August 21, 2003  ·  Lessig

So a bunch of people in San Francisco (with Brewster Kahle, who’s behind all great ideas behind it) are building a free wireless network for the city, called sflan. My wife’s and my house is to be sflan16, and last weekend the team came to the house to install the antenna.

Our house has just undergone major renovations (a 9 month project which is 6 months late; the other 9 month project is humming along just fine with eta 2 weeks), and we included in those renovations a conduit from the roof to a server room in the basement.

But when we tried to run the Ethernet cable from the roof to the basement, we discovered that the conduit makes 3 90-degree turns and one 45-degree turn, and it was not at all clear how one pushes a cable through such a maze.

So of course we turned first to the internet. I typed in a totally natural language question into Google (which I find these days is increasingly the best method): something like “how do you thread a cable through a long conduit with 90 degree angles.” The first post that came up was a thread from some list titled Threading fiber through a long conduit. This thread reported no good luck, but it had the kernel of an idea: a vacuum cleaner.

So we took a bit of foam, tied it to the end of a roll of kite string, and connected a small Shop-Vac at the other end of the conduit (which is at least 50 feet long). Bingo. The key, it seems, is to have a big but light obstruction, and google at hand.

  • Brian

    I will have to remember that little trick.

  • lessig

    no need to remember. just google it!

  • steve

    Of course you might use a ferret, but they are illegal in California.

    (the Swiss PTO used to use them and I have used ours in ferret-friendly NJ for short runs)

  • Brian

    True, but if Im pulling cables I may not have a net connection. :-)

  • lessig

    unfortunately, a ferret wouldn’t have fit our 1″ conduit. Maybe a cockroach…

  • Drew Vogel

    Once I had to run a set of wires through a horizontal pipe which formed three sides of a square. I clamped a magnet to one end, then pulled it through with a cow magnet.

  • adamsj

    Dang, Larry, can you teach me this trick?

    “My wife and my house is to be sflan16.”

    That’s very public spirited of her, but doesn’t it limit her mobility?

  • Richard Bennett

    Clever trick, that foam deal – reminds me of the “pig” they use at the Monterey Bay Aquarium to keep their water pipes free of barnacles. Another method uses a ping-pong ball, but it won’t fit through all conduit and you wouldn’t want to get it struck. If you can’t thread your Ethernet wire through the conduit, you can use flame-resistant UTP running alongside the conduit. In the fullness of time, you’ll want to replace your UTP with optical fiber, but that’s going to be a snap now that you’ve got a good strong wire to pull it with.

    When Williams converted some of their oil pipelines to an optical communications network, they build a little robot to pull the fiber through it; some others have used animal companions, I believe.

  • Evan

    Why that sflan idea is just beautiful. How does it work? Who pays for the bandwidth and hardware and whatnot, and how is it organized? The website you linked to is skimpy on the details.

    If I still lived in SF I’d love to help out. I’m wondering what it would take to do the same thing in Santa Cruz.

  • Brian

    Here is a link to an article in the Washington Post that talkes about WIPO and Open Source. How a meeting on Open Source in the IP Community should be talked about but was seemingly squashed by the big players (BSA, Microsoft …) I don’t know why it didnt occur to me before but I finally see a direct corelation between the MPAA/RIAA vs P2P Trading and Closed Source vs Open Source. Both Capitalistic structures are being attacked by business models they can’t comprehend. I think a lot of the closed source community is still in shock/awe that the Open Source community really works. The Open Source community isn’t in it for the money and that just blows them away.

  • janne

    We wired our neighbourhood some years ago. We didn’t use foam, but instead we got good, strong yarn, which is pulled along just beautifully by a vacuum cleaner.

    If there already is cable of some sort in the conduit, you can unhook it, tie the new cable, and a pullstring to it, and use it to get the cable through. Then you use the wire to get the original cable back into place. We used this trick for the last stretch into each apartment, as we went through the telephone conduits.

  • Scott Leverenz

    My night, I’m a meek and mild computer geek, by day, a heating and cooling contractor. In our business we need to run thermostat wire through many mazes as you describe. Most of the time, with out benefit of a conduit. We use a tool called a “fish tape” for fishing wire through small holes we’ve drilled to get the stat wire to where we want the thermostat to be. Some of the techs have 50′ tapes, some 100; foot tapes. Search google for ‘fish tape’ and you’ll find them.

    I must say I admire the creative way you came up to solve the challenge at hand. Now if I could only get my techs to think “out of the box”. Congratulations!

  • Tim Pozar

    re: SFLAN…

    SFLAN is one of two networks deploying wireless through SF. You can check out SFLAN at SFLAN was started some years ago (~’98) when Brewster heard of Bill Joy’s network in Aspen and thought it would be cool for the SF Presidio. It had about 5 access points and ran for a number of years at this level until recently when it was restarted to deploy APs throughout SF.

    SFLAN is getting some help from the network I started call the Bay Area Research Wireless Network ( where we developed the hardware that SFLAN uses and SFLAN uses some of our nodes to get bandwidth to them.

    Tim Pozar

  • mike

    I’ve found that ball chain, the kind used for pulls on ceiling fans and ceramic light sockets, works great for fishing through conduit. Just start at the top, and its own weight pulls it through. You may have to invest in a large spool of it, but it’s reusable. Also works for irregular plenum and wall cavities – provided there is a way through and enough gravity, the ball chain snake will find it!

  • bloopy

    i saw something like that on one of those “this old house” type home-improvement shows several years ago. . . instead of foam they used a partially-inflated balloon which, to me, seems like it might work out better. . .

  • lessig

    true enough, adamsj. corrected.

  • jayo

    The last time I helped in a big pull it was 1500′ of fiber from our shop to our office at work, we already had a heavy string line blown through the conduit, then we attached a small bobcat skidsteer and used that to pull while 2 other guys pushed. It was a pain but it went through.

    I usually just use an electricians snake for short runs, it will go though just about any bends 90′s, 45′s it doesn’t matter, the one I have is 75′ long (used to be 100′ but mangled it too many times and had to cut the end off).

    Also with the ball of foam idea if your vaccum doesn’t have enough suction you can use a air compressor to push the ball through. Average air compressor is 120psi, that is a lot of push, that same pressure fires spuds from my pnematic potato gun about 300yds. @ 600 f/s.

  • Joe Dorn

    One other handy thing to know about in these situations is wire pulling lubricant. It is super slippery goo that you spread all over the wires as they enter the conduit. It works real good in sticky situations!

  • Charles Franks

    Fishtape is fine for reasonably short runs but this vacuum cleaner trick is an old standby for doing really tricky runs fast. I generally use a sandwich bag or something similar on the end of the line… something with high-drag and low weight. Word of caution: the rope or string can be going into the pipe _fast_ and you might get some nice burns on your hands if you are not careful when feeding it into the pipe. You can also shoot the line if you have compressed air but no vacuum. A tampon works great as a leader for blowing string through small diameter pipes.

  • Vince

    A similar method involves vacuuming a piece of wire pulling cord -the stuff that packages are wrapped with, usually blue or pink in colour and feels waxy- and then tying your cable onto it. You can pull cable several hundreds of metres this way.

  • Wesley

    I prefer nanites myself. Place some nanites and a bit of silicon at the entrance to the conduit, and in no time, they will form themselves into a fiber for you! Almost as good as using sea sponges, but much quicker. No lubrication needed. I don’t have to use women’s products that are still hard for me to discuss in front of the Captain.

    Sure, reprogramming the things when they go askew is a bitch, but I usually find that changing the polarity on the bertold projector does the trick nicely, all by act iv!