WCA November 2013

Understanding the importance of cable cleats By Richard Shaw, managing director, Ellis The costs associated with the construction and maintenance of any transport infrastructure project are exceptionally high – as is the pressure to maintain a safe and reliable environment for those using the transport services they provide access to. Therefore, it would seem extremely remiss if one signifcant installation aspect was frequently neglected. According to Richard Shaw, managing director of British cable cleat manufacturer Ellis, there is one such aspect – and worryingly it is related to electrical power cable installations. The importance of cable cleats is frequently underestimated. What this means in practice is that instead of being treated as a vital element of any electrical cabling installation, they are lumped in with the various sundry items and seen as fair game for cost-cutting. But for any electrical installation to be deemed safe, cables need to be restrained in a manner that can withstand the forces they generate, including those generated during a short circuit, and this is specifcally what cable cleats are designed for. Without them, the dangers are obvious – costly damage to cables and cable management systems, plus a risk to life posed by incorrectly or poorly restrained live cables. All of which is in stark contrast to the stringent safety requirements of any transport infrastructure project, especially those that see thousands passing through each and every day. Unfortunately, it is not just a question of installing any old cleat. It has to be correctly specifed for the project in hand. If not, the cables may as well be secured with plastic cable ties. The reason being that different cable cleats are designed to withstand specifc forces. Putting this in layman’s terms, the only thing underspecifed cleats will do in a short circuit situation is add to the potentially lethal shrapnel. One reason for this worrying level of confusion is that the market is very much manufacturer driven. Therefore, the choice of product tends to be reliant on third party certifcation – in the form of a short circuit testing certifcate – but unfortunately this can be misleading. For example, it is not uncommon for manufacturers to claim a given short circuit withstand at a given cleat spacing and legitimately provide third party certifcation to support this. However, the overlooked fact is that the quoted short circuit withstand is only valid for a cable diameter equal to or greater than the diameter of the cable used in the test. If the project in question uses smaller cables (and the fault level and spacing is the same) then the force between the cables is proportionally greater and the certifcation inappropriate. Plainly and simply, you cannot say that a specifc cable cleat has a short circuit withstand without qualifying the statement. So instead of claiming a withstand of 150kA you would need to say that a cable cleat has a short circuit withstand of 150kA when securing 43mm cable in trefoil at 300mm centres. To me, the only way of rectifying the issues surrounding cable cleats is through their adoption as short circuit protection devices – a move that would give them the same degree of importance as fuses or circuit breakers and leave no one in any doubt about ensuring their correct specifcation. The reasoning behind this suggestion is simple. In the event of a fault, the forces between cables reach their peak in the frst quarter cycle, which is the point that cable cleats earn their crust. In contrast, circuit breakers typically interrupt the fault after three or even fve cycles by which time, if the cleats are underspecifed, the cables will be long gone, meaning the expensively assembled circuit breaking system will never be given the opportunity to be tested.

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Wire & Cable ASIA – November/December 2013