Insulation displacement contact technology in moving cable systems

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One of the biggest trends in today’s industries is the move towards fully automated systems. The introduction of ethernet into the industrial environment has been one of the biggest enablers to this, but with organisations under increased pressure to make operational and cost savings, there is demand to increase efficiency and reliability of the communications and cabling systems. Justin Leonard, director at igus, reviews how some of the latest cabling technologies are being used to speed up installation and increase reliability

 

Ethernet and profinet cables with insulation displacement contact (IDC) technology are being used increasingly in industry. However, these cables, which are equipped with 19 wires in dynamic systems, are not mentioned in the relevant EN 60352-3 standard. As such, to prove their reliability Harting and igus have carried out tests on these connections under the conditions set out by the standard to assure electrical engineers that they are dependable, providing long life high performance without failure.

It goes without saying that the cables used for data transmission are extremely important. A cable break or faulty connection point could ultimately lead to the complete system coming to a standstill. Considering that hundreds, or even thousands, of these cables and connections are used in larger-scale systems, every individual conductor and every individual connector must be able to cope with extremely tough service life and fail-safe requirements.

This is made even more difficult to achieve because the cables are exposed to high mechanical, climatic or chemical loads depending on the application.This is true in particular to those applications where the cables move along with moving system components such as in linear and handling axes or robot arms.
What is applicable for the cables is just as valid for the plug-type connections. Constant vibrations or several thousand cycles per shift with a corresponding number of bending and moving processes for the cables must not lead to the individual conductors becoming loose in the terminal.

Wherever any electrical system is installed, and especially in systems where the integrity of low-power signals is critical, electrical terminations must provide high-quality, low-resistance connections between conductors and the termination device. Industry has placed great emphasis on reducing the time required to make terminations while maintaining integrity of the system.

Conventional screw, solder, and cage clamp termination devices all require the insulation to be removed from the conductor to ensure electrical contact. Stripping the insulation to the required length without damaging the conductor takes time and must be accomplished properly.

A reliable alternative to conventional terminal methods is ICD technology. With this technique the insulated wire is forced into a gap which narrows and the flanks of which are formed as blades. The blades cut through the insulation and make contact with the actual wire, which is shaped in the process. When properly done, the connector blade cold-welds to the wire, making a gastight (i.e. non-ageing) connection.

IDC technology’s greatest benefit is installation speed, as the insulation does not have to be removed, the time saving is considerable. Originally developed for office communication and IT network technology, this technology permits simple, time-saving and solder-free connections to be made without special tools. And these are exactly the advantages that industry wants to exploit. Since the requirements here are very high, as described above, lots of detailed development work has been carried out. The materials, for example, have undergone careful scrutiny, the geometry and clamping effect improved and the process intensively simulated at the computer. The objective is to guarantee an even distribution of tension and a constant contact pressure, because it is the contact force which results in conductivity and protection against unintentional loosening of the connection.

There is a standard in place for such connections: EN 60352 ‘Solder-free electrical connections’, Part 3 of which specifies regulations for the product range ‘Solder-free accessible insulation displacement contacts’ and defines ‘General requirements, test methods and application notes’. This standard refers to cables whose conductors are made of one wire or seven wires. In industry, however, cables with up to 19 wires are often used as these are required to guarantee the dynamics required for moving cables.

Therefore, ethernet and profibus cable conductors with 19 wires which are connected using insulation displacement contacts do not comply with the letter of the standard and connector approval is not given under these circumstances. On the other hand, these connections have proved to be reliable in practice without any limitations, even under harsh conditions, and changing to a cable with only one or seven wires instead of 19 would not be recommended on account of the dynamic conditions of use.

igus offers various ethernet and profinet cables in its Chainflex range and manufactures pre-assembled readychain systems for demanding applications using Harting’s RJ45 plug-type connectors of the RJ Industrial 10G series.

To prove their reliability in industry, igus and Harting have tested various 19 wire Chainflex cable systems against the demands made by EN 60352-3.  Equipment from igus’ test facilities and Harting's accredited testing laboratory in Germany were used to test the cables and connectors.

The testing included endurance tests with pre-assembled cable systems which were used according to defined application profiles. Adverse environmental conditions such as frequent changes in temperature and humidity were also simulated, with both cables and insulation displacement contacts exposed to maximum loads.

At the end of every test cycle, the test specimens were cast in synthetic resin – as required by EN 60352-3. Once set, the block was ground and polished until a cross-section through the contact plane was exposed. The central question then was: are the conductors shaped and is there a cold-welded, gastight connection? The position of the wire was also checked to see whether it had moved back out of the original inset and to what extent it can be moved.

Harting and igus were completely satisfied with the outcome of the tests. The polished sections revealed a perfect cold-welded connection even after intensive dynamic use, which promises a long service life if the tests are continued.

As the demand for cost savings, modularisation, and connectorisation fuels the trend toward faster, more reliable connections, IDC connectors are gaining widespread acceptance throughout a variety of industries. Installation and maintenance costs are major factors when commissioning plant machinery and downtime can be very expensive. it can be said that even if the CFBUS cables for ethernet and profinet with their 19 individual wires per conductor are not explicitly mentioned in EN 60352-3, the user can be assured that these cables – especially in combination with the tried-and-trusted Harting RJ Industrial 10G connectors in insulation displacement contact technology – meet even the most stringent of requirements on reliability.