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I recently moved into a new house and there are cat5e sockets in each room which go through the ceiling into a media room. In some places in the rooms there are cat5e cables which do not have a connector. There are also cables with no connector in the media room, which lead into the ceiling. I suppose these are ends of connected cables. I'm very interested in connecting one of these unterminated cables in the rooms to the media room. Is there an easy way to check which of the ends in the media room is connected to the end in the place I'm interested in? Unfortunately there are dozens of these cables in the media room, so I really don't want to add a connector to all of them just to test this. Especially since I have never added a connector to a cat5e cable, so I probably will be super slow... unfortunately there are no labels whatsoever on the cables.

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    You might not get that lucky, but have a look for sharpie markings on the cable jackets, as opposed to proper labels which you looked for already and did not find.
    – Ecnerwal
    Commented Feb 16, 2022 at 1:03
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    Put ends on them. It's a good skill to have. Then use a tester.
    – gnicko
    Commented Feb 16, 2022 at 1:25
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    Keep in mind that people can use cables for unexpected and sometimes inappropriate applications . I was surprised to see a bunch of CAT6 in the crawlspace with no sockets in the house - turns out someone ganged 2 pairs into one conductor and used CAT6 for low volt DC lighting. Now thats on the TODO list to rewire....
    – crasic
    Commented Feb 16, 2022 at 13:49
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    @J... So it was YOU :) :). One of the benefits, I find, of application appropriate parts is that if you follow directions, you get a compliant system. Terminating 8wires to 2 wires can be done in many different ways, most of them are not appropriate, some of them may be nominally OK. Using PoE would be the commercial solution , but even then it is rated to only 60W on 4 pairs.
    – crasic
    Commented Feb 16, 2022 at 15:01
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    @J... Heh...yeah but those are just expensive testers
    – gnicko
    Commented Feb 17, 2022 at 0:22

4 Answers 4

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Yes there are specialized tools for that. Search for "tone generator and probe" or "wire tracer" or similar phrases. (image credit: grainger.com, fiberoptics4sale.com)

Fluke Pro 3000

Tempo 701K

However, you can almost as easily use less-specialized tools such as an ohmmeter or volt meter. You might make yourself an adapter consisting of a wall jack with pigtail wires hanging off it, or a cut-off patch cable and a coupler, so that you can easily and non-destructively convert an already-terminated end into bare wire ends.

At the far end of the cable pick a pair of wires, for example the brown and white/brown, and short them together. Then go to the media room where all the cable ends are found. Open up each cable, strip the ends of the chosen pair of wires, and measure resistance between the two. Most likely the resistance will be infinite, meaning the cable you're testing is not the one you're hunting for, or else the resistance will be low (say under 50 ohms) indicating that you've probably found the cable you were hunting for. When you find a candidate, un-short the far end and confirm the resistance goes infinite to be sure.

A similar process could be employed with a volt meter and a battery if an ohmmeter were unavailable.

Terminating all those cables really might not be such a bad idea. Consider the time it'll take to do all that opening of cables and stripping of ends. Now consider if that time were instead invested to put on the 8P8C/RJ45 connector on each of those cables, or to punch the cables down onto a patch panel. The first few will be slow but you'll gain confidence and speed quickly. With terminations on the cables the process of testing which one is which becomes a quick plug-and-check operation. That could still be done with a meter, but with terminations on the cables you also open up the possibility of using a cable tester to simultaneously identify which is which and also confirm it is wired properly and ready to use. Simple cable testers like the one pictured below may only check that the conductors are in the correct sequence; more expensive models can test the electrical quality of a cable. (image: mscdirect.com)

