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Highly flexible cables and wires for constantly flexing applications

A very simple cable is made up of a solid wire and a plastic outer jacket. This cable can bend and retains this bending – as long as you don’t bend it too often, as otherwise the wire breaks. Simple cables like these are used in house installations. Once permanently installed, the cable remains in place for decades untouched. Solid wires like these are not suitable for many other challenging applications where cables sometimes need to be extremely flexible and movable.

Find out what flexible and highly flexible cables are, how they differ, how they are constructed, what properties they have as well as when and where they are used.

What are flexible and highly flexible cables?

The absolute majority of all power, control and data cables from LAPP are flexible. However, the degree of flexibility, i.e. the mobility and bending measurement of a cable, is determined by the design and material properties. Some cables only allow occasional bending, while others can bend millions of times. Some cables are also specially optimized for axial movement stresses, known as torsions.

Discover the ballerinas under the cables!

Did you know?

permanent, buried cables are generally rather rigid and inflexible. Find out in our Cable Advisor why this is the case and how permanent, buried cables differ from other types of cables
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How can flexible and highly flexible cables be moved and where are they used?

If cables remain in the position in which they were installed, this is referred to as fixed installation and static use. These fixed installation cables, which are typically used for building installation, are only moved for maintenance, repair or renovation. As a result, such cables are exposed to virtually no movement and, above all, no permanent flexing stress.
In an industrial environment, it is much more common for cables to be moved constantly and everywhere: on moving machine parts or processing stations on production lines, in cable chains, robots, wind turbines and oil rigs, in vehicles and motors, on cranes and commercial vehicles – even in applications where vibrations occur.
Let's take a look at the typical flexing stresses that may be faced by cables developed for flexible use or constant flexing:

Flexible cable routing

Flexible use

The cables are exposed to the conditions of occasional, unforced movement.

Typical applications
Machine tools, hand-held electrical devices, portable electrical devices, frequent reeling and unreeling of cable reels, etc.

Bending (linear movement)

Constant flexing

The cables are permanently exposed to the stresses resulting from the bending movement.

Typical applications
In horizontal and vertical cable chains for automated applications – one of the most grueling locations for a cable.

Here, power, servo and data cables are located close together and move back and forth as a machine works. Sometimes faster than five meters per second (16.4 feet per second) with more than five times the acceleration of gravity (5x 9.81 m/s²) (5x 32.19 ft/s²). The cables are laid in the cable chain in such a way that they’re bent in just one direction.

Torsion (three-dimensional movement)

Constant flexing

The cables are permanently exposed to the stresses resulting from the torsional movement.

Typical applications
A gentle, slow torsion occurs in the loop between the nacelle and the tower of a wind turbine.

By contrast, many industrial robots are much more dynamic and faster. Here, the cables rotate around themselves with high torsion angles and are also exposed to high rotational speeds and intense bending. The cables are designed for 3D movements.

What exactly is torsion?

Torsion does not mean, for example, a bending of the cable, i.e. a kink or a twist, but rather a longitudinal rotation of the cable around itself at a certain angle of torsion. This torsion angle is specified in degrees per meter (feet) of cable length. A typical value is 360°/m (360°/3.28 ft). Such a cable can be twisted once per meter (foot) around its axis without causing any damage – and it can do so in both directions. This applies to cables without shielding; with shielding, the value is typically 180° or half a turn per meter (3.28 feet).


The flexing stress of a torsion can either only act axially on the cable (rarely the case) or it is a combination of simultaneous bending and torsion (much more commonly the case).
In constantly flexing applications, strong forces often act on the cables. They must be equipped for high acceleration, strong deceleration and rapid changes of direction.

How are highly flexible cables constructed?

Highly flexible (data) cables are generally designed either for linear loads, as they occur in cable chains, or for torsional loads, which are predominantly caused by industrial robots. There are only a few cables that can withstand both bending and torsion over their entire service life. You can identify these at LAPP via the product name ROBOT.

Which properties are crucial for drag chain cables?

