Inter-buildind Raceway Question FREE cabling and networking Helpdesk
 Question by Matt Bosley posted 09 Apr 2005
 Inter-buildind Raceway Question
I have an outside conduit installation question. I am a low-voltage electrician. Where I work, management would like to install a supplemental fiber cable between two buildings. Burial is not an option. There is already an existing fiber cable inside a 4 PVC raceway attached to a concrete wall that runs from building to building. There is an interduct inside the PVC with one fiber cable, and a 100 pair telephone cable. The existing PVC has six or seven 90 bends without a pull box. I am hesitant to try to pull another interduct through the PVC.

The installation will be a southern exposure, subject to expansion and contraction problems. For cost, PVC would be the cheapest and easiest to install; I'm suggesting installing a dedicated metallic raceway (EMT or rigid) parallel to the existing PVC with appropriately spaced pull boxes. Management wants PVC, may approve EMT, and would freak at the cost of rigid. The raceway I want to suggest would be 1 1/4 or 1 1/2-inch EMT with TX type expansion couplings. As the raceway will be dedicated to this one fiber pull, I don't think we need interduct in the raceway, only sleeving it at each end. The fiber to be used is something they have laying around, suitable for a damp location.

Article 770-6 says fiber can be in any raceway approved in chapter 3, so I feel I am OK code-wise.

Any comments or suggestions would be appreciated.

 Answer by Joseph Golan posted 09 Apr 2005
Dear Matt,
I see no problem with what you are proposing but they make expansion joints for PVC as well. You do not state what the lengths are that may justify expansion joints nor the size of the fiber. If your fiber OD is small enough, you may want to consider using a small innerduct (3/4" )in the existing 4" conduit and save yourself a load of work with the new pipe run, just a thought.

Joseph Golan, RCDD

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