Jonard MCT-468

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  • The battery method has the advantage that it will not falsely identify damaged cables. The ohm meter method has the advantage that you can wire different patterns on the end of each cable and then make all the measurements.
    – Jasen
    Commented Feb 16, 2022 at 3:54
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    To avoid falsely identifying damaged cables, I connect a 1k resistor using a terminal block. A multimeter readily distinguishes this from other possible conditions.
    – grahamj42
    Commented Feb 16, 2022 at 8:50
  • With a decent multimeter, you can connect different resistors such as 1K2, 1K5, 1K8, 2K2 across different pairs of wires (not wires in the same twisted pair) and thereby diagnose mis-terminated cables including reversed pairs from the other end, by seeing what is connected to what with what resistance. But the simple cable tester is quite cheap and a lot easier to use.
    – nigel222
    Commented Feb 16, 2022 at 11:52
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    I agree with the final point - go ahead and put ends on all the cables. At some point you, or the next owner, or one of your (future?) kids, will want to use another one of those cables. May as well be ready now. Saves having to drag out all the tools again in the future and relearn how to do it.
    – FreeMan
    Commented Feb 16, 2022 at 12:28
  • The other advantage of a tone source over other methods, is that you can wave the receiver at a mid-point on the cable and hear the warbling tone. You can identify a cable from within a bundle, without access to the end.
    – Criggie
    Commented Feb 18, 2022 at 2:22
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There's a good answer already for use of technology, both low and high.

If there's enough cable to see what directions the foot markings are going, and they only used one box of cable, you can also deduce likely cables to check by what their foot markings are. i.e. if your desired cable has 602 ft marked near the end, and you find 600 ft marked 2 feet closer to the ceiling entry, your media room cable is going to be 500-something ft, and you might even be able to guess at the something by how far it is from the room you want. In any case, it will be the one closest to 600 of what you find there (so if you find 580 and 560, 580 is the one to check first.)

This can be harder if they used more than one box of cable, but that's rare for home jobs with the cables not labeled. Pros bring multiple boxes, but pros also label cables, almost universally. Homeowners tend to get one box and are more likely to feel sure they will remember which one is which.

Network cable in the US comes 1000ft per box and is foot labeled every two feet from 1000 to 0 (probably marked in meters every meter if not in the US.) There's a whole bunch of info that's the same every 2 feet, and the number of feet left in the box, which changes.

Again, people do the darnedest things, but in general I'd expect the numbers to go down towards the media room, as in my example, as it makes the most sense to leave the box of cable in the room where all the cables go, and pull out of it to each room, rather than move the box around to each room and pull back towards the media room.

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    I can confirm that at-least some pull boxes are marked in meters outside of USA, the ones i've looked closely at had some large offset ( eg I just saw "048591m") so boxes from the same pallet will probably have non-overlapping ranges. it still comes in a 1000 foot box but we call it 305m (well there maybe 8 inches extra, I have not checked)
    – Jasen
    Commented Feb 16, 2022 at 3:45
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    Meters/feet can count up or down when pulled from the box. I have seen both.
    – fraxinus
    Commented Feb 16, 2022 at 20:37
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You could stick a patch panel in the media room to make a tidy job of it.

Then get a toner (even a cheapo one from eBay) you can then connect it to the panel and tone the other ends to identify them.

Then label them up and fit keystones to them ones you want to use. Way less faff than crimping rj45's on.

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    Cindy? Who is that? Commented Feb 16, 2022 at 22:05
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    Punching down to a block is so much easier than putting ends on. If I don't have one, I'll punch down into a jack and use a patch cable.
    – Mazura
    Commented Feb 17, 2022 at 1:44
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    There are a large number of heffalump traps you can fall into if you choose to put plugs on the ends of solid-core cable, starting with buying the wrong plugs or being sold the wrong plugs by a vendor who doesn't appreciate that not all plugs are equal. Use punch-down, seconded.
    – nigel222
    Commented Feb 17, 2022 at 10:05
  • Solid core fails quickly when flexed - which is why we have stranded core flyleads and patch leads. In-wall cabling can be sold core, but your exposed wiring should be stranded.
    – Criggie
    Commented Feb 18, 2022 at 2:21
  • @RibaldEddie my phone keyboard hates me Corrected now
    – GrantH
    Commented Feb 18, 2022 at 8:53
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If you apply a low ac voltage to one of the cables, you could probably pinpoint it using a cheap and simple wire tester that relies on magnetic fields (the pens that light up when in proximity to a live wire). Required voltage to give a reading you probably need to test, but I'm assuming it would give a reading at 24v already. Needs to be ac though, I think.

Another option would be to use re-usable connectors. Some keystone are reusable, so one connector on the cable you want to find, then move around the reusable one in the media room and either use an rj45 cable tester or you can plug devices into each end.

If you are fine with cutting and peeling two wires in the cable, a simple volt meter and a battery, then a multimeter/voltmeter is all you need as well.

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    All of these have been covered in other answers.
    – FreeMan
    Commented Feb 21, 2022 at 12:25

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