Cables must meet a number of requirements to be considered suitable for cable chains:

Drag chain cables have fine or extra-fine wire conductors for maximum movement flexibility. Highly flexible data cables generally have a 7-wire or even 19-wire copper conductor. Highly flexible power and control cables can easily contain more than 80 individual wires. As a result, the conductor is extremely flexible, so that braid breaks do not occur prematurely if subjected to mechanical stress in the cable chain or torsion application.
Drag chain cables have high flexibility and a small bending radius. Depending on the type, these products can be flexed continuously to the smallest permissible bending radius without impairing their functionality. The bending radius is defined as a multiple of the cable diameter (e.g. 10 x outer diameter). Note: The minimum bending radius of the cables must correspond to the bending radius used for the cable chain system!
Drag chain cables for power supply are characterized by having the smallest possible outer diameter. The multi-conductor variants usually contain no more than 25 conductors to be stranded. We also recommend dividing the required number of conductors between several cables. Wherever particular space savings or very large conductor cross-sections are required, single-conductor cables usually have a clear advantage (single-conductor cables, identifiable by SC in the product name).
The individual conductors of drag chain cables are stranded with different lay lengths, depending on the flexibility to be achieved. Both the stranded wires and the conductors are generally twisted because this improves flexibility. If all wires and conductors were to run in parallel, the wires and conductors on the outside would be stretched and the wires and conductors on the inside compressed every time the cable was bent. This would make the cable very rigid, single conductors could break, entire conductor layers could shift and lead to premature failure due to what is known as corkscrew formation. The following principle applies: The shorter the lay length, i.e. the conductor stranding, the more flexible the cable.
Drag chain cables are characterized by their extremely low weight. Ultimately, the cable chain must not only support its own weight, but also that of the cables and media hoses placed in it over a length in meters (feet), accelerate and finally brake.
Drag chain cables are made from jacket and insulation materials that meet drag chain requirements and the prevailing ambient conditions. The application often determines the material in this way!

Which cable design dominates among robot and torsion cables?

Provided that the bending radii allow it, special robotic cables can be used in the same way as highly flexible drag chain cables in drag chain operation, where linear continuous bending movements with firmly defined parameters act on the cables. However, drag chain cables cannot be used in three-dimensional robot operation. This is due to the design and can be explained in a simplified way by taking a look at the basic structure of cable chains and robotic cables.

With drag chain cables, the following principle applies: the shorter the lay length, i.e. the conductor stranding, the more flexible the stranding assembly. The exact opposite is the case with robotic cables, as the longer the lay length, the more gently torsion can be absorbed. This is because if the lay length is too short, the conductors could break during the three-dimensional movements.

Robotic cables have sliding foils over the outer layer and, in some cases, also between the layers, so that the conductor assembly can move easily within the jacket when subjected to torsion.

In addition, the outer jacket is usually manufactured as a hose extrusion and not as a press extrusion to make it easier to rotate the conductor assembly.

Which application parameters must be observed?

The aforementioned properties have a major impact on the following application parameters and need to be considered when selecting a cable.

Note: The cable chain must always be designed in accordance with cable/hose features and not the other way round. However, the service life of drag chain cables largely depends on the correct installation in the cable chain, the type of chain and the quality of the chain.

What type of movement will the cable be subject to? Linear movements, rotations, combined movements?

Relevant for cable chains

To what extent can the cable be bent? The bending radius has a decisive impact on the service life: the smaller the bending radius, the greater the strain on the cable.

Relevant for cable chains

The travel distance indicates the number of meters (feet) over which a drag chain cable can be installed horizontally or vertically suspended in a cable chain.

Relevant for cable chains

To what speed is the drag chain cable exposed in the cable chain? Power and control cables as well as data cables are typically suitable for speeds of up to 10 m/s (32.81 ft/s).

To the travel speeds of LAPP drag chain cables

What acceleration is the cable exposed to?

Data cables are generally accelerated up to 10 m/s2 (32.81 ft/s²). Acceleration of up to 80 m/s2 (262.48 ft/s²) is possible for power and control cables.

To the acceleration values of LAPP drag chain cables

Relevant for cable chains

How many bending cycles does the drag chain cable withstand in the cable chain? This means how often it can be bent without any noticeable functional impairment. Our drag chain cables are tested for several million bending cycles. The actual number depends heavily on the chain parameters used and the prevailing local ambient conditions.

Relevant for torsion applications

How many torsion cycles can the torsion cable withstand in the application? That is, how many times can it be rotated in an axial direction around the specified angle without any noticeable functional impairment? Our torsion cables are tested for several million torsion cycles. The actual number depends heavily on the prevailing local ambient conditions.

