Why is short circuit testing important for cable cleats?

Why is short circuit testing important for cable cleats?

Conducting a short-circuit test is the only reliable way of proving that a cable cleat is capable of withstanding a specific set of fault conditions.

We always recommend that any claims of cable cleat strength should be supported by a short-circuit test carried out in an independent and accredited laboratory and appropriately certified.

Specifiers, consultants and engineers should also request, as standard, a complete test report that includes before and after photographs, and a table of results and conclusions.

This practice is becoming commonplace, but prior to the publication of the international standard IEC 61914 many cable cleats were not tested, and those that were had no standardised testing method by which to gauge success or failure. As a result, test results were open to a wide range of differing interpretations.

IEC 61914 has provided a standardised method for conducting a short-circuit test and a definition of the criteria for a pass. It does though allow for a significant degree of latitude and so caution must be employed when interpreting results. Note should also be taken of the full report as opposed to just its headline page.

EXAMPLE

Two manufacturers have tested cable cleats to the international standard IEC 61914 and both claim their cable cleat is capable of withstanding a peak short-circuit current of 140kA.

Manufacturer ‘A’ conducted a test using a 35mm cable cleated at 600mm centres

Manufacturer ‘B’ conducted a test using a 45mm cable cleated at 300mm centres

Your system peak fault level is 60kA, you are using a 30mm diameter cable and you wish to cleat at 1200mm centres.

Are both cleats suitable? No.

Using the formula from The international standard IEC 61914 (provided and explained in the following section) the force each cable cleat was subjected to was:

Manufacturer ‘A’ – 57kN

Manufacturer ‘B’ – 22kN

You require – 24kN (min)

Manufacturer B’s product does not meet the requirement.

 

ALWAYS REMEMBER: Ellis cable cleats are all short circuit tested and will meet the specific project requirements

There is a major difference between the short-circuit withstand requirements of a cable and the short-circuit withstand of a cable cleat.

The former is concerned with cable degradation as a result of temperature rise (thermal stress heating), while the latter is concerned with cable retention as a result of electromechanical forces.

Typical installation specifications that have been derived from the thermal withstand of the cable would require a short-circuit withstand of 63kA for 1 second or 40kA for 3 seconds.

A short-circuit test for a cable cleat does not consider this heating effect, and instead concentrates entirely on the destructive electro-mechanical forces at peak, followed by a short term decaying RMS.

The international standard IEC 61914 requires a short-circuit test duration of just 0.1 second. This equates to five complete cycles, by which time the true strength of a cable cleat will be known.

Learn more about our cable cleats on our downloads page – https://www.ellispatents.co.uk/downloads/.

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