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Chris Lloyd, sales and marketing manager for Spelsberg UK, explains the strengths and weaknesses of the various cable entry options and discusses the latest developments.

When specifying an enclosure for electrical applications, one of the key considerations has to be cable entry.

The cable entry points of an enclosure can help to determine the overall level of ingress protection (IP) provided against the external environment as well as cable retention force and installation speed, all the while balancing utility with cost.

Recent developments in materials, moulding technology and push-fit grommets have changed the options that are available, providing a far more specialised solution for a variety of applications.

‘Making the right choice of enclosure and entry method can make the difference between a profitable job and a loss, as well as guaranteeing the all-important safety of installers and end users,’ said Lloyd.

With new ‘moulded-in’ entry methods now on the market, offering extremely fast entries, and traditional cable glands being replaced in some instances by lower-cost fast-fit grommets, it is essential to know when to specify the right solution for any given application.

For example, by far the most common cable entry method is traditional cable glands fitted to the body of the enclosure through knock-outs.

While this option offers a safe choice, what a lot of people do not realise is that they are often over-specifying and that this can increase costs and installation times, as well as making maintenance more time consuming down the line.

Push-fit cable entries have become increasingly popular as plastic moulding technology has advanced.

Enclosure manufacturers regularly use two types of material moulded into one box, providing rigidity in the walls and soft, flexible membranes to allow cables to be pushed through, but still offer a good IP rating, protecting from moisture and physical intrusions.

Cable retention force, however, is lower than with other alternatives.

If an enclosure is going to be used in a clean, dry and well-insulated environment, only lower levels of IP are needed.

In these situations, both the enclosures and the wires are likely to be well secured in their position, so there is little need for high cable retention.

If there are a number of enclosures to be wired, then using cable glands will be time consuming and unnecessary.

Many enclosures, such as the A-Box from Spelsberg, are available with a flexible membrane that provides a seal by pushing the end of the cable through the centre nipple.

As the membrane stretches, the point of greatest extension opens and allows the cable through.

The inverted seal grips the cable and provides the fastest entry seal so far possible.

As IP and cable retention are not large concerns, this method is ideal for reducing installation times and costs; in the event that re-wiring is required in the future, the old wire can simply be pulled out and the new wire inserted.

There are a number of membrane plug/grommet products available that offer sealing up to IP67 and are very fast to use.

As a grommet, they are a push-fit design both to install and to feed the cable through.

Recent grommet designs will allow for a variety of cable/conductor widths and are resistant to vibration.

There are fast-fit grommet seals available that clip into standard drilled and knockout holes that provide positive cable retention.

According to Lloyd, the best of these, the Klikseal from TST, is moulded using two materials: a softer compound for the body/seal and a stiffer inner material that applies positive clamping and cable retention.

The Klikseal provides most of the advantages of a cable gland while avoiding many of its disadvantages, including its high purchase cost.

The main advantage is the fitting time for a Klikseal; this can be as low as 10 seconds, compared with minutes for a cable gland.

The reduction in fitting time can speed up installation and reduce costs on large installations and OEM assembly lines.

Despite the advantages of quick-fitting seals and grommets in many applications, there are still some situations where the most appropriate cable entry method is the clamped, dome-top cable gland.

These glands are designed to provide an aesthetically pleasing and professional look to any installation.

A number of variations of this type are available in both nylon and metal, but the salient features that ensure best performance to the traditional stuffing gland are in its construction.

The cable is fed through a sealing ring that is placed in an ‘iris’ that closes onto the sealing ring, clamping the cable and forming a high IP seal as the dome top is screwed down.

This forms an IP68 seal around the wire, meaning that the enclosures can be fully submerged without fear of ingress, as well as creating very high cable retention, alleviating any risk of connections failing owing to pressure on the wire.

There are many cable entry options available, all of which carry different benefits to the user.

Choosing the correct solution can save money and time at the point of installation and during future maintenance.

When specifying for a specific application, it is important to speak to an expert who can recommend the ideal product.

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