Many structured cabling installations begin with the preparation of a detailed written specification for each system component. Such specifications may be necessary to ensure the correct product is used for the intended application. Specifications also ensure all products offered are equal in a competitive-bidding situation. Consultants and end users often find that they lack the breadth of knowledge or experience necessary to prepare a complete, detailed specification for optical fiber and fiber optic cable. This fact is not surprising because it takes a significant effort to keep abreast of changing product offerings as well as the most recent product evaluation and measurement technology. However, consultants and end users can use industry standards to specify the necessary products without having to delve into excruciating detail.
Specifications for optical fiber and cable can be, and often are, long and arduous; they address a myriad of technical considerations. These considerations include mechanical, environmental, and dimensional characteristics, not to mention the finished product’s compatibility with building codes and transmission equipment. Consultants and end users frequently prepare lengthy specifications, attempting to cover all pertinent details. This effort requires a thorough knowledge of cable design, optical science, and the details of scores of measurement methods. Panels of industry experts have developed national and international standards for fiber and cable; these standards can be the basis for the desired brief, accurate, detailed specifications.
Cables intended for direct burial underground should, in most cases, incorporate a steel tape armor for protection against gnawing rodents. Metallic armor has proven to be an effective rodent
protection in controlled tests.
For aerial installations, outdoor fiber optic cable require a messenger wire for lashing. However, some cables have an integrated messenger wire in a figure-eight cross section. Also available today are some all dielectric self-supporting aerial cables, which contain no metallic elements but have sufficient tensile strength to support their own weight and a reasonable ice and wind load.
The most popular loose tube cable includes buffer tubes, each of which contains one to 12 color-coded fibers. Some other cables include ribbons of fiber, rather than loose fibers in buffer tubes. Up to 24 fibers, joined together side-by-side, form a fiber ribbon. Stacks of these ribbons are in buffer tubes, creating a cable with a large number of fibers in a small cross-sectional area. Ribbon cables are popular in telephony and other long-haul applications and useful in crowded ducts where dense packing offers an advantage. Mass-fusion-splicing technology allows installers to splice 12 fibers in a ribbon simultaneously, offering labor savings in high-fiber-count applications. Ribbon cables are not common in premises applications but may become more popular as fiber becomes more prevalent in premises networks.
Indoor outdoor cable incorporate the characteristics necessary for both applications; they are waterblocked for moisture protection and are sunlight-resistant. Indoor/outdoor cables also meet one or more of the code requirements for flame-spread resistance and smoke generation.
They can be useful in eliminating a splice point for a building-to-building run in a campus environment. They resemble outdoor cables more closely than indoor cables in design and appearance
and usually require a fanout kit for field termination.
A detailed cable specification considers all environmental and regulatory factors that concern the installation environment, including temperature, mechanical loading, moisture, sunlight,
flammability, rodents, and chemicals. Fully specifying each cable also requires a test or measurement method and criteria. Once again, standards are available to simplify this task.
Two sister documents published by the Insulated Cable Engineers Association (ICEA-South Yarmouth, MA) are useful as detailed product specifications. The ANSI/ICEA S-87-640 Standard for Outside Plant Communications Cable and the ANSI/ICEA S-83-596 Standard for Fiber Optic Premises Distribution Cable cover outside- and inside-plant cables, respectively. A third document, which will be designated S-83-696 and is currently in the works, will address indoor/outdoor cables. In addition to detailed references for test method, loading, and failure criteria for finished cable, these documents also include similar details for the optical fiber. ANSI/ICEA S-83-596 includes a summary of the flammability listing requirements from the NEC. Referencing these documents as appropriate for indoor or outdoor cable ensures you have included a full battery of environmental and mechanical testing and failure criteria in your specification.
In the United States, the federal government is another source for a detailed product specification. The Department of Agriculture’s Rural Utilities Service (RUS) has published a document entitled Specification for Filled Fiber Optic Cables, which provides detailed product specifications for singlemode and multimode fiber, as well as OSP loose-tube cable. The RUS specification even outlines requirements for production and type testing as well as data reporting and manufacturers’ recordkeeping. The RUS conducts technical reviews of cable manufacturers’ products and programs and includes compliant companies’ products on an “accepted list.” By specifying that an OSP cable must be RUS-listed, an end user can take advantage of the RUS’s efforts.