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Are there any devices that allow you to basically clip a wire to an existing wire in a wall and use it as a guide? I had my house wired for networking, but that was before I upgraded to gigabit fiber. I want to run the CAT6 cable from the fiber box up into my garage ceiling over to my network rack across the garage, but not sure how to do it. I've got access to the holes the installer used to run the cable the first time, and I can easily get from the modem to the existing wires, but I don't want to have to re-pull cable from my upstairs just to pull this cable through. I thought about trying to use an existing wire as a guide, and fish new cable through, but only way i could think of that is to use maybea paperclip or something to attach to an existing wire, then use fiberglass rods to push the new cable along the path of the old one.

Is there an easier way to do this without using one wire to pull new wire through?

Edit: Maybe I wasn't clear enough. I don't have pictures at the moment, but I'm not trying to run new cable to existing outlets, I'm trying to using an existing cable (lets not call it ethernet, lets say it's a power cable or telelphone or coax or something to make it easier) as a guide for a different cable.

I have a 3 story house (garage, 1st, 2nd). In one corner of my garage is a small 6U cabinet with router, core house switch, UPS. In the other corner of my garage near my utility panel is my Fiber gateway from ATT. Currently I have a cable strung along the ceiling running from the gateway to the 6U rack. I want to run this up through the garage ceiling and back down... but it's about 20FT away, through insulation. In the middle of my garage, i have a small access hole my network installer used to help run the CAT6 cable from 1st and 2nd floors to the garage. From this hole I can easily go about 8FT to where the gateway is, and another 18-20 ft to where the 6U rack is. I basically want to thread new cable up into the ceiling from the modem, pull it over to where the bundle of other cables from 1st and 2nd floor come, and then join it to where the rack is. I thought about undoing one of the 1st floor cables and using that, but that would mean pulling/terminating new cable to the first floor, just to act as a guide in the garage ceiling. I was hoping for a tool or something to basically hook in at the ceiling hole, and then "push" along an existing wire to run the new garage line.

If pulling existing cable is the only viable option, I guess that's what it'll have to be, just trying not to yank anything existing out if I don't have to.

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    Do you plan to continue the old wire in service? Or is it junk?
    – Harper - Reinstate Monica
    Sep 5, 2018 at 22:10
  • yea i want all existing wires to stay in service, I'm just trying to feed a new cable in the garage along existing wires coming from 1st and 2nd floor
    – Evan R.
    Sep 6, 2018 at 22:40

3 Answers 3

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Fish Tape

A real (and "reel") fish tape is often the tool to use. Because it is flexible and very long (typically 25' or 50'), you can get a lot farther than just fiberglass rods. But it can be a pain to use, depending on the path.

Tape to old, pull new, pull back old

When you have (as I think you do) an existing cable that you want to keep and want to run a new cable in the same path:

  • Disconnect one end of the old cable
  • Tape the new cable to the old cable. Any strong tape (both tearing strength and adhesive strength) will do - the stronger the better.
  • Use the old cable to pull the new cable through to the destination.
  • Untape the new cable and pull through an additional complete length - i.e., the same length as you had to pull the first time.
  • Tape the middle of the new cable - which is a location that will become the starting point - to the end of the old cable.
  • Pull the new cable back down. You will now have the old & new cables in the right place.

If you think you will ever need to do this again - e.g., another parallel cable or a future upgrade - then instead of using one cable to pull another, use pull string:

  • Disconnect one end of the old cable
  • Tape the pull string to the old cable. Any strong tape (both tearing strength and adhesive strength) will do - the stronger the better.
  • Use the old cable to pull the pull string through to the destination.
  • Untape the pull string and pull through an additional complete length - i.e., the same length as you had to pull the first time.
  • Tape the middle of the pull string - which is a location that will become the starting point - to the end of the old cable.
  • Pull the pull string back down. The old cable will now be back in place.
  • Disconnect the pull string from the old cable.
  • Attach the end of the new cable to the pull string.
  • Pull the new cable through to the destination.
  • Cut the pull string and tie it up in the junction box or other accessible (but hidden is OK) location at both ends.

