CL2 / CL3 In-Wall Wire Rating UL 13 / NEC Article 725 Class 2 and Class 3 Power-Limited Circuit Cable Ratings

What CL2 and CL3 mean

CL2 and CL3 are cable types for power-limited circuits, the low-energy wiring used for speakers, doorbells, thermostats, and security. UL's description of its UL 13 standard says it covers 60 to 250 degrees C power-limited circuit cables used as fixed wiring in buildings, principally for Class 3 and Class 2 circuits as described in Article 725 of the National Electrical Code. The types it names are CL3P and CL2P (plenum), CL3R and CL2R (riser), CL3 and CL2 (general commercial), CL3X and CL2X (limited use), and PLTC.

The two numbers are voltage classes. Windy City Wire describes CL2 as insulated for up to 150 volts and CL3 as rated for circuits carrying up to 300 volts. CL3 therefore tolerates roughly double the voltage, and the substitution rule runs one way: CL3 can replace CL2, but CL2 cannot replace CL3.

How the code ties speaker wire to these ratings

Speaker wire reaches Article 725 indirectly. Blue Jeans Cable explains that audio interconnect cables and speaker wires fall under NEC Article 640, which points to Article 725. In Blue Jeans' reading of the code, the in-wall rule is that CL2 and CL3 are always permitted, CL2X or CL3X may be used in a raceway (or without one, if under 1/4 inch in diameter, in a one- or two-family home), and higher-rated substitutes such as CM, CMP, CMR, CMG, CL2R, CL3R, CL2P, CL3P, and PLTC are also accepted. Blue Jeans adds that CL3 is often the marking printed on in-wall speaker wire spools.

A model-code summary of the International Residential Code reaches the same place: cable installed inside wall cavities must carry a CL2 or CL3 listing, and unlisted speaker wire in a wall cavity is a code violation that must be corrected before the wall is closed. Article numbers shift between code editions and local authorities adopt different editions, so confirm the current text with your inspector before pulling wire.

CL2 vs CL3: the voltage math

Speaker circuits sit far below either limit. The RMS voltage across a load is the square root of power times resistance. A 100 W amplifier into 8 ohms puts out about 28 V RMS, or 40 V peak. A 500 W amplifier into 8 ohms reaches about 63 V RMS and 89 V peak (arithmetic from V = sqrt(P x R)). Even that extreme case is under CL2's 150 V insulation rating, so the voltage class does not decide which cable a speaker run needs. The IRC summary says residential speaker systems generally fall in Class 2 when fed from a listed amplifier with internal overcurrent protection. That leaves the choice to price and availability, and CL3 is the safe default because it can be used anywhere CL2 can.

Which letter suffix where

The suffix matters more than the number. Blue Jeans lists plenum spaces as requiring CL2P or CL3P, with CMP as a permitted substitute, and the IRC summary says the same for air-handling plenum runs. Riser runs through floors in one- and two-family homes can use plain CL2, CL3, CL2X, or CL3X. In commercial or multifamily buildings, where cable penetrates more than one floor without a raceway or shaft, CL2R or CL3R must be used. A spool of CL3 wire is fine inside a stud bay in a house, and it is not acceptable in a plenum ceiling.

Buy the P version only where the code requires it. For a typical basement or bedroom run through studs, plain CL2 or CL3 is the correct and cheaper choice. For a run that crosses a return-air plenum or a drop ceiling serving as one, buy the P version.

Where this matters in a home theater

The use case is a surround or Atmos height speaker fed through a wall or ceiling, usually 14 to 16 AWG. The IRC summary says conductor size is not regulated by the residential code, with 16 AWG suiting most runs and longer runs calling for heavier gauge, so the CL marking and the gauge are two separate decisions (see speaker wire gauge and the speaker wire tool). The same summary says low-voltage cable cannot share a raceway or enclosure with 120 or 240 V conductors without a listed barrier, which is why speaker runs and AC feeds go in separate stud bays or sleeves.

The listing question applies to products as well. Blue Jeans notes that some of the cable it sells, including all Canare cables, is not NEC-rated and may not satisfy a strict inspector. A cable that works electrically is not the same as one that is approved for the inside of a wall.

Common confusions

"In-wall rated" is not a thicker or better-sounding wire. The rating describes the insulation voltage class and the listing, not conductor size or sound quality, and a CL3 16 AWG pair carries the same signal as an unrated 16 AWG pair. Another confusion is the plenum suffix: P means plenum, R means riser, and X means limited use, so a CL3P cable can substitute downward but a CL3 cable cannot go in a plenum. Finally, line-level interconnects and HDMI follow different families (Blue Jeans cites CATV types under Article 820 for in-wall video), so check the right marking for each cable you pull. Wiring layout is covered in the home theater wiring guide.