New water-blocking approach saves installation time

By STEPHEN HARDY

Although the threat from water damage may not appear to be as great for terrestrial fiber cables as it is for undersea strands, water and fiber do not mix wherever they might come in contact. Thus, most terrestrial cables feature some form of moisture protection. A new protection method now employed by several cable manufacturers promises to keep out water while reducing the cost and installation hurdles associated with the most common moisture-shielding methods.

Terrestrial cables, whether above ground or below, become susceptible to water damage if their jackets are breached by wear or mishap. Traditionally, water shielding has taken the form of tapes, greases, gels, or some combination of these methods applied to the cable just underneath the jacket. However, all of these methods add cost, weight, and volume to the cable and can increase installation time. Greases and gels in particular, which must be cleaned away from the fiber end when installing or repairing links, can lengthen the field technician`s day.

Owens Corning, Granville, OH, has developed a technique by which the super-absorbent polymers used in waterproof tapes can be applied to the strength members normally found in cable. By combining moisture protection with tensile strength provision in the same component--a glass fiber tensile yarn--cable construction is simplified, and installation time is decreased. Although the company is not the only vendor to offer a combined-component solution to moisture protection, the new technology, called AquaBlok, offers more polymer powder per unit length than other approaches, according to Tom Hager, senior scientist at Owens Corning.

Hager explains that when water enters a breach in the cable jacket and comes in contact with the treated strength member, the polymer will swell, thus stopping the leak. If the cable dries completely, the polymer will return to its normal state. The polymer will swell and contract to offer protection over the life of the cable, says Hager. With the new dual-purpose component approach, installers can save 40% to 70% of the time required to perform mid-span access or end splices of cable with grease or gel, he adds.

The water-swellable polymer can be applied without affecting the strength member`s performance, says Hager. He and Anne Bringuier of Siecor Corp., Hickory, NC, presented a paper at the most recent International Wire and Cable Symposium describing the use of the AquaBlok technique in an optical-fiber cable. In the example cable, the polymer-impregnated tensile yarn was incorporated in a pair of indoor/outdoor cables (see figure). The cables--a polyvinyl chloride cable and a low-smoke polyolefin type--exhibited environmental, mechanical, and water penetration properties that met industry requirements. The tensile performance of the yarn also met performance requirements, both in new and aged states.

Siecor represents Owens Corning`s first customer for the new water-blocking tensile yarn. The company has already introduced cable products incorporating the AquaBlok yarn. Opticable of France and Pirelli of the United States have also purchased such tensile yarn for incorporation into their products.

If the dual-compound approach works so well with terrestrial cables, will it eventually replace some of the protective tubing and other robust protection measures now employed with undersea cables? "I`d like to say yes," answers Hager. "Right now, [however,] the limitations with these super-absorbent polymers that are based on polyacrylates are that they don`t do really well in high-saline conditions; they don`t want to swell in very-high saline conditions." Hager says that there are new polymers that address these limitations that Owens Corning hopes to commercialize in the near future. However, no such technology is commercially available right now. q