Ultra-fine stranded wire: necessity or misconception in dynamic applications?

The stranded wire must be very finely stranded, otherwise it will not last in the chain", or "I need a Class 6 conductor for the robot cable" - you often hear statements like this from users. They often follow a core rupture that has led to a machine standstill. The consequences are often a loss of production or high repair costs.

But what exactly is a stranded wire?

A conductor is the part of an electrical cable that is responsible for the current flow - in other words, the copper inside, which is surrounded by insulation material to prevent the current from jumping over to neighbouring cores. If the conductor consists of several wires, the technical term is stranded wire. Several wires together form a stranded wire. A stranded wire wrapped in insulation ultimately forms an electrical core.

Conductor classes and their significance for different applications

There are different conductor classes. The different applications for which cables are required naturally place different demands on flexibility and durability. An underground cable, for example, is moved much less frequently than a measuring cable in physics lessons. The flexibility of the conductor must therefore vary depending on the area of application in order to take factors such as feel, connection technology, processing and costs into account.

The IEC/DIN EN 60228 (VDE 0295) standard classifies conductors into four categories in order to roughly determine how flexible the conductor should be. The classification is based on the diameter of the individual wires and their number. This means that a conductor nominal cross section - important for the current flow - can be achieved in different ways. It can consist of a solid single wire or be composed of many small wires that together provide the same cross-sectional area.

The standard provides for the following categorisation:

• Class 1: solid
• Class 2: stranded
• Class 5: fine-wire
• Class 6: very finely stranded

Conductor class in permanently moving applications:

It is obvious that a solid conductor is not suitable for continuously moving applications such as energy chains or robots. However, the conductor must not be too fine-wire either.

In numerous tests conducted in our in-house test laboratory, we have established that the wires of a stranded wire must not be too fine. If the wires are too fine, they stretch under tensile forces when bent in the outer area of the core. If the bending is stopped, small wire loops form as the copper does not contract again. The constant repetition of the movement results in more and more of these wire loops, which can ultimately lead to the core breaking. The optimum design for moving applications is therefore not the one with the thinnest wire, but the one in which the wire thickness is matched to the respective conductor nominal cross section - be it 0.5mm², 0.75mm², 1.0mm² or 1.5mm².

With us, you do not have to specify the conductor class, because we already install the optimum conductor for your requirements in the core. Simply let us know which mechanical specifications your cable needs to meet and we will select the right product for you from our catalogue product range. The best way to do this is to use our online chainflex price check.