I am well aware that this is pushing what can be DIY-ed.

I live in a student housing cooperative, and the two houses it comprises have an unused phone network running between them. The network was run through a CAT3 50- or 100-pair cable. The cable has a steel sheath inside, so I am assuming it is a direct burial between the buildings, running between both basements and underneath the pavement beneath the two buildings. The length of the run is probably 20-30 metres, but it's hard to tell because there's no way of knowing where exactly it goes underground.

What I hope to do is pull the individual conductors out of the cable, so that I am left with an empty sheath only. This I intend to use as the conduit for several CAT5e cables to replace the obsolete CAT3 wiring.

I've tried tying the conductors to a stick and pulling really hard, which didn't quite work out. If I pull on only a few conductors at a time, say up to 8 or so, I can pull out a few millimetres worth of conductor before they break from the strain. If I pull a larger number at a time, they only come out by a few millimetres, if at all, and it may be just the insulation stretching rather than the conductors sliding through. However, the conductors are very greasy, which I'm assuming is either to make them waterproof, or was perhaps used to pull them through originally (although it's more likely that this is a direct burial cable). So it seems like I should be able to pull the individual conductors out, pull some string or wire through, and use that to pull new cables through the remaining sheath.

Is doing this feasible at all? Would using an electric winch help, for example? Has anybody done anything similar before? If I can find the mechanical specifications of the cable, could I calculate how feasible it is (based on the maximum pulling force & the length of the cable, for example?)

I understand that the professional solution would be to dig up the cable and replace it.

1 Answer 1


No, the intelligent (budget-concious) solution in this case is to use the cat3 conductors and any of various schemes to run ethernet over them; starting with the base case that 10Mbit ethernet runs happily on Cat3 wire, and many Cat3 wires are actually fine for 100 Mbit. Those are "free" solutions.

You could put trunking switches on either end and run a bunch of 10 (or 100 if you get lucky) mBit connections in parallel (there will be a lot of pairs - likely 25, so you can run up to 12 wait, you say 50 or 100, so 25-50 - only takes two pair each) for pretty cheap. Except you went and yanked on and broke the wires already.

You can get two-wire "ethernet extenders" that will happily run 40 mBit or more on a single pair. They cost a bit more, usually. Your wire abuse also lowers the odds on those, unfortunately.

Thus, the correct solution for you in this case is to ignore the wire you have been abusing and put a couple of 5 GHz Point-to-Point radios on the buildings where they have a clear line of sight between them.

Or dig a trench and install fiber optic in conduit. That certainly is the "price no object professional approach" and has the benefit of being unaffected by thunderstorms which can wreak havoc with copper inter-building connections. Digging up the old cable is not normally a part of this approach, since it just adds a headache. Calling DigSafe several days before starting is a part of it, though...

When you pull on the wires, you are probably pulling against the telco's strain relief when you snap them. Virtually all "old phone cables" were installed by Ma Bell and she didn't just dump a cable into the ground. Which is to say, yanking the wires out is not going to work.

  • Thanks very much for the comments! I wish I'd asked before pulling, but there's plenty of slack left at the end of the cable, so I can just cut the broken ends and reterminate, barring any damage further down the cable. It'll be a nightmare tracing all the individual ends and figuring out if they're still intact, but I'm willing to spend that time. You mentioned 'trunking switches' - will any old switch fit that purpose, or can you recommend any particular models? Also, re: point-to-point radios, that's what we use. I'm just trying to repurpose existing equipment that's not in use.
    – user37450
    Commented May 12, 2015 at 14:44
  • Wouldn't any strain relief measures be installed on the outside of the sheath, rather than inside the bundle of conductors? Can you point me towards anywhere I could read up on how it works?
    – user37450
    Commented May 12, 2015 at 14:46
  • Not all switches can do trunking. Most "smart" switches can; just look in the user manual for either trunk or LACP (link aggregation control protocol.) There may be limits to how many ports a given switch can put in one trunk (8 is a typical number.) The wires should be color coded for easier sorting out. If you can sort out wires you have not yanked on your odds improve somewhat - excessive pulling can damage transmission characteristics even if there is DC continuity. The strain relief will clamp the whole cable and may be located external to the building.
    – Ecnerwal
    Commented May 12, 2015 at 15:34

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