You now have a pull string that you can use the next time. To use it again, tie a new section of pull string to the old pull string and tape a new cable as well. After pulling through cut off the extra pull string and tie in place for the next time.

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    If you use the old cable to pull the new cable, make sure you tape them together in a way that's unlikely to snag on obstacles, and strong enough that you can pull hard on it without breaking the connection. One way is to lay the cables so the ends overlap by about a foot, tape the overlapping section together, then continue to tape past the overlap a bit so the tape creates a smooth taper from the two cable section to the single cable section.
    – mrog
    Sep 5, 2018 at 22:42
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    A strong connection is sometimes not enough - I've had a Cat 5e break in mid-pull. That was really not fun.
    – Eli Iser
    Sep 6, 2018 at 0:43
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    @EliIser Been there, done that. And had the end of a fish tape catch on holes in steel studs. And plenty of other mishaps. Cabling is not my favorite activity, but I do it when I have to.
    – manassehkatz-Moving 2 Codidact
    Sep 6, 2018 at 1:54
  • this might work actually.. sorry I missread your 2nd point as pull new cable through, but you're saying pull one way, then pull back again.
    – Evan R.
    Sep 6, 2018 at 21:38
  • I'll try using fish tape first to see if that is stiff enough, if not looks like I'm buying a new spool of cat 6.. maybe only 500ft instead of 1000
    – Evan R.
    Sep 6, 2018 at 21:38
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I just strip a few inches of the outer jacket off then twist the ends together then a couple wraps of tape and pull through most com cables are not stapled but if they are a fiberglass rod is the easiest way to go from an attic or crawl space down through the wall, I use glow rods as the glow and are easier to see in the dark cavity, trying to run fish tape is fine for conduit but in a wall the tend to coil up that's why I use fiberglass rods.

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  • I recently had an electrician run many network cables in my home, and they seemed to do it the same way as you: tape the ends together and use rods to move the cable around and pull it through the holes they drilled. Almost all the runs were through unfinished areas, so I don't think they even needed to use fish tape at all. Also interesting is that they used a 3 foot plastic drill bit to scout out paths between floors before they drilled larger holes.
    – Kaypro II
    Oct 14, 2018 at 15:59
  • Being an electrician my self this is the way we do it in walls.
    – Ed Beal
    Oct 14, 2018 at 19:17
  • Always pull a new draw cord in with the new cables - future-you will be grateful.
    – Criggie
    Nov 5, 2020 at 1:36
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Why not just use a female-to-female RJ45 connector to join the old cable to the new cable, and pull the new cable through?enter image description here

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    As Eli Iser noted, there are sometimes problems that prevent a smooth & easy pull. Even if this were across a known open area (e.g., drop ceiling), I'd be skeptical about the connectors holding the cables together long enough to get the job done.
    – manassehkatz-Moving 2 Codidact
    Sep 6, 2018 at 1:53
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    Actually another bigger problem. If done (IMHO) right, the old (and new) cables should be from jack to jack, NOT from plug to plug. Terminating long through-wall/ceiling cables with RJ45 plugs is not a good idea because the plugs can - and do - break after repeated insertion cycles. The jacks almost never break.
    – manassehkatz-Moving 2 Codidact
    Sep 6, 2018 at 3:16
  • can't use one of those. Imagine it like this. I have cable in my garage ceiling, that goes to the 2nd floor of my house, to jacks in the bedrooms. I basically want to run cable up from a new spot in the garage, join the other cables, and run it to the back of the garage where the rack is, but there's a ton of insulation in the ceiling, so visually lining it up will be hard. Without pulling the cable out from the 2nd floor back down through the first floor to the garage is what im trying to accomplish.
    – Evan R.
    Sep 6, 2018 at 21:29
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    That'll snag on everything. And it has very little pull strength (plug to socket or wires to plug so it'll likely just break off.
    – Harper - Reinstate Monica
    Sep 6, 2018 at 22:48

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