When Push Comes to Shove, Select the Right Strength Members for Your Cable Application

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Cable Legend

July 29th, 2016 - Northwire’s well received and recently launched Extreme Materials – Robust Performance from Cable to Connector white paper merges decades of Northwire cable engineering expertise and LEMO connector leadership through the sharing of SME knowledge to design and manufacture custom interconnectivity cable and wire design solutions.

Detailing cable construction from the inside out, the role and importance of strength members within the design of the cable assembly is featured in the white paper.

Fortifying a cable design with push strength, pull strength, mechanical strength, and rigidity, strength members provide both a functional and protective role in the world of connectivity. Together, Northwire and LEMO’s cable and connector design engineers gather a full understanding of the cable assembly’s end application and environmental considerations as with underwater cable, medical cable, and rugged cable used for industrial and aerospace/defense to determine the cable material and assembly design requirements.

Within the Extreme Materials white paper, Northwire SMEs summarize the three most common types of cable strength members:

  1. Fiberglass Rods

  2. Steel Strength Members

  3. Aramid Fiber

Northwire’s Director of R&D, Kevin DePratter, provides insight for the utilization of fiberglass rods and notes, “We use fiberglass rods when a cable has to be extremely rigid because the cable is being pushed through the pipe. One extreme application is for sewer system inspections where there is a camera and connector on the cable. The rod enables the cable to stand straight out. This gives the cable great compressive properties and a lot of push/pull strength.”

The advantages of steel strength members are explained within the NWI-LEMO white paper, noting its use in cable and wire applications where pulling strength and compressive strength are needed. Steel strength members (or steel cords) are incorporated within LEMO and Northwire’s SMPTE HD AV offerings. Varying requirements for weight and durability dictate the type of steel strength member utilized within the cable design. The characteristics of stainless steel strength members include exceptional strength at only 3/16th of an inch while galvanized steel provides pull strength of approximately 500 Newtons without breaking as well as superior compressive strength.

An extreme material, aramid fiber (or DuPont’s brand, Kevlar®), regularly used for protective apparel, excels in providing extreme pulling strength in cable and can be stranded in various configurations to deliver different levels of strength. A bundle of four strands provides 450-600 Newtons of pull strength. While it is not rigid, it does offer high compressive strength without adding significant weight. If aramid fiber is used in a cable system, special attention must be given to the cable’s termination, as incorrect termination can lead to weak points in the fiber.

When determining a strength member for a cable design, NWI SMEs advise asking:

  1. What type(s) of strength are required?

  2. Does this cable need to be rigid or flexible?

  3. What is the plan for termination and connectorization?

Learn what questions you should ask when selecting a cable and connector assembly for your application by downloading the Extreme Materials white paper, or connecting with a NWI cable engineering expert at