Allied Encyclopedia: Water-blocked Cable

What is water-blocked cable?

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. Water-blocked cable can save both hassle and repair costs.

How does water-blocking work?

Before you get to the special water-blocking components, the first line of defense is 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 and wet water-blocking.

Dry water-blocking 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 is the process of adding a water-blocking gel to the shield and allowing it to fill in the nooks and crannies 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 method used depends on the application—it determines the materials used too. 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 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.

Telecommunication cables in a storm

Telecommunications cables need to be able to withstand weather-related water damage.

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.

Finding water-blocked cables

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.”

About awcwire
Allied Wire & Cable is a value-added manufacturer and distributor of electrical wire and cable, tubing, and more. We are a family owned and operated company, serving a wide range of industries, including the military, automotive, aerospace, and telecommunications markets. Allied is headquartered in Collegeville, PA. Additional locations can be found across the US, in Merrimack, NH, Tampa, FL, Pewaukee, WI, and Las Vegas, NV. For more information on Allied, visit our main website at

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