Talking Cable Cleats

Talking Cable Cleats

Who would have thought that something as simple looking as a cable cleat could cause so much debate?
The recent introduction of both European and International standards, meant that cleats became one of the hottest topics in the electrical industry, but despite this prominence, their role in electrical installations is still not fully understood. Therefore, we decided to clear things up by asking the expert – step forward Richard Shaw, managing director of Ellis Patents. 
Cable cleats explained
 “For an 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 the job that cable cleats are specifically designed to do. Take them away and the dangers posed by a short circuit are plentiful – costly damage to cables and cable management systems, plus the risk to life posed by incorrectly or poorly restrained live cables.
And it’s important to bear in mind that it’s not just the use of a cleat that is vital, but the use of a correctly specified cleat. Because all an underspecified product would do in a short circuit situation is add to the shrapnel.
The key issue surrounding cable cleats is that their importance has been, and still is, severely underestimated. Therefore, instead of being treated as a vital element of any cable management installation they are simply lumped in with the electrical sundries.
What this means in practice is that even if suitable products are specified, they are still seen as fair game for cost-cutting when it comes to companies seeking to keep within tight budgets. This is a potentially dangerous practice that, if allowed to continue, could lead to the wholly unnecessary loss of a life.
Furthermore, there’s a common misconception that electrical cables are fully protected by circuit breakers, but that simply isn’t the case. In the event of a fault, the forces between cables reach their peak in the first quarter cycle, while circuit breakers typically interrupt the fault after three or even five cycles. And by this stage, if the cleats are underspecified, the cables will be long gone.
The introduction of (IEC61914 – 2009) and European (EN50368) was a huge boost for everyone associated with cable cleats. They helped provide global recognition of the need for secure cleating in electrical installations, but they still fall some way short of ensuring the cleat is universally understood and used correctly. The main reason being that both standards are advisory rather than regulatory, meaning the onus is on the manufacturer to self certify their products – a situation that has led to a market awash with a mish-mash of products of differing quality, which in turn means further confusion for specifiers and installers.
Solving the cable cleat issue
People need to be made fully aware of what exactly happens when cables aren’t correctly restrained. We do a lot of short circuit tests and a good way of explaining what happens to the cables is to look at the difference between those that are correctly restrained and those that aren’t.
In recent tests we did with our American distributor, kVA Strategies, we performed three short circuit tests on 3 x 1/C-777kcmil, 2kV marine cables at 59kARMS in trefoil formation. One test was conducted on cables tied with 1/2" wide stainless steel cable ties, while the other was conducted on cables restrained by our Emperor trefoil cable cleats. During the short circuit the mechanical forces between the cables exceeded 4,500 lbs/ft.
After one short circuit, the cables restrained with the metal cable ties were damaged beyond repair – suffering multiple tears in the cable jackets and insulation, as well as evidence of electrical arcing. In fact, the metal cable ties catastrophically failed before the first quarter cycle current waveform peak, ejecting the ball bearings from the cable tie buckles with sufficient velocity to lodge deeply into the plywood test bay walls. The subsequent cable thrashing also severely damaged the cable tray.

In contrast, the correctly restrained cables were subjected to not one, but two successive short circuits and after careful inspection no damage was found. In fact, the testing lab team stated that the cables still passed the required IEC voltage withstand test and so could continue to be used at full-load.
In an ideal world compulsory third party certification would clear up all the problems. Unfortunately, this is open to misinterpretation and possible abuse because the quoted short circuit withstand, which is seen as the indicator of a cleats suitability for a project, is only valid for a cable diameter equal to or greater than the diameter of the cable used in the test.
Therefore, if the project in question uses smaller cables than those referred to in the test (and the fault level and spacing is the same) then the force between the cables is proportionally greater, meaning the certificate is inappropriate and the cleats will not provide the protection they are installed to give.
As a result, this means that at present the only tried and tested way to ensure correct cleating is through project specific testing – a process that we currently offer customers that means they can install our cleats with complete confidence. 
Cable cleat knowledge
From a wholesaler’s point of view, knowledge about the different types of cleats, what they are used for and how they are installed is every bit as important as knowing why they are needed. But, as I’m sure you’d expect by now, this knowledge is far from simple.
Take the cleats themselves. There is a huge variety available, and all of them are designed for different installations. For example, our Emperor cleats are recommended for the highest short circuit fault duty applications. Meanwhile, our Centaur cleats are designed specifically to restrain high voltage cables up to 400kV with a diameter range of 100 to 160mm.
In order to ensure the correct cleat is used the best course of action is always to consult the manufacturer. By giving them information concerning the installation environment, mounting structure, cable configuration, peak short circuit fault level and cable diameter, they should be able to advise on the most suitable cleat and the spacing at which it should be installed.” 

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