The impact of water on fibre optic cable

Fiber optic cables are resilient, but still need protection from damp and humidity, writes Asem Shahid of Datwyler

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The impact of water on fibre optic cable Asem Shadid managing director, Datwyler Middle East.
By Staff Writer Published  August 24, 2016

Years ago, in order to protect cables from water “creep” caused by capillary action, or at least keep it to the bare minimum, the stranding gaps in stranded cable assemblies were packed with petroleum jelly, a Vaseline-like gel. This solution has two drawbacks, however: the filling is highly flammable and the installer has to remove this gel from the bundles again, a very time-consuming process requiring special detergents which then have to be disposed of as hazardous waste.

Innovative cable manufacturers like Datwyler have therefore developed a different method of meeting the requirement for longitudinal watertightness. Nowadays manufacturers fill the stranding gaps and strain relief elements – glass or aramid yarn – with swellable materials. If the cable is damaged, these materials absorb any water which has penetrated and seal the site of the damage. Unlike a petroleum jelly filling, swellable materials do not contribute to fire propagation. Last but not least, there is no need to clean the bundles when processing the cables.

Datwyler tests the longitudinal watertightness of its FO Out-door and FO Universal cables to standard IEC 60794-1-2-F5 using Method B, which simulates more stringent conditions. Whereas Method A describes the penetration of water into a damaged cable, Method B examines the behaviour of the cable when water is able to penetrate into an open end not sealed by a shrink end cap. The key test criterion specified by Datwyler is that the spread of water in the cable should not exceed three metres within 24 hours.

Tested for ease of outdoor installation

Following on from the question of whether universal cables are suitable for burying and installing in cable duct systems, it should be noted that of course all Datwyler FO-U cables have passed the suitability test for outdoor installation. This test simulates accelerated weathering and reproduces damage which can be caused by sunlight, rain and dew. During testing the materials are exposed to alternating cycles of UV light and moisture at controlled high temperatures. The action of sunlight is simulated by special UV fluorescent lamps, the impact of dew and rain by condensing moisture and/or water spray. Within a few days or weeks the test thus reproduces damage which would take months or years to develop in the open air.


Datwyler’s Fibre Optic Universal (FO-U) cables are suitable for indoor and outdoor installation. For safety reasons, however, Datwyler recommends that universal cables should not be buried directly in the ground or routed in ducts or pipelines – except for dry cable duct systems. It is preferable to use Datwyler’s longitudinally watertight and “virtually laterally watertight” FO Outdoor cables (FO-O) in cable duct systems at risk of water penetration or in which there is permanent standing water.

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