Buried conduit for fiber

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 Question by Tom Schaner posted 20 May 2005
 Buried conduit for fiber
I am excited to see what your web site has to offer. I have a commercial installation question for South Florida. There is an existing 1-1/2" conduit with a 50 pair and pull string. The 50 pair is being abandoned. We hesitate to use this pipe run in fear of dirt, water etc in the pipe. They have had problems with it. Our proposal is to install 1-1/4 PVC sched 40 along the same path. Our client is supplying the fiber. At this point all I know is it is suitable for direct burial, I'm guessing one 12 strand. The PVC is for protection as well as providing a pathway for future growth. At what depth do we need to cover the conduit? Just curious if it was installed direct bury, what depth would that be? Length is approx 475 ft relatively straight run, maybe a couple 45 bends not sure. Are 45's OK or do you suggest sweeping bends? I forget what the total degree of bends allowed before you need a pull box? (180??) Thanks for your help. Keep up the good work!
 Answer by Joseph Golan posted 25 May 2005
Dear Tom,
First, Is the old conduit unserviceable? You can save a lot of money reusing this even if the 50 pair cable is shot?

Even your new conduit, no matter how well it is installed, will not be water-proof, use a proper outside plant cable with water-proofing compounds should give you many years of service.

You should by all means contact the Authority Having Jurisdiction (AHJ) for any local codes and requirement covering this installation. Only they have the last word of what is allowed and acceptable.

In general:
Buried cables should be at a depth of 24-30 inches depending on the load above.

Your bend radius should not exceed 10 times the diameter of the conduit.

Pull boxes should be installed every 180 degrees of bends.

Joseph Golan, RCDD

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