Connecting speakers is a favorite topic for debate by audiophiles. Some sing the praises of the sound of special cables, while others claim only the correct gauge is of importance. When it comes to the National Electrical Code, cable for speakers mounted in walls and ceilings must be rated for performance in the event of fire. CL2 and CL3 indicates compliance with Underwriters Laboratory standards, which in turn determines the suitability of each cable for use with the NEC.
CL Cable Designation
Both CL2 and CL3 speaker wire are suitable for in-wall installations. While NEC codes don't specifically refer to home theater use, these do refer to multipurpose wire used for remote-control, signalling and power limited circuits. Underwriters Laboratory testing requires that a cable pass one of two UL tests, selected by the manufacturer, with resultant damage within the limits specified. Each test involves flame testing and evaluation of the damage to the wire that results.
While CL2 and CL3 must pass the same tests for certification, the primary difference between the two cables is in the maximum voltage handling. CL2 cable must accept a maximum voltage of 150 volts, while CL3 handles up to 300 volts. Both are adequate for most speaker installations, and CL3 can be used in place of CL2, though CL2 cannot be used if CL3 is required.
CLP and CLR Designations
Refinements to the CL class of wire, the suffixes P and R are used to denote wire used for particular applications. CLP wire is for use in cable runs through plenum spaces, like the space between the actual and suspended ceiling, where such space has use in the ventilation system, usually as an air return. The insulation of the wire must be such that it does not give off harmful gases when burning, to prevent toxicity in another area served by the same air handler. CLR rating refers to "riser" applications, when cable must go through a floor to another story of a building.
CLX indentifies a wire that is a lower grade. Both CLX2 and CLX3 voltage ratings are available. This designation is largely used to describe cable suitable for residential use with raceways or in non-concealed installations. While voltage handling is sufficient to the task of speaker wiring, the strength and durability of CLX class may require extra care and protection. Cost savings from this grade of wiring should be weighed against the difficulty of repair or replacement.