Q

When designing a FTTH GPON project, is it possible to use many cables in the same conduit, or must I

Fiber expert David Hashman lays out the options available for fiber to the home gigabit passive optical network project designers when it comes to placing cables in conduits.

I'm designing a fiber to the home (FTTH) gigabit passive optical network (GPON) project. Is it possible to use many cables in the same conduit (e.g., four core cables for an end user), or must I use subconduits?

Yes, it is possible to run multiple cables in the same conduit without subconduits or innerduct, although this practice tends to be more common in building environments than in outside plant construction. The biggest reason for using subconduits or innerduct is to avoid the risk of damaging existing plant when adding or removing cables later. This is not normally a major risk for FTTH deployments, since they aren't usually faced with...

a lot of moves, adds or changes in their fiber infrastructure.

The factors to consider are:

  • The size of the cables
  • The size of the conduit
  • The length of the run
  • The number of bends in the run
  • The fiber installation technique (pulling, blowing, etc.), and
  • Whether the cables will be installed individually or all at the same time.

The main issue is to never exceed the maximum pulling tension for the cable. This is particularly important for fiber. Pulling lubricants can help with this, along with increasing the size of the conduit. You should always consult with your cable's manufacturer to determine the maximum recommended tension for single and multiple cable pulls.

If you are primarily concerned with running multiple drop cables to a premise, however, this is rarely a problem. Drop cables -- especially the flat ones with dual strength members -- are very sturdy and the drop distances tend to be relatively short and straight. Another option you may wish to consider, depending on your application, is the use of higher fiber count drop or backbone cables to reduce the physical number of cables required.

This was first published in July 2010

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