Example of Specification for Buffer Tubes in Loosetube Cables

Buffer tubes or loose tubes in loose tube cables shall be able to meet deployment conditions applied in the installation field. Each buffer tube shall contain certain number of optical fibers. The number of optical fibers in a buffer tube may vary from 1 to 12 depending on the cable fiber count. Typically 4, 6 or 12 fibers are placed as appropriate for the respective size cable. For higher fiber count cables, buffer tubes may contain 16 or 24 fibers per tube.

All optical fibers in a buffer tube shall be individually identified by coloring throughout the length. For buffer tubes having more than 12 number of fibers, identification can be done by using ring marked color fibers. Optical fibers shall be placed inside a loose buffer tube. The nominal outer diameter of the buffer tube shall be 3.0 mm. Supplier is free to offer alternative size for buffer tube, but shall provide data to support the design suitability.

Each buffer tube shall be color coded with distinct and recognizable colors in accordance with the most recent version of EIA/TIA-598, Optical Fiber Cable Color or IEC 304. Alternatively Munsell color chart can also be used. In buffer tubes containing multiple fibers, the coloring shall be stable during temperature cycling as stated under “Fiber Specification Parameters” and shall not be subjected to fading or smearing onto each other or into the buffer tube gel filling material. Coloring shall not cause fibers to stick together.

Buffer tubes shall be of a dual-layer construction with the inner layer made of polycarbonate and the outer layer made of polyester. In case of double layer, the inner layers could be nylon and outer layer could be polycarbonate or polybutylene teraphthalate. Alternatively buffer tubes shall also be made of single layer using polybutylene teraphthalate, in whic case the supplier shall submit enough supporting data to show the performance of the tube.

Each buffer tube shall be filled with a non-hygroscopic, non-nutritive to fungus, electrically non-conductive, homogenous gel. The gel shall be free from dirt and foreign matter. The gel shall be readily removable with conventional nontoxic solvents.

Buffer tubes shall be suitable to strand around a central member of the cable using a reverse oscillation stranding process. buffer tubes shall be mechanically strong to wrap around central strength member. The central strength member material may differ from non-metallic to metallic depending on the cable design.

The buffer tubes shall be resistant to external forces and shall meet the buffer tube cold bend and shrink requirements of relevant international standards. Supplier shall provide sufficient data to prove performance of the buffer tubes simulating equivalent installation conditions in harsh environmental conditions.

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Author: Nimura

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