Custom Cable Assembly Series: Strength Members

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August 1st, 2017 - What they are: A strength member is the component of a cable with the function of adding support to preserve the cable integrity. Strength members add both function and protection to connectivity solutions. There are several options including steel, aramid fiber, or a stiff fiberglass rod that runs the length of the center of the cable. The strength member helps the cable withstand different types of movement including:


  • Pulling
  • Torsion
  • Continuous
  • Variable
  • Bending
  • Rolling

Why you need a strength member: Cable that is expected to perform in tough or rugged environments can benefit from the reinforcement that strength members offer. The strength member core makes sure that there isn’t pull on the connector. They offer support, strength, and add longevity to the cable.

How to choose: When deciding what material and type of strength member ask yourself three questions:


  1. What is the pull strength requirement?
  2. Does this cable need to be flexible?
  3. Does the strength member need to be terminated to the connector?


Aramid fiber, such as Kevlar® is a strong material ideal for extreme pulling strength. Aramid fiber can be stranded in a variety of configurations to achieve differing 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.

Steel strength members are used in applications where pulling strength and compressive strength are critical. There are different types of steel strength members that may be used depending on weight requirements and durability. Stainless steel strength members provide excellent strength at just 3/16th of an inch. Galvanized steel provides pull strength of about 500 Newtons without breaking, along with superior compressive strength.

Fiberglass rods are extremely rigid and good matches for pulling or pushing applications. The fiberglass has great compressive properties and is very strong. It is important to consider the environment since fiberglass cannot handle extreme heat or cold. It cracks below -20C and above 80C.

A custom cable designed for a demanding end application without a strength member is like the Wild West without cowboy hats, it just isn’t right.