductors into the same 1 in. EMT with no barrier does not satisfy that. The fact that the power circuit is only 20 A or that the raceway fill is low does not create permission. The contractor must either install a separate raceway for the low-voltage cables, use a listed barrier-type raceway or divider, or find another wiring method permitted by the code and the cable listing. The Class 2 door-strike circuit is still a Class 2 circuit even though 24 V sounds harmless. The inspector will look at the actual raceway and fittings, not just the cable jackets. If the contractor wants to use an exception, the burden is on the contractor to identify and install the specific permitted separation method.
2. What plenum rating is required for the last 30 ft, and what support requirements apply to the cables?
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The last 30 ft is in a return-air plenum, so the cables must be listed for plenum use: CMP for the Cat6A and CL3P for the Class 2 cable. CMR and CL3R are not sufficient in a plenum, even for a short portion of the run. The transition point must be accessible and made with listed fittings or methods; the installer cannot strip back the plenum rating for the last 30 ft. Support is also a code issue: cables must be supported per 300.11 and their listing, typically with listed J-hooks or straps at intervals that do not exceed the cable manufacturer's requirements and do not rely on the ceiling grid or sprinkler pipe. The proposed 10 ft spacing may exceed the listing for Cat6A and is likely to be cited. The contractor should also maintain separation from power conductors and avoid sharp bends that exceed the cable bend radius.
3. The raceway is only 22 percent full. Does that make the proposal acceptable? Explain the fill and derating issues.
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No. Raceway fill is only one requirement; permission to mix power and low-voltage circuits is a separate question. Even if the calculated fill after adding the cables remains below the Chapter 9 limit, the installation still violates the separation rules unless a permitted barrier or separate raceway is used. The contractor should calculate fill using the actual cable dimensions, not just conductor counts, because Cat6A and Class 2 cables have non-round or bundled shapes. If the power conductors remain in the same raceway, ampacity adjustment for current-carrying conductors may also apply, although three 12 AWG conductors alone may not trigger derating. The inspector is likely to reject the job on separation grounds before reaching fill. The correct fix is a separate low-voltage raceway or a listed divider system, with plenum-rated cable in the plenum section and proper support throughout.