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UPDATE: I have tried to snake 20 foot 1 inch PVC, however it is not rigid enough and suffers the same problem as the fiberglass rod

UPDATE: This space is between the ground-floor ceiling and the first floor: the wood panel is the floor of the upper floor.

There are wood trusses that run horizontally (obscured by insulation) that block if the ethernet is not high enough to clear the truss.

enter image description here

The goal is to pull CAT5 Ethernet lines through a 40 foot horizontal plenum between the first and second floor. One end of the plenum is accessible from the attic. The other end is more difficult to access. Assume worksite is at the attic end.

I have attempted to snake a fiberglass wire-runner rod. The rod is too flexible is getting caught on truss chords. If I could somehow shoot a projectile (like a crossbow bolt) with a fishing line through 40 feet of air to the other end (plywood stop) that would allow the wire to be pulled. This seems a bit overkill, however, when I am in the very hot attic, wagging the fiberglass-rod and gettin nowhere, the projectile does not seem as silly.

Is there a clever way to traverse either the rod or fishing line through the 40 ft of plenum? Removing / drilling the ceiling is not an option for this exercise.

gatorback
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  • Is plenum vertical or horizontal? Where are the rafters in the plenum? – crip659 Feb 18 '23 at 14:35
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    Got pics or sketch? For a similar situation I used lengths of PVC conduit. Stick one piece of conduit in, then attach the next (tape together if necessary). If still too flexible, you could make a wedge tip to help it skate across joists. (Or do you really mean rafters? Can't imagine how those would be a problem.) – Huesmann Feb 18 '23 at 14:50
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    Some fish rods offer an accessory that is designed to ride over obstacles. The orange piece in this kit, a whisk, is typical. Sliding across the tops of the rafters it shouldn't sag to the point that it won't ride over the next rafter. Have a look with for fish rod whisk, or fashion something similar out of materials on hand. Running the rod through a small plastic water bottle and pushing it cap end first may suffice. – HABO Feb 18 '23 at 15:56
  • Are you running across the floor trusses or parallel to them? Your rod seems to be lined up diagonally to them. – Ecnerwal Feb 18 '23 at 16:48
  • What is the access on the other end? Can a rod also be fished from there (even if you can’t get in to see)? – red_menace Feb 18 '23 at 17:38
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    Get a 2-liter soda bottle. Cut the top half off, and cut the top part with the threads off, leaving you with a bullet-ish shape. Fasten that to the tip of your PVC pipe (might need to pack the space inside the bottle to keep it from flopping). Hopefully as it encounters obstacles, the bullet shape will push the tip over them. – Huesmann Feb 18 '23 at 21:40
  • Aside - A penum is an airspace used as part of a ventillation system. As such it wouldn't have insulation visible. This looks like a void space, so the cable you install doesn't need to be plenum-rated. – Criggie Feb 18 '23 at 23:35
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    hint: strong magnet on floor above – jsotola Feb 19 '23 at 03:58
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    @gatorback if you have access at both ends of the run, then you have two 20 foot spaces to reach across, not a single 40 foot space. Then the challenge changes a bit, to add hooking the end of the first pole with the second pole. – Criggie Feb 19 '23 at 10:29
  • Are there any convenient light fittings in the ceiling below that can be removed to provide an access spot ? – Criggie Feb 19 '23 at 18:26
  • Unfortunately, there are no light fitting to provide access – gatorback Feb 20 '23 at 18:17
  • OP, did you ever indicate whether the line needs to run parallel to the joists, or perpendicular? – Huesmann Feb 21 '23 at 13:29
  • @Huesmann There are perpendicular joists: the fiberglass-rods droop and are blocked by these joists, despite attempts to wiggle / shake the rods, I am unable to get the rods to the 40 ft mark. Hopefully a pulling line gun will prevail. – gatorback Feb 21 '23 at 22:10

6 Answers6

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Fashion a stiff wire into a zig-zag shape and attach it to the leading end of your fish rods. If you're handy with a welder you could do this fancy-like by welding the wire to a screw or coupler nut so that it can be threaded onto the end of the rod; otherwise, just use electrical tape and attach to the side of the first rod.

The leading end of the zig-zag only needs to be an inch or so long. The height of the zig-zag should be 20-50% taller than whatever obstacle you need the fish rod to climb over. The tail portion can be short if you're welding it, but if taping, make it 4-5 inches long so there's lots surface area for the tape to adhere on.

Finally -- push the first piece of fish rod with this zig-zag standing up. Continue feeding more rods. When the zig-zag reaches the obstacle its ramp may just help the fish rod climb up and over. At 40 feet out, though, it's more likely the fish rod will flex instead. In this case you can rotate the fish rod -- the zig-zag should help lift the rod over the obstacle. Usually I rotate clockwise so that the screw joints in the fish rod sections all stay snug, but sometimes counter-clockwise is helpful.

