A & E Service Maintenance Co., Inc. Service
Company, Inc.
Electrical Contractors

Audio Wiring for Speakers 6/30/2003
Dear Mike,

All commercial amplifiers have and always had (probably since the 50's) the class of wiring required to be used printed on the back panel. The Class of wiring needed is dictated (currently) per ANSI/UL section 813 testing procedures by the manufacturer and has nothing to do with the NEC nor can it be reliably user discerned from the amplifier wattage, output voltage or impedance.

Forgetting local jurisdictional requirements, the only way then to know what wiring is needed is to read the Class of wiring required from the back panel of the amplifier then look in Art.725 if you don't know what it means.

Sound simple? It should be. But zip cord is the norm and where the wiring is actually inspected, inspectors' just look to see that the insulation complies (IE plenum) and not the Class (IE CL1, CL2, and CL3).

Class 1 wiring for speakers?? It's quite common and this where most of the confusion, problems and frustration lies. Apparently the NEC code panel saw this and felt that clarification of Class 1 audio output wiring was needed because of non-compliance. That is exactly what they did to Article 640.9(C) in the 2002 edition. Now there should be no mistake. If it says, "Class 1 wiring required" on the amplifier, that is how it is to be wired regardless of what output voltage or impedance you use.

The problem is nobody makes a Class 1 approved cable suitable for audio. CL2 and CL3 plenum and non-plenum cables are available off the shelf. If your job requires Class 1 audio wiring your options are pretty much limited to raceway and conduit at the moment. We have even gone so far as to have type TFFN custom twisted (the audio industry likes twisted wiring). We then pull this through conduit to be NEC compliant (Art 725.27).

Also, unlike Class 2 and Class 3, the Class 1 wiring method goes beyond the wire. Class 1 is Class 1, and just like power and light it requires proper connectors, enclosed terminals and splices, etc. Not every manufacturer makes speakers suitable for use with Class 1 wiring and the specs don't say when they do. So, it is up to the installer or specifier to determine what is acceptable.

I would say that the NEC, the electrical industry and the audio industry have some work to do in this area to raise awareness and compliance.

To ease the Class 1 wiring issue, I have proposed an exception to Article 725.27 that would allow the use of a listed type CL3 cable for audio use under some circumstances, when pulled through a raceway or conduit, instead of the individual conductors given in (A) and (B).

Though all commercial amplifiers have the required Class of wiring indicated on the back panel, I have never seen this listed in the specs. You almost have to buy the amplifier first before you can specify the wiring method and speakers. It would also help if manufacturers included an interpretation of the applicable NEC wiring requirements in their installation instructions so that an installer would have less of an excuse to be ignorant.

If you have any thoughts, corrections or criticisms on this I would be happy to hear them. This is a subject that seems to be misunderstood and ignored so anything you can do would help.