Features

Shaw: correctly specified cable cleats essential

Shaw: correctly specified cable cleats essential



Ellis’ cleat call

The UK manufacturer highlights the importance of cleats as a protection against cable damage and risk to life

01 December 2013

Earlier this year, Richard Shaw, managing director of UK manufacturer Ellis, called on the IET to reclassify cable cleats as protective equipment – a move he said would eradicate overnight longstanding specification and installation issues that cause a myriad of problems in terms of health, safety and system integrity.

He is now repeating this call to the global electrical community.  

“We’ve been banging the drum about the importance of correctly cleating cables for what seems like years. Yet still it feels like we are light years away from reaching a satisfactory conclusion,” Shaw told Gulf Industry.

“In fact, I’m still absolutely staggered by the number of installations I see where cleats have been incorrectly specified and, in some cases, dispensed with completely in favour of cable ties.”

To convey the impact that reclassification of cleats would have, Shaw explained the purpose of cable cleats and why they are so important.

“The importance of cable cleats is frequently underestimated,” he said. “What this means in practice is that instead of being treated as a vital element of any cabling installation, they are lumped in with the electrical sundries and seen as fair game for cost-cutting.

Ellis’ Centaur cable saddle for high voltage cables

“But for an 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 exactly what cable cleats are designed to do.

“Without cleats, 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.

“Unfortunately, it’s not just a question of installing any old cleat. It has to be correctly specified for the project in hand. If not, the cables might as well be secured with plastic cable ties. The reason being that different cable cleats are designed to withstand specific forces, meaning the only thing underspecified cleats will do in a short circuit situation is add to the shrapnel.”

One reason Shaw gives for this worrying level of confusion is that the cable cleat market is very much manufacturer driven. Therefore, the choice of product tends to be reliant on third-party certification – in the form of a short circuit testing certificate – but unfortunately this can be misleading.

He gives as an example the fact that some manufacturers claim a given short circuit withstand at a given cleat spacing and legitimately provide third party certification to support this. What is overlooked though is the fact 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 certificate is inappropriate.

20,000 of Ellis’ aluminium clamps were installed in electrical substations throughout Lusail City, Qatar

“Plainly and simply you cannot say that a specific cable cleat has a short-circuit withstand without qualifying the statement,” explained Shaw. “So instead of claiming a withstand of 150 kA you’d need to say that the cleat has a short-circuit withstand of 150 kA when securing 43 mm cable in trefoil at 300 mm centres.”

“To me the only way of rectifying this whole complex and potentially lethal issue is through the adoption of cable cleats as short circuit protection devices.

“The reason for this is simple – by giving cable cleats the same degree of importance as fuses or circuit breakers nobody would be left in any doubt about ensuring their correct specification.”

In order to back up this argument, Shaw outlines three key points:

• In the event of a short circuit fault the maximum electromechanical stress between the conductors occurs during the first quarter cycle – ie at or before 0.005 seconds (based on 50Hz)

• 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)

• 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.

“What these three points demonstrate is that without properly specified cable cleats, the time, effort and expense spent assembling a circuit breaking system will go to waste as any electrical installation will be irrevocably damaged by electromechanical stresses long before the short circuit protection devices are put to the test,” he says.

To date, this argument, despite its seemingly unbreakable logic, hasn’t gathered the kind of support needed to influence industry regulators to make the change. But rather than admitting defeat, Shaw and his team have continued to focus attention on changing attitudes wherever and whenever they can.

Ellis’ Emperor trefoil cable cleat

CHANGES HAPPENING

“Things are changing slowly, but surely,” he continued. “There are European and international standards relating to cleats where once there were none. More and more specifiers and contractors are ensuring cleats are correctly specified – most notably in HV and EHV cable installations, where ensuring the integrity of the system is absolutely vital.

“And what’s more, this process is being replicated in our key markets. We are enjoying on-going success in the Gulf states, the USA, Australia, Latin America, China, Russia and closer to home in Mainland Europe and the UK, and in every instance contracts are won after we highlight the reasons why cable cleats need to be correctly specified for each and every project.

“Yet for every success I am sure there are others where corners are cut, cleats are underspecified and lives and systems are put at unnecessary risk.

“It’s very much an on-going battle, and it really shouldn’t be.”

Shaw points out that international and European standards are in place to safeguard against incorrect specification. For example, levels of cable protection can be enhanced by selecting only products that are classified in section 6.4.4 of the International Standard. What this means, he says, is that the cable is guaranteed to still be intact and operable after a short circuit, as opposed to just the cleat.

“Yes, the standards are only advisory, but anyone working in the electrical industry anywhere in the world should pay heed to them – they have been developed for a reason and the reason is that electrical cable installations have the potential to kill.

“There is no way of sugar-coating that particular message. They pose a very real danger that the various standards have been developed specifically to eradicate.

“The problem though is the discrepancy between the prescribed course of action and the one that the electrical industry as a whole seems to believe is the right course of action.”

Where to point the finger of blame for what is a complex and difficult problem is hard to do, Shaw acknowledges, but says how to resolve this dangerous situation is straightforward. “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. And, of course, eradicate the risk to life posed by incorrectly cleated cables.”

Ellis designs and manufactures the world’s leading cable cleats. It is the only manufacturer in the electrical industry that focuses solely on cable cleats and its products, all of which are short circuit and third-party tested prior to being brought to market, are specified and installed around the globe.




More Stories



Tags