What is Water-Blocked Cable?
The water-blocked cable is any type of cable specially designed to defend against water damage, offering protection beyond the water-resistant properties of cable jackets.
While most jacket materials are sufficiently water-resistant for standard use, some applications are more demanding. Even if water damage doesn't fully disable the cable right away, it can negatively impact performance and signal strength. The water-blocked cable can save both hassle and repair costs.
How Does Water-Blocking Work?
Underneath the special water-blocking components lies the first line of defense: a jacket with excellent water-resistance, such as high-density polyethylene (HDPE.) Choosing a jacket is sometimes easier said than done, however, as you may have to weigh mechanical against electrical properties and make compromises. For example, highly moisture-resistant HDPE might be too stiff to meet your needs, but perhaps LDPE (low-density polyethylene) is flexible enough. It’s not quite as moisture-resistant, but still effective.
There are two main methods of water-blocking:
- Dry water-blocking— this involves wrapping the inner cable components with an absorbent layer of impregnated fiber, be it yarn or tape. If water gets through the cable sheath to that layer, the fiber will swell up, preventing further propagation. This minimizes the damage and extends the life of the cable. The water-swellable yarn or tape doesn’t impact the dielectric characteristics of the cable and can be easily cut when it’s time to add connectors.
- Wet water-blocking— this is the process of adding a water-blocking gel to the shield and allowing it to fill in any open space in the cable. This is also highly effective in preventing water from traveling down the length of the cable. The gel, however, is not conductive and must be removed after stripping the cable in order to add connectors.
The best method of use, and the materials, depends on the application. There are multiple types of yarns and tapes as well as a number of gel compounds with different viscosities, hardnesses, and temperature ratings for different applications. Some are designed for copper core cables, while others are best suited to a loose tube, slotted core, or ribbon constructions.
Water-blocked connectors are also available for outdoor terminations, but if the cable will be terminated indoors, make sure NEC guidelines for running outdoor cables indoors are being met.
What Applications Benefit From Water-Blocking?
Naturally, water-blocking is prevalent in underwater cabling. It is also a common attribute in mil-spec marine wire standards, though not all shipboard cables need to be water-blocked. A lightweight, low-smoke power cable, M24640/1 DX Cable is not watertight, but it is suitable for use in control rooms and locations aboard the vessel which are not likely to endure harsh exposure to the elements. If the cable will be required to run exposed across the deck, the DXWB variation of the DX cable is water-blocked and a more suitable choice for the application.
Watertight cables are also useful in offshore drilling and rugged industrial environments. Underground medium and high voltage cables in areas likely to get wet are often water-blocked, as are many telecommunications cables. Loose buffer fiber cables especially benefit from water-blocking, as their constructions could permit water to travel freely down the length of the cable.
It is important to note that if you are trying to find water-blocked cables online, it may help to vary your search terms. Some manufacturers and organizations use the term “water-blocked,” but others— like the US military and Allied— use the term “watertight.”