Which cables are resistant to sea water?
In principle, most materials used in the cable industry are resistant to salt or sea water. Even though some plastics absorb more or less water than others, it is largely irrelevant whether the cables are made of PVC, PUR, chloroprene rubber, PTFE or even silicone. However, caution is advised in the case of some halogen-free and highly flame-retardant cables made of special, highly filled polymers. The flame-retarding additives can be strongly hygroscopic and are thus easily saturated with water.
Even if the cable sheath compound displays no negative effects when exposed to sea water, not every cable is suitable for maritime use. At high sea in particular, cables are subjected to high levels of UV radiation and must be sheathed accordingly.
Another factor to be considered is whether the cable only makes occasional contact with sea water or is used underwater on a permanent basis. As the water depth increases, so does the pressure on the cable. This is referred to as the water column. The pressure for a 1 metre water column is 0.10 bar. Therefore, at a depth of 100 metres, the pressure is already 11 bar (100 m x 0.1 bar = 10 bar + 1 bar air pressure at sea level). At this pressure, cables with many air cavities in the core stranding can become compressed, or the water may gradually diffuse through the cable jacket and insulation and reach the conductor.
In many cases, cables intended for such applications are chosen indiscriminately due to a distinct lack of alternatives which have been thoroughly tested and approved for underwater use – ÖLFLEX® AQUA RN8 being one example. At relatively low water depths, this is generally without problems. However, deep-sea applications definitely necessitate special cables, which are designed to cope with the conditions and water pressures prevalent at such depths.