  • What temperatures prevail in the application?
  • What moisture is the cable exposed to?
  • Will the cable be used indoors or outdoors?
  • Are oils or chemical substances present?
  • What is the prevailing degree of pollution?

How flexible are fiber optic cables actually?

Fiber optic cables are the first choice for very high data transmission rates over long distances. They consist of plastic optical fiber (POF) for shorter distances of up to 70 meters (229.67 feet), plastic cladded fibers (PCF) for distances of up to 100 meters (328.1 feet) and glass fibers for even larger distances and applications requiring the highest data transmission rates. In principle, all fiber types are suitable for flexible applications as long as the recommended bending radii are observed. Then you don’t need to be afraid that a glass fiber optic could split. However, in order to achieve the highest possible transmission performance, the bending radius in fiber optic cables should be at least 15 times greater than the diameter. While a lower bending radius will not cause them to break, it will lead to increased attenuation, meaning that light is lost in the tight curve and the signal quality will suffer. The material enveloping the fibers largely determines how well a fiber optic cable can withstand movements. Aramide fibers, i.e. synthetic fibers that give bulletproof vests or fiber-reinforced plastics their exceptional properties, are often used here. If the cable is stretched, the textile jacket absorbs the tensile force and prevents the fiber optic cable from also being stretched.

How are highly flexible data cables tested?

The decisive thing is not what is on paper, but what happens under real conditions. In the LAPP test center, the tests are therefore carried out in such a way that the results apply to many real applications and we do not have to make false promises.

Our center has state-of-the-art testing equipment that tests more than just the general service life of the data cable in the cable chain. In other words, after how many bending cycles does a conductor break? Rather, the transmission performance is examined across all cycles. This allows us to trace exactly after how many bending cycles, for example, a Cat.6A drag chain cable no longer meets the requirements of IEC 61156-6. If the transmission-critical parameters, such as the damping values, deteriorate after a certain number of bending cycles, this is no longer a satisfactory result for us. For ETHERLINE® data cables, a simple continuity check is simply not enough for us!
Our cables for wind turbines are tested for torsion in an old, twelve-meter-high (39.37-foot-high) elevator shaft. Other manufacturers merely test shorter cable lengths twisted at more acute angles and extrapolate this data to estimate the figures for longer cable lengths.

Our highly flexible cables – a small selection

With the highly flexible cables from LAPP, you can ensure the productivity of your machines and plants.

In moving applications, and specifically where the movement ultimately takes place, it's necessary for every smallest component to be movable. Under no circumstances may the stresses be permitted to cause damage. This is because a high level of plant efficiency can only be achieved when all components last a sufficient period before maintenance becomes necessary, i.e. when they are available and deliver the required performance.

Highly flexible power and control cables from our ÖLFLEX® product brand

Electricity? – The essential power without which a machine would not function at all.
Signals? – The decision makers that determine how a machine works.

Highly flexible Ethernet data cables from our ETHERLINE® product brand

Highly resilient, highly bendable or remarkably torsionable – these are our ETHERLINE® data cables with different transmission properties (performance according to cable category "CAT").  The specific cable design (2- or 4-pair, foils over the conductor assembly, with or without a cross separator, many with a Fast Connect design and inner jacket, jacket material PVC or PUR) has a significant influence on the future application area.

Highly flexible fieldbus data cables from our UNITRONIC® product brand

Fieldbus systems also require the dynamic use of cables. High resistance to electromagnetic interference goes without saying. To prevent errors in signal transmission, the correct cables should always be selected. The following table provides a brief overview of highly flexible data cables for the PROFIBUS and CAN fieldbus systems.

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Highly flexible fiber optic cable from our HITRONIC® product brand

If fiber optic cables are to withstand the highest bending stresses, products that are particularly elastic and mechanically resistant must be used. Plastic-jacketed fiber optic cables with a high-quality PUR outer jacket are available for this purpose. Large bending radii enable use in the cable chain without having to worry about optical losses in data transmission. Discover our top recommendations below:


For cable chain applications, torsionable to a limited extent

Halogen-free FRNC single jacket and halogen-free, flame-retardant outer jacket with resistance to oil, petrol, acids and alkalis, min. 3,000,000 bending cycles at 3 m/s (9.84 m/s) speed and 3 m/s2 (9.84 ft/s2 ) acceleration, max. torsion angle 110°/m

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