How to Specify Water-Resistant Fiber Optic Cable
Installing fiber optic networks in harsh environments, such as on the factory floor, requires special considerations. Here, Berk-Tek explains how to specify water-resistant fiber optic cable for demanding applications.
Fiber optic cables have become an integral part of applications such as data centers, local area networks, telecom networks, industrial Ethernet, and wireless. Each application requires a specific cable design based on performance requirements, environmental conditions, and installation type.
Water-resistant fiber optic cables are designed and specified for installations where the cable will come in contact with water or moisture. Examples include aerial, direct buried, or in conduit. The cables in these applications are exposed to or can be temporarily submerged in water, so they contain either a water-resistant gel-filled or gel-free (dry gel) polymer.
There are three different types of cable, which are specified based on the environment and location where they are installed: Outside plant cable (OSP), indoor/outdoor, and indoor. With the exception of indoor cables, all cables contain water-resistant gel-filled or gel-free material to protect them from water and moisture. Before the use of gel-filled and gel-free materials, flooded core was another water-blocking method that is rarely used today (it has been replaced with gel-filled).
The gel is a gooey substance that must be removed when accessing and installing the cable. Gel-free cables, which are now more widely used, contain a super-absorbent polymer powder that is activated when it comes in contact with water or moisture. This blocks the water from penetrating the cable and allows for some expansion and contraction with temperature changes. Indoor cables do not contain water-resistant material since they are not typically exposed to water. Indoor (and indoor/outdoor) cables must meet additional flammability requirements dictated by local codes, such as the National Electrical Code (NEC).
Water-Resistant Cable Designs
Water-resistant materials and cables are included in many industry specifications and standards. Two different specifications that cover cable water resistance are TIA-455-82 (FOTP-82-B), the fluid penetration test for fluid-blocked fiber optic cable, and IEC 60794-1-22 section 7, method F5. The standards from TIA and ICEA refer to FOTP-82-B as a test for water resistance, but there are no specific water-resistance requirements mentioned in the NEC.
Generally, there are two basic water-resistant cable designs:
- Loose tube cables (used for OSP and indoor/outdoor)
- Tight-buffer cables (primarily used inside buildings)
In loose tube cables, the tubes surrounding the fibers can be filled with water-absorbent powder or gel that withstands high-moisture conditions, making them excellent for outside plant applications.
Even though most tight-buffered cable designs are specified for indoor use, some of them are designed with water-resistant powder and yarn, making them suitable for some indoor/outdoor applications.
When specifying water-resistant cables, one must consider the application, the installation location, and the appropriate cable design and type according to specifications and standards.
Author Raed Samamra is the fiber optic product business manager at Berk-Tek.