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From: reid@Glacier.ARPA
Newsgroups: net.audio
Subject: Re: running speaker wires through walls
Message-ID: <852@Glacier.ARPA>
Date: Wed, 24-Oct-84 23:46:03 EDT
Article-I.D.: Glacier.852
Posted: Wed Oct 24 23:46:03 1984
Date-Received: Sat, 27-Oct-84 03:46:45 EDT
References: <1033@ulysses.UUCP>
Organization: Stanford University
Lines: 52

>    "class 1 wiring, as per local codes" should be used if speaker wires are
> run inside of a wall.  Now, if someone could just tell me what "class 1"
> wiring is....

I think the short answer to your question is that Carver is bragging, very
subtly, about what an enormous monster power amplifier he has built. It's
quite ludicrous to have an audio cable classified Class 1, but in this
circumstance it probably is.

Every wire in a house, even intercoms to the front door, must obey an
electrical code. The National Fire Protection Association (NFPA) publishes a
National Electrical Code (NEC); many localities choose to overrule parts of
it.

"Class 1" wiring is an NFPA category for remote-control, signaling, or
power-limited circuits. They categorize this kind of wiring in Class 1, 2,
or 3 according to the power handled by the wires and the nature of the power
source. Class 1 is for things that border on being dangerous, or whose
failure could have serious side-effects. There are therefore more
restrictions on what you can do with Class-1 wires.  Class 2 is for
low-power low-voltage things like thermostat and intercom wires, and almost
all stereos. Class 3 is for low-power high-voltage things such as
electric-fence conductors that are run indoors.

You can't use Class 2 if the power source driving the circuit is capable of
delivering more than 250 watts or so, and you can't even use Class 1 unless
that circuit is inherently limited to 1000 watts and 30 volts.  Many other
conditions apply. Consult your local library if you care.

Class-1 circuits must be insulated for 600 volts, and must normally use wire
of size 14 or larger. You would probably do this anyhow.  The code
requirements that probably matter to you are that Class 1 circuits are
required to be grounded just like ordinary AC line circuits, and that in
general you are not allowed to pull Class 1 wires in the same conduit, or
run them through the same electrical box, as AC line circuits. You would
probably never even consider running a speaker wire through an AC junction
box, but the code says you are not allowed to. 

There is actually in the NEC a list of particular kinds of wire that are the
only ones permitted for Class-1 wiring. The list is long and tedious. No
electrical inspector would have it memorized; most don't even know it
exists.  The only thing you really need to know about it is that stranded
wire has vastly more stringent limitations than solid wire, and that if you
plan on running stranded wire you should go to your library and get a copy
of the NEC and read what it says about stranded wire and Class 1.  Monster
cable and zip cord do not meet the requirements; hand-made True Litz wire
would also not be permitted. Romex 14+1 will do just fine. My house is
speaker-wired with Romex 10+1.

	Brian Reid
	Stanford
	(currently EE/CS professor; formerly electrician)