Dry blocking technology makes for neater, easier installation.
Thomas Debiec / Berk-Tek
Scrunched up faces. Icky-pick. That is the general reaction when outside plant fiber optic cables are the topic of discussion. Thanks to recent technology, however, a new generation of smaller, lighter, easier to install outside plant cable is emerging. It still maintains the best traits of its predecessor, but without the mess.
Optical fiber manufacturers such as Alcatel, Corning and Lucent have improved their processes in fiber transmission characteristics, as seen by the release of optical fibers with greatly enhanced bandwidth. They have also improved the manufacturing methods to reduce the size and frequency of flaws in the fibers. Additionally, the coatings have been greatly improved, enabling the fibers to better withstand mechanical punishment and maintain their optical transmission characteristics. All fibers manufactured by these companies have break strengths in excess of 100 kbits/square inch.
The outer acrylate coatings have been improved to the point that the fibers themselves are able to withstand immersion in water for extended periods of time with no change in their properties. And since the fibers are now better able to withstand moisture around them, protecting the fibers in buffer tubes no longer requires hard-to-handle gel.
Super polymers vs. gel
In the last several years, dry, super absorbent polymers (SAP) have provided cable manufacturers opportunities to enhance their products. The ability of these polymers to swell to 800 times their original size has allowed for the development of a more user-friendly cable that still meets the rigorous requirements of the outside plant environment. SAPs have been used to coat optical fibers used in the cable core, but until recently they had not been used inside the fiber tubes.
Even though the size of each SAP particle was minimal, cabling engineers regarded them as boulders, fearing that the particles would greatly affect fiber attenuation. But thanks to recent technological advances, the particles have been reduced in size so that it is practical to use SAPs within outside plant cables, eliminating the need for gel, and all the while maintaining the long-term viability of fibers in the buffer tubes.
No more messy gel inside the cable offers a further design advantage when combined with the right materials: the ability to meet flame ratings required for installations in air-handling plenum and riser applications. This advantage increases the cable's versatility for both outdoor and indoor applications.
Icky-pick be gone
By comparison, traditional, gel-filled outside plant cables are affectionately known as "icky-pick" because the material is, well, "icky" to work with. Just ask an installer.
"I've cleaned a lot of gel-filled cables and it is messy," says Rich Tillman, RCDD/LAN specialist for Atlanticom Technologies, a cabling systems and network services provider in Trenton, NJ. "You have to remember to clean (the gel off), and you have to clean up the room when you are done because the stuff gets everywhere. It's horrible."
Historically, outside plant cables have been filled with water-blocking gel to protect the fibers as well as inside the buffer tubes and in the interstitial areas of the cable core. Gel was required in these areas because the first generation of optical fiber coatings was less rugged than the products available today. Early fibers were especially sensitive to water, heat, and ultraviolet rays. Even indoor light could cause disintegration of some of the materials used in the cables. Although the fibers were shipped to cable vendors free from large faults, it took just one microscopic flaw induced by the presence of water to stress or break the fiber.
Meeting water standards
Industry standards have been developed to ensure that cable installation maintains consistency across the map. Telcordia (formerly Bellcore) GR-20 is the industry standard that specifies requirements for the cables used in the U.S. telephony network. The GR-20 standard requires that all outside plant optical-fiber cables be water-blocked so as to meet the requirements of TIA/EIA FOTP-82 for water penetration. This test ensures that the cable's integrity is not compromised by water if the jacket is breached. The Telcordia standard delineates cable requirements for mechanical tests, such as crush and impact, which help protect the fiber from damage during installation. The test for water-blocking, outlined in TIA/EIA FOTP-82, requires that the cable must be connected to a 1-meter head of water for 24 hours with no leakage allowed.
The Telcordia specification has been used for years, and millions of feet of outside plant cable have been manufactured to meet its requirements. But Telcordia is no longer pursuing the development and maintenance of specifications, and Insulated Cable Engineers Association (ICEA) has taken over responsibility. The ICEA 696 standard for indoor/outdoor cables is still under development, but specifies that any premise distribution cable installed between buildings must be water-blocked.
Some gel-filled cables are marketed today as indoor/outdoor-capable, but they do not meet these future ICEA requirements. Tight-buffered cables have been installed between buildings that do not have water-blocking mechanisms other than the outside cable jacket.
