Applications: Sound/Audio, Indoor Applications, Intercom Systems
Rating: CM and CL3 (Ok for CL2 uses as CL3 is a stricter code common in commercial applications)
NEC Article 640: Audio Interconnects and Speaker Wires
Audio interconnect cables and speaker wires fall under Article 640, and so whether they can be installed in-wall or in other specific settings will depend on that article. Under NEC 640.21(C), these are in turn governed by Article 725, "Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits."
General installation of wiring, including installation inside of walls, is governed by 725.61(E), the principal features of which, for our purposes, are:
- (1) CL2 and CL3 are always permitted;
- (2) CL2X ("X" is a residential suffix, signifying a lower grade than plain CL2) or CL3X may be installed in raceways;
- (3) CL2X or CL3X, if under 1/4 inch in diameter, may be installed in a 1 or 2 family residential dwelling without a raceway; if nonconcealed, it may also be installed in multifamily dwellings.
So, if a cable isn't marked CL2 or CL3, is it suitable for in-wall installation? It may be. The NEC allows cable of a higher rating to be substituted for a lower rating, and therefore, any of the following may be used: CM, CMP, CMR, CMG, CL2R, CL3R, CL2P, CL3P, PLTC. CMX also may be used where CL2X or CL3X is required.
In a plenum, 725.61(A) governs; CL2P or CL3P are required, and CMP is a permitted substitution.
A riser presents a bit different situation, governed by 725.61(B). If you're in a single or two-family dwelling, CL2, CL3, CL2X and CL3X may be used (and, of course, any of the substitutions listed above). In a commercial building or multifamily dwelling, any of those cables are permitted if they are installed in metal raceways or located in a fireproof shaft having firestops at each floor. In a commercial or multifamily building, without a raceway or shaft, if the vertical run of the cable penetrates more than one floor, CL2R or CL3R must be used (or any of these substitutes: CMR, CMP, CL2P, or CL3P).