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Thursday, April 17, 2003
Why municipal utilities usually use ADSS cable for their aerial fiber runs
Why municipal utilities usually use ADSS cable for their aerial fiber runs ADSS (all-dielectric self-supporting) fiber optic cable is used primarily near energized electric conductors by power utilities. The cable is more robust (due to more Kevlar fibers for strength) and can support itself without having to be lashed to steel messenger wires. (Lashing fiber cable to messenger wires is the standard method used by telcos and cable TV companies to install fiber cable aerially).
Being able to install ADSS in the "supply region" (the area near the conductors) instead of the "communications region" is one way electric utilities can install fiber cable at lower costs than telcos and cable TV companies. Safety codes allow ADSS to be installed virtually anywhere in the area near the conductors since it's non-conductive and does not require a metallic messenger. (It's almost impossible to safely install a messenger wire in this area then lash a duct cable to it without electrocuting someone.)
That means there's almost always space for ADSS somewhere on the pole. In contrast, it's frequently impossible to find room for another cable and messenger when lashing fiber cable in the communications space; when this happens, the company installing the new fiber cable has to pay the entire cost of replacing the pole while it's energized at 12kV or higher -- an expensive proposition ($3,000 or more in skilled labor).
When Fiber Planners designed the 110 mile ADSS system for Bristol Virginia Utilities Board's FTTH backbone, only 1 pole had to be replaced. Municipal utilities using lashed fiber cable on aerial runs typically replace 5% to 40% of their poles, depending on how crowded they are.
Our cost studies have shown municipal electric utilities using ADSS in FTTH (fiber to the home) save 10% to 20% in total outside plant costs by avoiding these pole replacements. That's after factoring in the slightly higher cost of this type of cable and the more highly skilled crews that are needed to install it. It also includes the cost of ADSS design specialists; the cable installation has to be planned out pole by pole ahead of time.