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Discussion Starter · #1 ·
There are scads of wires at Home Depot. Do I want solid or stranded? Two individual wires, or a one where they share the same insulation (like lamp cord). I hear people talking about lamp cord, and architectural wire, and CL2 and CL3, plenum, etc. Someone even said somthing about using extension cord!


I assume I want 12GA, unshielded, stranded stuff that looks like cheapo speaker wire from Radio Shack, but I haven't seen that written anywhere. I'm going to be doing an in-wall installation, so I don't want to find out later that I bought the wrong stuff.


Can anyone explain which spool at Home Depot I should be looking for?


(oh, and they're 100W 8ohm speakers and ~25-30' runs for the rears)
 

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You would want stranded wire, preferably each conduit in its own jacket, then inside a third jacket that encompasses the first two. The clear jacket stuff is known to turn the copper green through oxidation.


I don't know if you are set on Home Depot or not, but this generic speaker wire from Parts Express is hard to beat. With the 4 conduit type, you can twist two pair together on each end to give you an 11 GA cable.

http://www.partsexpress.com/webpage....er=0&sm=1&so=2
 

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If the speaker cable is going int the wall, in all likelihood your local electrical code requires that it have a UL CL2 or CL3 rating. There is another recent post of mine floating around one of the forums here on the subject. To make it short, you want 12 ga. twisted pair architectural cable with a CL3 rating. This is what I have in my walls:

http://www.partsexpress.com/pe/showd...number=100-740


Less than $.20/ft. Monster at more than $1/ft. is no better. Don't know if your HomeDepot has similar. What is stocked varies from store to store. I got mine from PartsExpress.
 

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Discussion Starter · #6 ·
Thank you for the advice about CL3 and PartsExpress cable. Unfortunately, I want to pull the cable tomorrow, and I'd be pretty sore if I drove to Ohio and back between now and then.


I'll look for the jacketed UTP 12GA in CL3. If I have to rip it all out in ten years due to oxidation, so be it. I'll still come out ahead compared to buying fancy stuff.


One question I have about this business of clear cable turning green inside after a while. Are we 100% sure that's not also happening invisibly inside opaque insulation cable too?
 

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UTP is untwisted pair. You want twisted pair if you can get it. If you cannot, do not sweat it. The problem with copper wire turning green is occurs with some cheap clear vinyl speaker cables. Better clear vinyl speaker cables don't have this problem. Neither do other kinds of insulation. You should not have to replace your speaker cables after 10 years. Would you plan on replacing your electrical wiring after 10 years?
 

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Oxidation (up to a point) doesn't affect the electrical characteristics of the wire. And in-wall you won't see it anyway.


(And it's not oxidation; the copper is reacting with the chlorine (?) outgassing from the jacket.)


Also look at the underground cable in the outdoor LV lighting area. The 12 AWG black cable is cheaper and tougher than the "speaker wire" they sell.
 

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Never head of a corrosion problem with Carol or any other in-wall cable. Perhaps some of the clear stuff sold under the Carol brand has this problem?


I don't think most underground low voltage cable has the appropriate UL rating for in-wall use for an installation covered by any flavor of the NEC.
 

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Quote:
Originally Posted by DMF
(And it's not oxidation; the copper is reacting with the chlorine (?) outgassing from the jacket.)
Yep, copper oxide (cuprous oxide, Cu2O) is red to deep red or even black. This would form naturally. If it's green, it's not a copper oxide.


Cupric oxide (CuO) is black and formed under specific conditions.


Cuprous chloride (CuCl) could be what you're seeing, but it's usually greyish/whitish. However PVC, especially cheap stuff, does offgas considerably. I'm not sure if it's chlorine coming off or one of the plasticizers.


The bluish/greenish stuff is copper acetate, Cu(CH3COO)2·H2O and could be formed if PVA (polyvinyl acetate) was used as a plasticizer.


As DMF pointed out, this is all cosmetic. The thickness of these formations does not significantly affect the gauge of the wire.

