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In several of the rooms of the house I moved into last year (built 1973, USA), there are blank wall plates. I've removed a few to investigate and found somehting similar to the below pictures each time: a loop of what appears to be thick brown electrical cable, accompanied by a foot or so of thin 2-conductor black cable that is either insulated with rubber or a very flexible plastic, and covered in orange muck.

I've given the large loop a god tug and it doesn't appear to be an off-cut tucked back up into the wall. If it is, it's jammed in there pretty good.

Neither appears to carry any voltage according to a NCV tester, and it doesn't resemble the mains wiring in any of the live outlets or switches (which is all white plastic NMC and generally a bit thinner than the thick brown wire here).

I'm not intending to do anything with it at this point, just curious as to what it is/was.

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    Looks like lamp cord. Not appropriate for boxes carrying line voltage, but it may have been intended for speaker wiring. Also, if the other cable is line voltage, you are not supposed to house it in the same undivided box as low voltage wiring. However, the other cable might also be some type of media carrier. – bib Oct 7 '17 at 18:55
  • The fact it seems to have been housed with very different (possibly high voltage) wiring was what made it so confusing to me too. I routinely install Cat6 as part of my job so I know about not mixing low voltage with line voltage. As I said, neither appears to be carrying any voltage at present in any of the locations I've opened up, so I'm confident that whatever it was, it's not a hazard now. Speaker wiring is a possibility. – Trelfar Oct 13 '17 at 1:57
  • The smaller cord looks like speaker wiring. Perhaps you should take off all the blank covers and see if there is one where there are multiple cords. That would suggest that was the one the stereo receiver could connect to and the others are for speakers. – Jon Nov 16 '17 at 17:49
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Partial answer: the larger cable is Belden 8290 shielded twin lead TV antenna cable, which was introduced the 1960s and so is probably original to the house.

It's been literally years since I posted this question so in all likelihood nobody will happen upon this, but while working in my attic today I uncovered an old UHF/VHF antenna that was laying on the rafters and buried by the blown cellulose insulation. After digging it out a bit I immediately recognized the wire it was connected to as my mystery large wire and could finally get a good look at it.

There was no sign of the smaller wire in the attic so what that was used for remains anybody's guess.

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    Thanks for coming back; if this is the best answer, feel free to accept it. – Daniel Griscom Nov 26 '20 at 23:22
  • Since the new answer bumps the question to the top of the pile, it most certainly will be found! (As you may have noticed.) Thank you, indeed, for coming back to answer your own question, and please do click the check-mark next to it so others know it's been answered. – FreeMan Nov 27 '20 at 16:02
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Given that the large loop (that will be a multi-conductor cable - if you could see more of the writing on the jacket you could tell exactly what sort of multiconductor cable without cutting it open - It's Belden, based on "BELD" visible) is uncut, I'd guess whatever this was planned for was never actually installed. The "Zip-cord-like wire" also resembles certain types of telephone two-wire service cord and in any case was probably intended for something low-voltage or it would not have passed inspection even in 1970.

But the fact that the large cable loop is uncut leads me to think that this was planned for, and then never completed.

You could look around in the basement or where the telephone service comes into the building for wire ends that look like these.

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  • I would agree on high end spec homes we used to pre wire both phone and intercom circuits in most rooms but usually only terminated 1 phone location unless the home was purchased prior to finishing. The zip or 2 wire could have been for a audio feed, if a intercom most of the intercoms back then had 1 wire for each location with a common on the nicer units so you could call a specific location (if there were 6 locations a total of 7 wires went to each so only that only 2 zones could be active or all of trying to find someone) back then there was a listed 14 fine strand speaker wire. – Ed Beal Dec 24 '17 at 22:42
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I believe you are showing regular zip cord.

What is zip cord? (Wikipedia)

Excerpt:

Zip-cord is a type of electrical cable with two or more conductors held together by an insulating jacket that can be easily separated simply by pulling apart.

Typical uses include lamp cord and speaker wire.

Conductors may be identified by a color tracer on the insulation, or by a ridge molded into the insulation of one wire, or by a colored tracer thread inside the insulation.

Zip cords are intended for use on portable equipment, and the US and Canadian electrical codes do not permit their use for permanently installed wiring of line-voltage circuits.

enter image description here

Certainly no licensed electrician would have installed such wiring.

One of the biggest concerns is that if it is pulled it might chafe off some of the insulation (perhaps at bends in a conduit), and then you could end up with a hot conduit. Either that or a breaker that appears to blow for no apparent reason.

In any case, this is not a good thing to find in your wall.

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    Right now I'm viewing it as a mystery rather than a concern. If either set of wiring was energized the NCV would have picked that up, so I'm pretty sure this wiring is no longer live. I won't be pulling on it any more though, just in case - at least until I can figure out where it goes. The attic immediately above the room where this photo was taken is accessible but is filled with blown cellulose insulation, which doesn't make it easy to locate wiring. – Trelfar Oct 13 '17 at 2:04
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Likely an old intercom system. These used to be quite popular in the 60s and 70s, but are often removed or inactivated, leaving behind mystery wires in the walls.

enter image description here

The smaller wires are speaker/signal wires for the units and the larger wires to power the systems. The signal wires wouldn't carry any voltage without units installed and the power wires were likely disconnected at the breaker when the units were removed, hence no voltage on any of the wires now.

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