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Microducts Solution

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Microducts

Microducts are typically small-diameter, flexible, or semi-flexible ducts designed to provide clean, continuous, low-friction paths for placing optical cables that have relatively low pulling tension limits. As stated in industry requirements document Telcordia GR-3155[1] Generic Requirements for Microducts for Fiber Optic Cables, microduct products are expected to:

  • Be compatible with existing construction designs and building configurations for both riser- and plenum-rated applications, including cable blowing apparatus.
  • Allow cables to be safely deployed through pull lines or strings using less than 50 lbs of force, and through cable blowing techniques at typical deployment speeds of 100-200 feet per minute.

Placement of cable

With microduct cabling, bundles of small microducts may be installed in larger protective duct (e.g., PVC conduit). Bundles of microducts can also be factory pre-installed. The microducts can be branched very easily in the network. At any place of choice, a window cut is made in the protective duct and the microduct of choice is cut. This microduct is then connected, using a simple push/pull connector, to a microduct that branch to the desired location.

As indicated in GR-3155, cable is typically placed into the duct in one of three ways:

  • It may be pre-installed by the duct manufacturer during the extrusion process.
  • It may be pulled into the duct using a mechanically assisted or hand-drawn pull line.
  • It may be blown into the duct using a high air volume cable blowing apparatus.
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Why Cable blowing?

Traditional cable pulling methods are very sensitive to the condition of the duct and to the number of bends and undulations throughout the duct route. Therefore, for microducts, air-blown cable installation techniques are expected to be the most useful. Air-blown cable installation requires the use of a device that injects a high volume of air into the duct, at pressures as high as 20-25 psi. The viscous drag forces generated by the rushing air along the length of the cable act to reduce or overcome the friction between the cable and the duct.