Q: We had a contractor run one four-strand fiber backbone to every classroom in an elementary school. Two strands are "dark" for now, and the other two are connected to a "dumb" hub in the classroom, with the main hub located in the "headend" room. In some areas, when making this fiber connection, the contractor stripped back the cable sheath in excess of two feet. This appears to leave the fiber strand dangerously exposed to possible damage. Are there any industry standards that limit stripping back the sheath to only few inches, or that recommend other means of protecting these exposed strands?
Scott Rose
JGA Architects
Portland, OR
A: I think Scott`s description of two feet of unjacketed buffered fiber in an elementary school classroom as being "dangerously exposed to possible damage" is an understatement. This fiber will prove to be no match for inquisitive children.
I called Scott to make sure I understood exactly what had been installed, and it was not as bad as I had envisioned. An optical-fiber distribution panel is installed in the headend room, with optical-fiber patch cords connecting the front of the optical-fiber distribution panel to the hub ports. The classroom cable setup is another story, for example:
The cable exits the electrical box in the wall.
The cable sheath has been removed from the fiber cable.
Two of the four fiber strands are terminated on ST connectors, plugged directly into a port on the dumb hub.
The two unterminated strands are simply lying behind the dumb hub.
My initial reaction was that the adapters (couplers) and work-area cables (optical-fiber patch cords), which are specified in the ANSI/TIA/EIA-568A standard, are missing in the classrooms. Closer examination of TIA/EIA-568A, however, shows nothing in the current standard that precludes such an installation for active fibers.
Before the letters, faxes, phone calls and e-mail begin to fly, let me explainº
The first part of the question is easy to answer: Why is there so much unjacketed fiber at the end of the cable? Section 12.4.5 of 568A says, "A minimum of 1 meter (3.28 feet) of two-fiber optical-fiber cable or two buffered fibers shall be accessible for termination purposes."
The answer to the second part of the question is more complex, however. Section 12.4.5 states that the telecommunications outlet/connector box "shall be securely mounted; shall be capable of terminating two fibers into a 568SC adapter; and shall have the ability to secure the optical fiber cable and provide for a minimum of 30 mm (1.18 inches) of bend radius."
For the active fibers, there is no requirement to install a telecommunications outlet/connector box, adapter or work-area cable. That is a design decision.
Section 12.4.5 also says that "optical-fiber runs intended for future connections shall be housed in a telecommunications outlet/connector box."
The standard does not require a telecommunications outlet/connector box for the active strands, but one is required to house the "dark" fibers.