Flexibility is a measure of how much movement a cable can tolerate at a given time. Flexibility comes in many types; torsional, rolling, bending, and variable all describe different kinds of flexibility.
When a cable is bent, twisted, or pulled into positions other than its original state, its flexibility is tested. Flexible cable can bend significantly and stay bent for a large amount of time without being damaged.
Will your cable need to be bent or curved around infrastructure? If so, you may need high flex cable, or cable with strong flexibility.
Often times when someone is looking for a very flexible cable, they want it to be very soft. They want it to be easy to manipulate or bend back and forth without the cable kinking or back twisting.
Flex life deals less with how the cable moves, and more with how often it can move in these ways without taking serious damage. Many cables can bend to some degree for limited use (e.g., installation). High flex life cable can bend repeatedly and regularly without disrupting the cable’s intended use, such as power supply or data transfer.
Will your cable be subject to repeated movement such as is needed in robotics? If so, you may need cable with a high flex life.
Ultimately, the distinction comes down to use and application. If your cable needs to move well, it must be flexible. If your cable needs to move often, it must have a high flex life. In many applications, such as industrial machinery or factory automation, both flexibility and high flex life are required.
Whether we are talking about flexibility or flex life, there are different types of movement to consider. Different materials may be chosen depending on how your end application and the cable will move.
Retractable. A coiled or spiral cable is intended to “snap back” into shape after being pulled or extended.
Torsional. When a cable is twisted, pulled, or rolled around its axis, it experiences torsional flex.
C track, Drag chain, or Rolling. Often seen in track systems, rolling a cable not only stresses the cable’s interior components, but also wears down the outer jacket over time.
Variable. More “free form,” variable flex may make a cable move on multiple points in multiple directions – often seen in robotics.
Bending. This “tic toc” motion often happens when part of the cable is stationary, and the other part is bent back and forth over a fixed object.
Continuous. In many industrial applications, flex isn’t occasional – the cable may be part of equipment that requires constant, repeated movement for the lifespan of the system.
Repetitive flexing can cause serious damage to wire and cable systems. Internal conductors may break, outer jackets can erode or tear, and friction can cause overheating. Not only does this decrease the lifespan of the cable, it can cause system downtime or damage. Luckily, there are various ways to achieve flex characteristics to avoid downtime or damage. Material choices in a variety of components including stranding, conductor insulation, braid, strength members, jacketing material and so on all have materials that can help increase flexibility or extend flex life.
When choosing stranding for a cable requiring high flexibility, a high strand count is best. The typical rule of thumb is “the more strands, the more flexible and the longer the lifespan”. From a movement and motion standpoint, a rope lay construction is by far the most flexible configuration – it is also by far the most expensive, highlighting the trade-offs buyers and engineers must constantly consider when choosing materials. Concentric stranding is a better choice when aiming to achieve a high flex life.