Fiber optic cable question

I have been asked to run a fiber optic cable of about 600ft through a warehouse. There are conduit pipes overhead about 30ft high that run the length. is it possibe to lash the fiber cable to those conduits? and if so what type of cable would i use?

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zeussix wrote in part:

Well, the preferred technique is to build a cable-tray and put the fiber in it. This will win the heart of even the most black-hearted electrical inspector. So long as you bond it :)

But people run fiber along conduit all the time, and it's tough for anyone to argue so long as it isn't conductive. It's safer than pull-string.

I'd use regular indoor grade. All that I've seen have enough kevlar for strength since they're often used for riser runs in tall buildings. If you have doubts about your connectorizing ability, take the trouble to measure well and get a length custom mfg'd. Allow for plenty of slack.

That conduit is going to have supports at least every 25ft also to support the fiber (two-point tie--you don't want the cable shuffling slack lengthwise). If you're worried about the "clothesline effect" and the hanging arc being caught by moving vehicles/equipment, you can add mid-point ties. One trick I've seen used is to lift and wrap the arc two times around the midspan and tie-down. The wraps add 4 support points to the length.

-- Robert

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Robert Redelmeier

We have an entry about this in our cabling FAQ:

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Bottom line: the code says you can't strap a communications cable (I interpret is as copper or fiber) to the exterior of ANY conduit. Have I seen it done? Of course! However, much better approach would be to use the threaded rods that most likely support the conduit to install your very own J-hook line. Use brackets with clamps that let you install a hook onto existing installed rod. There will most likely be a slight problem: the hooks may be a little too far apart which may be causing too much sag. It actually depends on the size and stiffness of the cable you use. The famous "a hook every 5 feet" rule only applies to UTP copper cables and you can go further than that with fiber. However, too much sag will make the cables too insecure and will make them swing in drafts (which accelerates microbends aging of fiber) and simply they can be accidentally pulled at when someone else needs to go into the ceiling later for whatever reason. To prevent the unwanted sag (you want at least some sag 'cause you don't want much tension) you can clamp a steel messenger wire to the same rods, tighten the messenger wire and then lash the fiber cable to the messenger.

Whole another approach would be to go even higher and clamp your J-hooks directly onto the beams thus elimination messing with existing conduits altogether. I guess, this kind of install is exactly what you are trying to avoid, but in some instances it is not possible to avoid.

Oh, and another thing: you can use regular (non-plenum) grade fiber optic cable. However, to add some stiffness to the cable you can opt for non-plenum rated indoor/outdoor version. Some designs use the same type of buffered fiber inside as the indoor cables but much thicker jacket made of different plastics (plus stiffener rods in the center) that can eliminate the unwanted sag.

Good luck!

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