Pulling old cables from conduit OR 'the tale of the improvised tugger.'

General Questions
#1

Its fall and time for a little house-cleaning at work, so I decided to tackle the long-standing issue of old, unused cables left behind from older control systems in our lecture halls. There are several cables, including some RG-59 coax, and a few pieces of 24-conductor twisted pair, all stuffed into a 2" pipe. The pipe goes into the floor, straight down, takes a sharp turn, runs under the floor, and pops back up through the floor in another room. The run is maybe 100 feet, and since we’re on the ground floor, the pipe is embedded in concrete. To the best of anyones knowledge, there are no junction boxes, its just a continuous piece of pipe. The cables in it have been there for at least 30 years, maybe longer.

The first order of business is to pull like hell. I try this a few times, with no luck. Clearly something stronger is called for. Real electricians use something called a ‘cable puller,’ also known as a ‘tugger’. Now I don’t have one of these, but I do have access to any number of devices for amplifying human effort. After considering, and abandoning, a number of ideas (including using a come-along mounted on a sawhorse) I settle on a simple 2-ton engine crane. I wheel the crane over the pipe, lower it, tie a piece of coax onto the hook, and start pumping. The crane boom rises; tension on the cable increases. Pumping the hydraulics gets harder. Soon the boom starts to flex a bit. I keep pumping, and suddenly the system goes slack. But it turns out I HAVEN’T pulled the cable part way out of the pipe. Rather, the coax has simply snapped under the force: insulation, braid, conductor, dielectric and all.

So my question to the assembled minds of the Dope is: what the hell do I do now? I mean, if the amount of force required to SNAP the cable isn’t enough to dislodge it from the pipe, what else can I try? It SHOULDN’T be in there this tightly; I can only imagine that over the last 30 years the insulation on the cables have degraded to the point where they are welded in place. Is there anything that can be done to loosen them up? I could try pulling on the twisted-pair, its probably stronger than the coax. I’m hoping that if I can get one cable free, the others will come out more easily.

#2

And yes, before you ask, the other end of the cable is free.

#3

Ummm, fill the conduit with cable lube?

I’m not sure if it would work. I’m only offering it up for an electrician to comment about.

#4

Gonna bet that any cable lube used for the original pull has evaporated, or changed state*. The insulation is no longer as flexible as it was three decades ago. In short, I think you’re hosed.

*Yes, it’s still in MD, but is acting more gluey than slippy.

#5

Do you need to remove only a couple selected cables, or are you tring to clean out the conduit entirely?

At this point, it probably doesn’t matter, as there’s a good chance you’ve damaged other cables with the engine hoist attempt. The technical term for this is “sucks to be you.” :stuck_out_tongue:

About all you can do is try pulling from the other end a bit to see if you can free things up - this is roughly analagous to “rocking” a car that’s stuck in the snow.

Last-ditch effort is to introduce some water, hoping to re-constitute the wire lube that had to be needed to coerce all of that wire into the conduit. If you’re lucky, it won’t all dribble out at the first joint. (It might be a direct run, but it’s made of 10-foot segments.)

#6

I agree with gotpasswords’ assessment of the situation. Sucks to be you.
I also agree with putting water into the conduit (as long as you know there are no live wires). I would go a step further and add liquid soap to the water. Two reasons, first it might help loosen up the cable lubricant that has hardened, and secondly, the soap itself is a bit of a lubricant.
Also try pulling the other cables first, coax is strong but stiff.
Good luck

#7

Agreed that you’re probably hosed. However, I take it that you initially tied onto a single wire? That a single wire wouldn’t come free doesn’t surprise me. Numerous wires in a single largish conduit frequently end up wound around each other to some extent, resulting in greater friction along their entire length. If you tape up all the ends into a single snake and pull the whole lot at once you are likely to have much better luck. It can also help to have someone push the tail end, or at least guide it into the conduit at the far end. If you need to be leaving some of the lines in, well, I don’t see much hope for you.

#8

If you are only trying to pull out specific lines your screwed. Do you need the conduit for another purpose?

If they all need to come out you can keep going with your method and try to break all of them. Hopefully you are getting them to break at the first elbow. Then try pulling them the other way.

Pulling all of them at once probably will not work well but what Gorsnak has to say is true. I would try moving up to 3 or 4 wires at a time that way you can apply more force without breaking the wire.

On a 100 foot run of low voltage cables I wouldn’t expect them to have needed cable lube. But you could try the soap and water and see if it helps.

As an electrician, first I would use the the brute force method. If that didn’t work Fuck that conduit. Cut it out(well the sub ups anyway) and run a new one. Preferable through the ceiling, but if we had to go through the floor so be it.

#9

I am trying to remove all of the cables from the pipe, so no worries about damaging them. Its not really something I need to do, its just something I want to do, in part to keep the floor pocket where the pipe terminates nice and clean. I thought about gotpasswords suggestion of pulling from the other end, too, but one end is in the middle of a big, open room; the other end is in a small cramped cage full of electronics. Also, since I wasn’t clear in my OP: I was not pulling on a single cable, but all five pieces of coax bundled together. They all snapped together. Not at the bend in the pipe, either, but just in mid-air. I’ve still got a few feet of cable coming out of the floor.

#10

I learned once the hard way (read: at the expense of a clutch) that you don’t get a car out of the mud by putting it in gear and flooring it: you rock it. Have you considered getting 2 methods of wire extraction going (you’ve got one already, just get a come-along or something less bulky in the other room) and alternating between them? Not actually trying to pull the wires out, but just trying to free them up some?

#11

Then Plan <counts on fingers> F or so is to just take some clippers and snip the cables off at the end of the conduit where it enters the pocket and call it a day. Is there any chance it will be your problem in the future that there’s a conduit full of jammed abandoned cable?

At least you didn’t do any structural damage to the building with that engine hoist. I’ve seen what can happen when someone uses too much force pulling wire - the wires kinked up and they just kept the motor running on the puller. Eventually something gave way, but it wasn’t the wire. They wound up replacing a bunch of bent conduit and unistrut hangers. :eek:

#12

  1. Cut the pipes off at floor level then grind them down a further inch.
    Patch the concrete.

  2. Double check that it is the same run. Send a signal through a wire and check for that signal in the other room’s wires. You could of pulled on still connected wiring.

  3. Eliminate the two ninety degree bends. This requires renting a jackhammer.

  4. Lots and lots of nitric acid.

#13

Here’s another angle-rig a fan to direct warm air down into the conduit. Verify air output at the other end. Once arranged, let it be for a day. This will make the hardened insulation jackets more flexible, and hopefully assist with your removal project.