Don’t judge a report by its cover

Cable cleat manufacturer, Ellis recently warned that incorrect interpretation of short-circuit test reports was leading to inappropriate cleats being specified and installed. Managing Director, Richard Shaw explains why this situation is putting vital electrical installations and lives at unnecessary risk.

The role of the cable cleat in any electrical cable installation is of paramount importance in terms of safety and system integrity. They are there to prevent costly and dangerous damage to cables and those around them in short circuit situations. In fact, and as I’ve often said before, the only thing underspecified cleats do in a short circuit situation is add to the shrapnel.

Historically, this message, despite its hard-hitting nature, has never been fully appreciated and so rather than being treated as an integral part of an installation, cleats have too frequently been lumped in with electrical sundries and seen as fair game for cost-cutting.

This mindset is slowly changing, helped along by regulations governing the use of cleats (EN50368 / IEC61914), but there is still a long way to go before the finishing line comes into sight.

Third party testing

Ironically, one of the issues clouding the picture is something I have long championed as a tool for resolving the problem. That is, the use of third party short circuit testing to prove the suitability of a cleat for a particular installation.

Third party short-circuit testing is the only way to effectively prove a cleat does what it claims to and is something we carry out as standard on any new product. Previously, I’ve said the widespread adoption of our approach would clear the cleat picture up once and for all. But today, it seems that isn’t enough to resolve things.

Firstly, there’s the fact that some cleats simply aren’t what they claim to be. Sometimes this is down to issues surrounding manufacture, but more often than not it’s short-circuit withstand claims that simply don’t stand up to scrutiny, which means the cleats are likely to be wholly unsuitable for installations they claim to be designed for.

Then there are the issues generated by the reports of properly tested products. Short circuit reports in general tend to be lengthy, in-depth documents and so a lot of people will be tempted to quickly refer to the headline figure rather than properly reviewing the entire document.

The danger with this is that some will take it to mean that the products tested deliver the same level of short-circuit withstand irrespective of the installation. For example, a recent report I was given showed a product withstanding a peak short-circuit of 138kA, but on full reading it became clear that the test rig was set up with four trefoil circuits in parallel and that, under these circumstances, although the overall fault level was 138kA, each of the four trefoil groups only saw a quarter of the fault, equivalent to 34.5kA.

Worryingly, the example is just one of many and the moral of this story is clear – don’t judge a short circuit test report by its cover.

Analyse reports

The story clearly highlights the need for third party test reports to be carefully analysed prior to being acted upon. Of course, this puts the onus on the specifier or contractor to do this work, but as a leading manufacturer we feel we should play a far more active role in ensuring correct specification of our products.

In order to correctly interpret a report those with specification responsibility should ask two simple questions. Firstly, is the product tested the same as the product being offered? And secondly, is the test installation similar to the project installation? For example, a test of three single conductor cables in parallel secured with single cable cleats cannot be compared with a trefoil installation secured with trefoil cleats. This can all then be backed up by calculating the forces experienced by the cleat during the test and comparing it with the anticipated force the nominated cleat would see in the proposed installation.

Admittedly, this sounds complex and many will breathe a sigh of relief when they hear there is an easier way round it.

Absolute guarantee

Project specific testing removes the opportunity for any misunderstanding by testing a particular product to ensure it can stand up to the requirements of a specific project.

This is third party testing at its most extreme, and at present it’s the only way to deliver an absolute guarantee that the cleat being installed is suitable for the installation.

It does though need to be noted that the certificate this delivers is specific to the installation, its fault level, spacing and cable configuration. A cleat’s short circuit withstand, which is seen as the indicator of its 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. So if the project in question ends up using smaller cables than those referred to in the test 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.

This could then be supported by the adoption of cable cleats as short circuit protection devices, which would automatically give them the same degree of importance as fuses or circuit breakers.

The argument for this isn’t as outlandish as it first sounds. In the event of a fault, the forces between cables reach their peak in the first quarter cycle, which is the point that cleats earn their crust. In contrast, circuit breakers typically interrupt the fault after three or even five cycles by which time, if the cleats are underspecified, the cables will be long gone.

Turn the tide

It does seem that the process of overhauling perceptions of and attitudes towards cable cleats is far more difficult than it should be. On the one hand it seems to be being hindered by those who seem intent on making sales through the exploitation of the lack of widespread knowledge about cleats and short-circuit tests. While on the other, there still seems to be a strong undercurrent of those who are averse to allocating a suitable budget allocation to cleats – despite the fact they save lifetime cost and deliver safety and peace of mind.

In a perfect world, the widespread adoption of project specific testing and the adoption of cleats as circuit protection devices would resolve every issue. And while I am hopeful this will eventually happen, I’m realistic to know if won’t occur overnight. Until then myself and everyone else connected with Ellis will continue to bang the drum for cable cleats wherever and whenever we are given the opportunity and slowly the tide will continue to turn.

www.ellispatents.co.uk