What is the validity period of the temperature ranges specified for the cables and wires in our catalogue?
The average service life of cables and wires is affected not only by the mechanical and chemical load, but also by the operating or ambient temperature. The temperature range, which generally refers to the quality of the insulation or outer sheath material, largely depends on the following two factors:
• Fixed cable installation: The cable is not subjected to additional mechanical load as a result of flexing. Temperatures are generally lower in the minus range and often higher in the plus range.
• Highly flexible use or occasional flexing: Flexing subjects the cable to a higher mechanical load than in the case of fixed installation. Temperatures in the minus range are considerably higher than with fixed installation, while the temperatures in the plus range are also usually reduced.
Virtually all catalogue specifications concerning the temperature ranges of our ÖLFLEX® and UNITRONIC® cables are based on a permanent temperature over 20,000 hours of operation – with just a few exceptions, as it is standard in the machinery engineering industry. To verify this, intersection graphs (Arrhenius plots) are created on the basis of long-term, normative tests. The established results can then be used to determine an approximation of how long and at what temperature a specific polymer can be used. The starting point of this process is always formed by the mechanical elongation and strain value of the polymer in new condition. If, after a specific test duration, the oven-aged plastic retains at least 50% of the elongation and elasticity properties that it possessed in new condition it is classed as resistant to the relevant temperature. Cables are often used over many decades without encountering any problems. Particularly in the case of static installations without cable movement, the mechanical properties are of relatively minor significance.
There are also differences in the various normative test methods used to establish continuous operating temperatures. The automotive industry often employs ISO tests, in which much higher temperatures are determined for the same polymer compound than in VDE, DIN or EN testing standards. These tests often determine a continuous temperature of +120°C for some plastics, where our catalogue only specifies +90°C for the same material. While this is partly due to the different test methods employed, it can also be attributed to the fact that the automotive sector often considers only 3000 hours a sufficient continuous temperature period compared to the 20,000 hours used in the machinery engineering industry.