At this distance it gets difficult to ensure the zig-zag is not getting itself into trouble, snagging wires, insulation, and framing along the way. A wireless or long-wire USB borescope taped near the leading end of the fish rods gives a close-up view that is tremendously helpful in navigating these challenges.

Greg Hill
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The search suggested (pulling line gun) is an available product. I don't own one and don't feel the lack of it, and I pull cables as part of my job. I suppose if you really wanted to use a crossbow you could adapt one to the purpose.

What I actually do is use a much stiffer rod (old chimney brush sectional rod) that does not flop into gaps. Bump it over 3 feet, screw on another section, bump it over 3 feet.

Without buying anything new, you might be able to use your rod with a bit more skill (thus, practice) at giving it a wavy motion to pick the end up and then shoving at the appropriate time when the tip is up, not jammed. It is rather thinner than the one I use for that job, however.

If running parallel to the trusses, some folks do use remote control toys on treads or big wheels to get a line across a ceiling; that would appear hopeless in this bay, but the bay to the left appears more open. Those cost a lot less than a line gun, on a quick look.

Ecnerwal
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    I’ve also used 3/8" or 1/2" PVC (taping the sections together, just sayin’) - that’s also cheaper when your apprentices lose them. – red_menace Feb 18 '23 at 17:07
  • Please consider posting a link to the stiffer rod that you use?

    Thank you for the "pulling line gun" suggestion. It's pricey at $400, however, if that's what it takes, then it is what it is. If only I was accurate with a "Dennis the Menace" slingshot :)

     – gatorback Feb 18 '23 at 17:18
  • Look for chimney brush sectional rod. I'm quite sure mine predates the internet. 3/8" fiberglass with screw connections between sections. – Ecnerwal Feb 18 '23 at 17:23
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I've seen a low-end crossbow modified with a fishing reel used for exactly this purpose. The monofilament was attached to a custom made bolt (arrow) and free-spooled out when the unit was fired.

It was also designed so the bolt could be wound back with minimal risk of snagging - the whole bolt was tapered and smooth with no projections, and the fins were equally smooth in both directions.

My uncle used it for casting lines through a ceiling space just like this, then pulling back a soft woven draw cord which was tied in a large loop back under the ceiling. Cabling was pulled through using this longer loop, and being tied there was no risk of it being lost.

At the end of the job, pull in a couple of bright orange nylon cords and staple/tie them clearly visible but out of the way, so a future person can use them.

Criggie
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    Hmm, a crossbow. I knew a guy who used a slingshot, with a hardware nut and fishing line. He also used remote controlled toy tractors to pull fishing line. – Wastrel Feb 19 '23 at 16:58
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    I've heard of a longbow being used (at the NEC in Birmingham UK) to get lines over roof trusses. – Mark Morgan Lloyd Feb 19 '23 at 17:59
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Temporarily disconnect something else

What other cables go in the same direction as you need? That yellow one looks to be a possible candidate.

Find something you can temporarily disconnect. Try and see if its been cable-tied or stapled or nailed down, and if its free to move then disconnect at one end.

Attach a couple of draw strings and gently pull it back to the other end.

Attach your new cables along with the temporarily removed cable and pull them all back in with the draw string. Don't be tempted to shortcut and use the temporary-disconnected wire as a draw wire.

When you're done, aim to leave at least one draw string in place for the next guy. And reconnect the temporary one too, in a proper workmanlike manner.

Criggie
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This is 2023: there's any number of small, light radio-controlled tanks and rovers with a camera for navigation which could easily traverse that insulation pulling a thin nylon line.

Mark Morgan Lloyd
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    Great idea if the ground were flat, but OP's pic shows insulation, which is probably covering purlins for the ceiling below and would be hard to cross. – Criggie Feb 19 '23 at 18:25
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    I wouldn't expect insulation to give something with tracks any problem: the photo doesn't show any particular quantity of loose fibre being shed. A rover (e.g. with a rocker-bogie as used on Mars etc.) might have a bit more difficulty... it really all depends on the tradeoff between contact area and the distance of the moving parts from the fibre surface. – Mark Morgan Lloyd Feb 19 '23 at 18:30
  • Drone racing. First one through wins the tofu. – HABO Feb 20 '23 at 15:51
  • Of course, that's presuming one can find one small enough to fit through all the little areas, yet sturdy enough to make it over the big humps in the way... – FreeMan Feb 21 '23 at 17:46
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Use a cone

Add a plastic (or heavy paper) cone to the end of your pole. This can get tricky because the overall diameter needs to be able to squeeze through the smallest diameter you need to go through but larger that twice the size of any obstacle you need to lift over.

In two dimensions you are going for this. -------->

This way assuming that the height of the obstacle you are going over is less than half the diameter of the cone, the cone will rise up and over the obstacle. Basically the cone keeps the tip from running along the ground.

I've used plastic placemats from Ikea for this but heavy card stock would probably also work.

Ideally the cone should not be extreamly stiff as then you will be able to push it past any tight spots.

Justin Ohms
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