Mystery cables

[Bert Coules]

A few years ago I had some fairly extensive wiring work done on my bungalow which included the installation of an ethernet network with wall sockets throughout. The cables were all routed into a small spare room, labelled, and terminated with RJ45 plugs to await my chance to arrange a proper equipment hub area.

Today, in the section of the loft immediately behind the future hub I found two trailing data cables, with plugs but unlabelled.

The thing is, I have no idea where they come from. All the wall sockets are accounted for and twinned to known cables in the room. And short of ripping up floors and gouging out walls I can't see any practical way to trace their route.

It's a mystery and is probably going to remain one.

[Andy Burns]

You could buy a cheapish cable tracer?

[Bert Coules]

One of those tone-generating probe devices you mean? Do they work for well-buried cables? I suppose I'd have to sweep every part of every wall until I found a signal: a long job (unless luck kicked in early) but ultimately worth it if it gave me answers.

[Chris Green]

If you really want to find out get a cheap cable tracer, the sort that squirts an audio signal down the wire and has a detector that you wave around to trace the route. I have one and it's invaluable for working out where mystery wires go.

[Fredxx]

+1

Even a cheap Chinese ones seem to work well.

[ARW]

Mine will find a cable behind plasterboard. But I knew roughly where I was supposed to be looking.

[Harry Bloomfield, Esq.]

It happens that Bert Coules formulated :

Yes!

Better than digging them out of the walls along their entire length.

[Robin]

Could be cables the installers ran somewhere by mistake after misreading spec.

Leaves me wondering though. You have N sockets and N cables terminated with labelled plugs. But do you have evidence (other than the installer's word/invoice) that all the plugs are connected to the relevant sockets?

[newshound]

They must end somewhere. If you can't find the other end they will never be any use to you. If you find another end then a cheap cable tester (volts at one end, lights at the other) is the easiest way to confirm you have found them, also which is which, also whether they still work.

Or they might be ones that were found to be dead after installation, and just left with only one end accessible.

[items4sale]

Perhaps they run back to phone sockets to support ADSL or to support FTTP/FTTC/FFTH or for a cable modem?

[Bob Eager]

First check that they are not connected to each other.

[Chris Green]

Since you already know where one end of the cable is you simply follow it from there with the tracer.

[Bert Coules]

Many thanks for all the replies.

I hadn't thought to see if the two cables were connected to each other - which I suppose would mean that they were probably two ends of the same cable - but I've now checked and they're not.

Assuming that they must go *somewhere* the logical conclusion is that there are two wall sockets that aren't immediately apparent, presumably because they're behind bookcases or filled shelves (of which there are a large number). Since the furniture went in after the wiring was completed, I imagine I must have decided at the time that access to those particular sockets could happily be sacrificed in the name of storage and then I went on to forget about them. But why the trailing ends in the loft aren't labelled I've no idea.

So - a lot of shifting or a cheap cable tracer. I'm grateful for the information about the latter.

[Bert Coules]

That will be simple enough until they vanish under the flooring in the loft and head off to who knows where.

[Bert Coules]

Many thanks for all the replies.

I hadn't thought to see if the two cables were connected to each other - which I suppose would mean that they were probably two ends of the same cable - but I've now checked and they're not.

Assuming that they must go *somewhere* the logical conclusion is that there are two wall sockets that aren't immediately apparent, presumably because they're behind bookcases or filled shelves (of which there are a large number). Since the furniture went in after the wiring was completed, I imagine I must have decided at the time that access to those particular sockets could happily be sacrificed in the name of storage and then I went on to forget about them. But why the trailing ends in the loft aren't labelled I've no idea.

So - a lot of shifting or a cheap cable tracer. I'm grateful for the information about the latter.

[Andy Burns]

Worth taking the faceplates off the ones that are visible/reachable, to see if they've doubled-up cables to any of them?

[Bert Coules]

Interesting thought, thanks, and a lot less effort than shifting books, CDs, DVDs and the like.

Is that doubling-up something that's likely to have happened? I could understand it if double-socket faceplates were planned but if they were, why not fit then?

[ARW]

If it was that simple you could get Brian's guide dog to do it.

[John Rumm]

The datacomms versions are not that good at finding buried cable - but very good at identifying which cable out of a bunch of 50 you are looking for.

The ones designed for electrical circuit tracing have more range.

[Dave W]

Is there any resistance or capacitance between the cores in the "data cables"? Or between core and earth?

I made up my own tone detection system for finding the ends of a broken hearing loop round a hall. I was able to disconnect the cable from anything except my 3kHz 30Vrms generator, which I could hear in high impedance headphones connected to foil sheets held near the cable run.

Unfortunately when I went back the following month to connect the two ends with a length of wire, a new loop had been installed with a crummy amplifier and useless directional lapel mike,