Managing director of UK cable cleat manufacturer Ellis, Richard Shaw, recently called on the Institution of Engineering and Technology (IET) to reclassify cable cleats as protective equipment. Energy Source and Distribution discusses the move, which, according to Richard, would eradicate overnight longstanding specification and installation issues that cause myriad of problems in terms of health, safety and system integrity.
The importance of cable cleats is too frequently underestimated, according to Richard, who says instead of being treated as vital elements of electrical cabling installations, they are often lumped in with 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 – this is specifically what cable cleats are designed for,” he said.
“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 electrical installation.
“Unfortunately, it’s not just a question of installing any cleat. It has to be correctly specified for the project in hand. If not, the cables may as well be secured with plastic cable ties. The reason being is different cable cleats are designed to withstand specific forces. Putting this in layman’s terms, the only thing underspecified cleats will do in a short circuit situation is add to the potentially lethal shrapnel.”
One reason Richard gives for the confusion is the cable cleat market is manufacturer driven. Therefore, the choice of product is reliant on third party certification in the form of a short circuit testing certificate, which can be misleading.
“Some manufacturers claim their cleats will withstand a short circuit fault when placed a specific distance apart and can, quite legitimately, provide third party certification to support this,” he said.
“What is often overlooked though is this certificate is only valid for cables with a diameter equal to or greater than the one used in the test. If the cables under consideration are smaller then the forces between them are proportionately greater, even if the fault level and spacing stays the same, which means the certificate is inappropriate.”
Put simply, Richard says you cannot say a specific cable cleat has a short circuit withstand without qualifying the statement. “So instead of claiming a withstand of 150kA you’d need to say a cable cleat has a short circuit withstand of 150kA when securing 43mm cable in trefoil at 300mm centres,” he said.
“The only way of rectifying this is through the adoption of cable cleats as short circuit protection devices – a move that would give them the same degree of importance as fuses or circuit breakers.”
In order to back up his argument, Richard outlines three key points:
1) In the event of a short circuit fault the maximum electromechanical stress between the conductors occurs during the first quarter cycle – i.e. at or before 0.005 seconds (based on 50Hz).
2) Typical circuit breakers and other protection devices don’t trip and interrupt a fault until between three and five cycles (0.06 to 0.1 seconds).
3) In contrast, correctly specified cable cleats earn their crust during the all-important first quarter cycle, ensuring the cables remain intact and, as importantly, operational.
“The reclassification of cable cleats as protective equipment would immediately see electrical cable installations being specified and installed that delivered the necessary level of protection both in terms of excessive temperatures and electromechanical stresses,” Richard said.
Needless to say, change isn’t going to happen overnight. Accordingly, Richard says the onus is on specifiers and engineers to take steps to aid the correct specification of cable cleats.
” The key to this is being aware levels of cable protection can be enhanced by selecting only products that are classified in section 6.4.4 of the International Standard (IEC 61914:2009),” Richard said.
What this means, is the cable is guaranteed to still be intact and operable after a short circuit, as opposed to just the cleat.
“Of course, most specifiers and engineers are extremely diligent when it comes to system design. Where the problems tend to occur is with the buyer. For example, a buyer who sees a specification for 4000 of our Emperor cable cleats may look elsewhere for a better per unit price. But with the specification particular to the project and the product, any change in the type and strength of cleat would result in a change in the numbers required, which in turn will impact on the price,” he said.
“Therefore, if a buyer is intent on changing the specification they need to be educated to look at overall cost as opposed to per unit cost.
“And it is this educational approach that needs to be adopted across the board until such time as cable cleats are reclassified and this dangerous loophole in electrical cable installations is closed once and for all.”