Help me win the lace race.
April 15, 2009 7:13 AM   Subscribe

I have become fascinated with cable lacing in lieu of zip-ties. I want to do it in a plenum ceiling, but I read that's a no-no...

..because of the materials. I'm using plenum-rated Cat-5e and I'm smitten with the idea of a long running lockstitch. Call it romantic geekiness or something. But the waxed twine/ribbon you can buy from various supply houses don't say anything about being plenum-rated, and I've read (somewhere) that cable lacing isn't meant for plenum areas.. how true is this? I'm in the US.

For the extra bonus pretzel, how is the lacing needle used? I can't find instructions anywhere.

Thanks very much.
posted by ostranenie to Computers & Internet (8 answers total) 4 users marked this as a favorite
One of the things about plenum cable is the insulation and jacket is a fire-retardant material that isn't supposed to support combustion on its own. Waxed twine is pretty good at burning so you really don't want that in a plenum space.
posted by FishBike at 7:36 AM on April 15, 2009

Response by poster: What about some kind of flame-retardant thread/twine/ribbon? Do they sell that anywhere that's specifically for plenum ceilings?
posted by ostranenie at 7:45 AM on April 15, 2009

I don't know what makes some thing acceptable in a plenum space, but cotton string does not burn well. It chars but does not carry fire.
posted by d4nj450n at 8:09 AM on April 15, 2009

Best answer: Does your plenum space carry return air to your HVAC system? The thing with plenum grade wiring is that it does not release toxic fumes when it burns, so you don't get fumes being returned to your system and pumped back out through your vents.

If you don't have return air going through the plenum, you don't need to worry about it.

If you do, then anything that isn't toxic will be safe to use.
posted by orme at 8:43 AM on April 15, 2009

Response by poster: I've used the Velcro spool and it's great. I'm probably going with cotton thread here since it's worked great on my test bundles. Thanks for the answers!
posted by ostranenie at 9:18 AM on April 15, 2009

I really love cable lacing too, and have long wanted to find some application to use it, but I really question whether it's a good idea to use "just because." Yeah, it's really cool, but there are reasons why it's uncommon: Velcro ties are easier to use and make reconfiguration a lot easier down the road, and require less time to install. Even if you don't care about the installation time, laced cable assemblies can be a real PITA to modify after the fact. (If you're anything like me, you'll probably just end up zip-tying stuff to the outside of the bundle, which is messy.)

Cable lacing is really a technique best left for when you are putting together wiring harnesses for a specific piece of equipment, similar to what's shown in the link's images. If you were dead sure that you wouldn't need to reconfigure it anytime soon, you could even use it to wire up a rack. (I've done it for my analog audio equipment racks, since I don't think I'll be taking them apart in the next 10+ years. I wouldn't do it for servers, though.)

Lacing is really ideal for when you want a neat, tight assembly in a densely-wired environment; I don't think it's advantageous on a long run of cable, like you'd get going from a patchbay to outlets in a building. Unlike zip ties or Velcro, where you can just use them as needed, laced cable always uses at least as much lacing as the wire run: that's pretty inefficient in a well-supported horizontal run where you really only need to bundle the cables in a few places. (And if you're finding yourself needing to keep the cables tightly bundled throughout the whole run, I'd say it's probably a sign that you need to support the cables better, with cable hangers or similar. If you're on a budget and can't afford real cable hangers, I have found that the plastic "j-hook" hangers used to support sewer pipe work well and are very inexpensive. If you go to a plumbing supply company you can buy enough to nail one to each stud along your run, and then just let the cables sit in them. Very easy to reconfigure later, and no worries about crushing your cables. And most of them are already approved for installation in plenums/walls.)
posted by Kadin2048 at 10:38 AM on April 15, 2009

Western Filament sells lacing tape that's rated to 800F.
posted by mrbill at 12:54 PM on April 15, 2009

Cable lacing is a black art and done properly, a thing of beauty. I learned to do it once a long time ago in some telcom closets, and it's actually relatively straightforward, though I couldn't do it again if you held a gun to my head.

One of the nice things about cable lacing is that it allows the cable to more or less support its own weight - this is especially important if the runs are along a wall where it may not be feasible to mount multiple support points.

It's also really good for keeping things nice and neat when running in ladder rack.

Decades ago, in Central Offices (where the practice is common) inspectors would test tension on a lace job with a spring-loaded tension thingy, and if they were out of spec, they'd snip it and have the cabler re-lace.
posted by Thistledown at 3:31 PM on April 15, 2009

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