Fiber Optic Cabinets, Cables, Pedestals and Terminals

By Johnny Hill

One of the continuing ironies of Fiber-To-The-Home (FTTH) interconnect cable products is that while a great deal of effort has been expended to develop optical components that perform well under harsh conditions, many of the materials and specifications essential to these products—despite the environmental, routing and physical handling demands found in FTTH enclosures—are better suited to indoor applications.

Outside Plant (OSP) equipment such as fiber distribution cabinets, pedestals and optical network terminals are subjected to a huge array of environmental challenges.  These enclosures face attacks from lightning, pollution, rain and high winds; depending on the region they may also need to withstand floods, hurricanes, blizzards, earthquakes, forest fires and salt air.  Rodent, wild animal and insect infestations are a concern as well.

Of course, rack-mounted splitters, jumpers and other enclosure components are subject to extreme intra-enclosure conditions caused by these environmental factors.  Summertime temperatures inside a distribution cabinet can reach +180° F in some parts of the U.S., greatly affecting cable material, while humidity, condensation, corrosion, sand and dust can wreak havoc on connectors and hardware.

In response to these challenges, Telcordia Technologies, the USDA Rural Development Telecommunications Program, NEMA, and other standards organizations have instituted performance standards for Passive Optical Network (PON) interconnect cables.  For example, Telcordia has a generic requirement defined for jumper cables used with pre-terminated multi-fiber assemblies in OSP environments; this requirement, GR-326, addresses signal performance across a protected route path with proper bend radius.

The trouble is that the real world does not always match such controlled specifications, especially under the temperature extremes found in OSP fiber distribution enclosures.  Traditional riser-rated materials that are also rated for outdoor use react very differently at -20° F than they do at +70° F.  The jacket becomes very stiff and memory-retentive, making it difficult to route a circuit because of its static state.

In addition, what happens if a jumper needs to be relocated or re-mated in the midst of an extreme cold snap?  If the prescribed route path proves difficult due to the stiffness of the cable, the technician may take a shortcut to the desired adapter.  This situation becomes a problem when temperatures begin to warm up and the cable “relaxes,” since the cable is not using the recommended route paths that are bend radius protected.

Inside-rated cable is designed to withstand temperatures of -4° F to +149° F, but it cannot meet an OSP ratings standard of -40° F to +185° F.  Extreme high and low temperatures, as well as repeated thermal cycling, can possibly cause intermittent power loss.  This scenario is often difficult to troubleshoot and causes a lot of frustration.