Technology that pays
With the new generation of dry blocking cables, however, engineers have designed a versatile product at a minimum cost premium over traditional gel-filled cables. In fact, many of these designs are less costly than tight buffer designs when the number of fibers in the cable increases.
But cable price is just a small part of the picture. Consider a 900-foot cable run using 12-strand fiber. The cable contributes only 19% of the overall installed cost, while labor contributes 66% of the cost. Anything that reduces cable installation and termination time helps to drastically reduce overall cost.
Compared to conventional outside plant cable, the simplicity and strength of dry blocking cables lets installers see a 50% reduction in the time it takes to prepare a cable end. Because there are no gels, the time to remove the buffer tube, clean the fibers and install a fanout kit is significantly reduced per tube. With labor a major installation cost, it is easy to see the cost advantages when terminating cables that contain multiple buffer tubes.
One for all
The versatility of dry block cable means one cable design can work for all installation and fire-rating requirements. The National Electrical Code requires a transition from an unrated outside cable to an appropriately rated cable within 50 feet of the entrance point. A dry block, plenum-rated cable can eliminate this transition point because it can be pulled directly into a plenum space. By eliminating the transition point, cost models show a reduction to the total installation cost of 26% for a 12-fiber cable, and 36% for a 72-fiber cable.
Sean Sheehan, vice president of engineering for Link Tech Inc., a network design and engineering company in Wyomissing, PA, says, "The dry block is so much easier to work with and less time-consuming. It's a much better solution than dealing with the extra materials and the time it takes for the gel-filled cables. The advantage is that you don't have any prep time to put the fanout kits on, where with gel, it takes a long time to get the cables ready to use the fanout kits."
Concurring that installation of a dry block cable can be less expensive than gel-filled cable, Sheehan notes, "We're using the same time estimate to prep the (dry block) cable as we do a premise distribution cable."
Adds Atlanticom's Tillman, "A cable like this has saved us as much as 10% labor on the job...the time and labor savings can be as much as 10% on a cable pull."
Installers also like the fact that dry block cable eliminates the transition point from outside and into a building. Installers are receptive to this concept and the cost savings associated with it. "The best thing about it," says Tillman, "is the time it saves us and the cost-effectiveness of the fact that we don't need to convert (a dry core cable) entering a building."
The cables also meet installation requirements for air-handling plenums. When cable runs are required to go from building to building and terminate in plenum spaces, the transition point required by codes can be eliminated. And eliminating that transition point and all the associated labor and connecting hardware can significantly reduce installation costs.
"It doesn't require converting from a non-plenum outdoor cable to a plenum indoor cable, so you can just keep on running," Tillman adds. Eliminating the transition point between the buildings, he continues, "also saves termination hardware that we don't need-like a splice panel-at the transition point once we've entered the building."
Atlanticom is using dry block cable in several environments. "We're using it the most in inter-building connections," Tillman said. "That may mean outdoor or underground. It may mean aerial or some transition method, or in a tunnel between buildings." Atlanticom, he says, frequently uses the cables in backbone and campus environments.
A competitive advantage
The technology used in today's dry blocking cables is a major advancement in the design of outside plant cables that are used in premises applications. Offering a cable that is robust, versatile, and cost-effective overcomes previous objections regarding conventional outside plant designs. Such dry block cables on the market today are giving contractors a competitive advantage.
Just two years ago, optical fiber that was packaged in a rugged, compact, loose tube construction did not come without its restrictions. Icky-pick, splice points and the need for fire-regulated transition points from outside to plenum spaces were the norm.
For those who choose to use the newer dry tube outside plant cables, these difficulties are now tales from "back in the day." The solvents and rags will not be missed. But now what will you do with those basement splice closets?
Thomas Debiec, RCDD, is technical training manager at Berk-Tek (New Holland, PA) and the primary standards representative for IEEE 802, which includes 10 Gigabit Ethernet. He is also a standards representative for ANSI X3T11 (Fiber Channel) and X3T12 (FDDI). Debiec is Berk-Tek's alternate representative to TIA 42.1-the standards body that developed the "Telecommunications Cabling for Commercial Buildings" standard. He has been involved in industry standards for more than ten years and is a 1979 electrical engineering graduate from Penn State.
You can contact him via e-mail at: firstname.lastname@example.org.