|Audio Wiring for Speakers
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.
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
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)
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
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.