Plant downtimes and production problems due to electromagnetic interference - caused by wireless communication devices, electric motors or frequency converters, for example - are not uncommon. Production downtimes and rejects have consequences such as supply bottlenecks, loss of image and increasing costs, as well as a great deal of effort to find the 'gap in the system' - i.e. the source of the fault.

Control cabinets and enclosures can be shielded against electromagnetic interference with appropriate design measures. However, where cables are routed through the enclosure wall, there is a gap in the shielding through which electromagnetic waves simply 'slip through'. To reliably close this gap, shielded cables are securely contacted with EMC cable glands and thus integrated into the overall EMC concept. In this way, interference does not penetrate either out of or into the housing.

For the user, ease of installation and installation safety of the EMC components are of great importance, as the former saves time and costs, while the latter ensures high operational safety of the overall installation. However, the attenuation values that can be achieved are at least as important for the user.

Higher damping and easy installation

The possible shielding attenuation values of an EMC cable installation depend heavily on the care taken during installation. For example, changing the structure of the braided shield when stripping the cable or expanding it can create shielding gaps that allow electromagnetic interference to slip through during operation.

Cable routing supplier Pflitsch therefore takes a special approach in its 'Uni Dicht' and 'blueglobe' series to achieve high process reliability and reliable attenuation properties: The principle uses closed spring washers in the cable glands and makes contact with the cable's shielding braid all around instead of just at certain points. This procedure significantly increases the shield attenuation values.

At the same time, installation is simple and safe, as users only have to remove the cable sheath at the contact point where the braided shield is to be contacted later. When the cable is inserted into the cable gland, the spring force ensures reliable contact even with non-circular cables. The principle also means that the cable shield can be fed into the switch cabinet and only needs to be cut to length directly at the connection point. This achieves maximum shielding attenuation and avoids unnecessary coupling of useful signals with interference signals.

Safe 360° contacting

As the braided shield of the cable does not have to be expanded at the contact point, but is securely contacted via the 360° triangle spring and only connected to earth in the switch cabinet, the EMC cable glands are easy and safe to install.

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With the 'Uni Iris' cable gland, a spring washer ensures 360° contact with the exposed cable shield. When the pressure screw is tightened, it is pressed securely against the braided shield on all sides and ensures a good electrical transition.

A triangular spring is used in the 'blueglobe' series. This contact element enables reliable and fast installation with above-average attenuation values. Once the braided shield is exposed, the cable can simply be pushed through the triangle spring. It immediately wraps itself securely around the braided shield and provides EMC protection without the need to tighten the pressure screw. With this system, the shielding is mechanically separated from the seal, as no great forces act on the contact point when the pressure screw is tightened and the shielding braid remains in tact. The design of the spring prevents it from getting caught in the braid during assembly or disassembly. With its geometry, it ensures large-area, low-resistance and durable 360° contacting - even with non-circular and off-center cables.

In industrial data technology applications, this EMC cable gland offers maximum signal reliability with over 80 dB at 100 MHz and 65 dB at 1000 MHz. The accredited GHMT test laboratory has also tested and certified the 'Tri' in accordance with Cat. 7A. Stainless steel solutions designed to EHEDG standards are also available for applications where hygiene or design are required.

Higher current carrying capacity than the shielded cable

With the 'Uni Iris' cable gland, the Iris spring is pressed securely against the cable shield by two cones when the pressure screw is tightened. The braided shield remains intact.

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In addition to HF attenuation, the current carrying capacity - i.e. the ability of a component to carry a certain continuous current - is an important criterion for an EMC cable gland. In the event of malfunctions, incorrect installation or lightning strikes, high currents can flow through the cable shield and the cable gland. The voltage drop at the contact resistors of a cable gland also generates a certain power loss due to the current flowing through the cable shield.

As there is no test standard for this case, Pflitsch has implemented a practical test setup in its in-house test laboratory, in which an increasing current up to a maximum of 100 A is applied to the cable shield and the temperature development in the cable gland up to +60 °C is determined. The result: As a rule, the 'blueglobe Tri' achieves a higher current-carrying capacity than the shielded cable, thus offering the necessary safety in every case. In practice, however, this should be verified in the respective installation.

Combination for customized EMC solutions

Walter Lutz works as a freelance journalist for PRservice in Haiger.

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In order to save mounting space, special customized solutions are sometimes required, as the space for cable entries is limited in compact system enclosures. If a user then has to insert various EMC cables into the enclosure, the lack of mounting space can lead to bottlenecks. To solve this problem, Pflitsch combines functions from the two cable gland series mentioned above.

The 'Uni Dicht' range includes the multiple concept, which allows several cables - even with different diameters - to be reliably fed through one cable gland. Behind the sealing insert is a precisely fitting metal washer, which is manufactured exactly for the cable diameters used by the user. The shield of each cable is securely contacted in this disk via a 'Tri' spring. A circumferential 'Iris' spring ring ensures reliable contact with the inserted washer in the cable gland. As the 'Uni Dicht' is available up to size M120, it is possible to integrate several EMC cables with a diameter of 5 mm to 20 mm (including braided shield).

Contact multiple screens safely

In modern electronics, the cable shield often fulfills several tasks: On the one hand, it significantly determines the cable impedance and, on the other, it is intended to prevent signals from being coupled out and/or in. Unpleasantly, unwanted potential equalization can take place via the braided shield.

This is why there are special cables with multiple shields. Making EMC-compliant contact between these shielded cables and the electronics in the housing is a challenge, but one that can be overcome with the extended 'blueglobe Tri' and its two triangle springs positioned one behind the other: the first spring is used to connect the outer shield of the cable directly to the outside of the housing, while the second spring connects the inner shield to the housing with low impedance. The possible third shield can then be routed to the ground test point in the switch cabinet and connected there. This solution achieves a shielding effect of better than -80 dB at frequencies up to over 1 GHz. Furthermore, the current-carrying capacity is doubled, which is important for frequency converters and in the field of electromobility, for example, where high-frequency shielding currents of more than 25 A are nothing out of the ordinary.