Quote:
Also look at the underground cable in the outdoor LV lighting area. The 12 AWG black cable is cheaper and tougher than the "speaker wire" they sell.
This stuff is quite good - I used a few hundred feet to wire a model railroad. However it's not very flexible, hard to strip due to the insulation's extreme thickness, and would be very difficult to insert into binding posts or banana clips.


But it's very, very tough. The jacket is even UV-resistant for outdoor use.
 

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I understand the concept behind UTP and I also understand that shielding is better. Of course this will not always matter. However I do plan on running it through the walls and most like near or even across other cables (God I hate the construction in Texas). However I am having a really hard to finding a decent gauge shielded cable, foil, braided something. Can anybody out there help?
 

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A sheild will hve no effect on a speaker cable.

A speaker is a low impedance load, it's extremely difficult to induce enough current into this circuit to cause any deflection of the speaker cone. In other words, speaker cable isn't sheilded, because it doesn't need to be.
 

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Thanks for the quick reply.


However I can't see how this can possibly be true. If it were then there would be no sense in using twisted pair either. However we see that all over the place. Additionally I have seen many times where a speaker wire or audio cable (I suppose this could be different) was laid across a power cable. This produced an irritating hum from the speaker. Heck my kids just did this the other day.


Although you explanation may make a good argument for why only TP is necessary.
 

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Quote:
This produced an irritating hum from the speaker. Heck my kids just did this the other day.
try it for yourself. Lay a speaker cable, connectoe to a speaker and an amp across a power cord...what do you hear?


Quote:
However I can't see how this can possibly be true.If it were then there would be no sense in using twisted pair either.
Look up impedance, when you understand that, you'll understand why twisted pairs or coax is used. It should help to understand the effects of the sheild as well.


Speaker circuits are low impedance and have no gain.

Quote:
Although you explanation may make a good argument for why only TP is necessary.
Twisted pair isn't necessary for speaker circuits either.
 

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Quote:
Originally Posted by TonyBDA
try it for yourself. Lay a speaker cable, connectoe to a speaker and an amp across a power cord...what do you hear?
Just to be clear I have already dealt with this on many occasions throughout my life. And I was citing one of those times from just a couple of days ago. My kids created a problem by moving a cable and I fix it by moving it back. By moving it off the power cord. BAM!!! instant fix, yes that was the issue. Great place to start looking, easy to check and has been the fix on many occasions in the past. Maybe I don't fully understand impedance, but know what works. :cool:
 

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Tony gave you the correct electrical explanation of why a power cord shouldn't produce the hum in speaker wire. If you laid that power cord over the speaker wire near the amp input and your input connectors were not tight or faulty you might get the hum in your speakers, and if you move it further away from the amp input connectors the hum indeed may abate. But this is still consistent with Tony's explanation. Although the speaker is a low impedance load with no gain, and therefore has good immunity to interference, the amp input has much higher impedance and lots of gain. So if that objectionable power cord were near an amp input with loose or faulty connections then you could get the hum effect described.


Back to the original question, regular old stranded copper 12ga wire should work fine. Twisted pair is OK but not necessary, and if your running the wire in the wall get plenum certified cable so you don't get caught in an insurance problem.


MT
 

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Quote:
Originally Posted by MikeTz
Back to the original question, regular old stranded copper 12ga wire should work fine. Twisted pair is OK but not necessary, and if your running the wire in the wall get plenum certified cable so you don't get caught in an insurance problem.


MT
Plenum cable is not necessary in typical home wiring. Plenum cable is used mostly in commercial construction where the cabling is run in the spaces above the ceilings that are also used as a return air space for the HVAC equipment. Thus the term "Plenum".


These spaces typically don't exsist in a home, with the exception of some areas between studs that are used for return air to the HVAC equipment. These spaces won't typically be used for speaker wiring since there is usually a sheet metal return duct attached to the top/bottom (depending if the ductwork is above, or below the room) of the wall. If you use this space for wiring, you usually have to deal with fire blocking, and it makes the installation difficult. If you do use these spaces, then plenum wire is the code.


NEC does require the use of CL2 or CL3 for concealed low voltage wiring in a home, and basically because of the jacketing. to paraphrase, the NEC requires that concealed wiring shall not contribute to a fire, in the unfortunate event of one.
 
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