|National Grid’s London power tunnels.|
by Tony Conroy, Ellis
arlier this year, Richard Shaw, managing director of U.K. 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 health, safety and system integrity problems.
Now he is 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,” Shaw said, “yet still it feels like we are light-years away from reaching a satisfactory conclusion. 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 favor of cable ties.”
To fully understand Shaw’s concerns and the impact the reclassification of cleats would have, one must understand the purpose of cable cleats. Their importance 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,” Shaw said. “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.”
Shaw said that 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.
|The Zagorskaya pumped storage plant in Russia’s Moscow Region.|
“Unfortunately, it’s not just a question of installing any old cleat,” he said. “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 for the confusion is that the cable cleat market is manufacturer-driven. Therefore, the choice of product tends to rely on third-party certification in the form of a short circuit testing certificate, but unfortunately this can be misleading.
For example, Shaw said, some manufacturers claim a given short circuit withstand at a given cleat spacing and legitimately provide third-party certification to support this. Overlooked, though, is that the quoted short circuit withstand is valid only 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.
“Plainly and simply you cannot say that a specific cable cleat has a short circuit withstand without qualifying the statement,” he said. “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.”
|Ellis’ Emperor trefoil cable cleat.|
The reason, Shaw said, is simple: By giving cable cleats the same importance as fuses or circuit breakers, no one would have a doubt about ensuring their correct specification.
To support this argument, he outlined 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 50 hertz).
- 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 first-quarter cycle, ensuring the cables remain intact and 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,” Shaw said.
|Ellis’ Centaur cable saddle for high-voltage cables.|
To date, this argument, despite its seemingly unbreakable logic, hasn’t gathered the support needed to influence industry regulators to make the change. But rather than admitting defeat, Shaw and his team continue to focus attention on changing attitudes wherever and whenever they can.
“Things are changing slowly but surely,” he said. “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 ongoing success in the USA, Australia, Latin America, China, Russia and closer to home in mainland Europe and the U.K., 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 ongoing battle, and it really shouldn’t be.”
|Cleats being put through their short circuit paces.|
Shaw said international and European standards safeguard against incorrect specification. For example, levels of cable protection can be enhanced by selecting only products classified in section 6.4.4 of the International Standard. In other words, the cable is guaranteed to 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,” Shaw said. “There is no way of sugar-coating that particular message. They pose a very real danger that the various standards, whether international, European or even British 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, but 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,” Shaw said, “and, of course, eradicate the risk to life posed by incorrectly cleated cables.”
Tony Conroy is export director of Ellis, a Yorkshire, England,-based manufacturer that designs and manufactures cable cleats. It is the only manufacturer in the electrical industry that focuses solely on cable cleats and its products. Visit www.ellispatents.co.uk for more information.
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