From: schmidt@auvax1.adelphi.edu
Newsgroups: rec.audio
Subject: Re: behind the wall speaker wire
Date: 22 Jul 92 05:35:56 GMT
Organization: Adelphi University, Garden City NY

In article <1102@netxcom.netx.com>, pdressne@netxcom.netx.com (Peter Dressner) writes:
> I need to wire for my stereo behind my walls. On some speaker wire,
> there is a warning that it is not suitable for behind the wall
> installation. Why not? What type should I use? The stereo is rated
> at about 40 WPC.
> 
> Thanks in advance.
> 
> Peter

Well, you can't win! I was going to quote you from the National Electric Code,
but after I started this reply, I discovered my copy had disappeared.  I'll
find it for sure two minutes after I post this....  

Most "speaker wire", the clear 18 gauge stuff is actually approved by the UL to
be used as "lamp cord" or such, and is classified as such in the NEC.  I was
going to give you the actual classification code, but without my code book....

The insulation is rated for 300v, but only for use where not subject to
physical damage or "rough usage".  Also #18 wire is only good for about 5 amps,
but is considered "protected" by the 15 or 20 amp fuse or breaker, as long as
the connected load is within its rating (note- the British have a whole
different system, and require fuses in the "plug" to protect the wire from
overload)  These wires are not allowed to be used for "permanent installation"
or to be run through walls, under carpets, through doors, etc, when used as
lamp or extention cords, as they could obviously be very unsafe in case of
overload.  This same wire can be used as "limited power" wiring, such as almost
all speaker wiring, doorbell wiring, etc (class II wiring is under 50 volts,
and with specific current limits.)  When it is used for this application, it
CAN be run whereever you want (except in hazardous or special locations, such
as explosive environments).  The idea is that the power and voltage limitations
are such that you couldn't start a fire, even if you short out the wires or try
to create an arc.  

In the last code revision they put increased flammibility requirements on wire
insulation, not to protect it from starting a fire, but from burning too
vigorously and spreading a fire (possibly from other sources) within a
building.  This is what the CL2, and such is about.  Actually they use
different code letters for each different classifified use for the wire, much
wire now has multiple flammibility ratings.  Once again, if my code book was
here, I'd give you the specifics.  These requirements have little to do with
running the wire through walls, at least in residences, as the same
requirements apply whether the wire is concealed or exposed for class II
wiring.  The only exception is if you run the wire in conduit, then you are
allowed a couple of feet of exposed wire at the ends without the flammibility
rating.  (incidentally, the same requirements apply to telephone wiring, and
that's why much of the new telephone wire looks different than the old stuff, a
lot of the "jk" wire failed the tests.)  

I have never seen the particular warning you mention on a spool of wire, but
I'm willing to bet it was put there to help prevent the Mfr. from loosing a
lawsuit if Mr. do-it-yourself tries wiring his air conditioner with it to the
outlet in the basement by drilling holes in the walls, and later burns down the
house because the 14 amp air conditioner melts the wire, which is, of course
going to melt first in the wall where the building materials keep it from
dissipating heat, and where the fire is going to burn undetected for quite a
while.  

Assuming your stereo is of reasonable size (no 2kw RMS amplifiers!) you can
safely run the zip cord through the wall, under the floor, etc.  I wouldn't
even be too concerned if it isn't fire rated, unless you've got a giant bundle
of it.  The burning carpet, furniture, draperies, etc. in your house are going
to get you long before the little bit of insulation on your speaker wires
does!!  Buy a smoke detector, with working batteries and sleep comfortably.

This flammibility problem is more of a problem in offices, etc where computer
hookups and telephone wiring sometimes begins to cause good size  piles of the
wire.  There was a serious fire in the World Trade Center some years ago spread
through several floors oftelephone wiring closets by burning insulation on
telephone cables, and then there was the the serious fire in the NYC telephone
central office, again fed by burning insulation.  Funny thing is the phone
companies got the Central Offices exempted from these requirements...

You should note that some localities don't use the NEC and may have their own
codes which may be stricter or more lax on this type of wiring.  If you are
really concerned about this, get some fire rated wire.


-- 


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John H. Schmidt, P.E.              |Internet: schmidt@auvax1.adelphi.edu
Technical Director, WBAU           |Phone--Days     (212)456-4218
Adelphi University                 |       Evenings (516)877-6400
Garden City, New York 11530        |Fax-------------(212)456-2424
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