Proving Cable Cleat Strength: The Importance of Short-Circuit Testing
Conducting a short-circuit test is the only reliable method to verify that a cable cleat can withstand specific fault conditions. We always recommend that claims of cable cleat strength be supported by a short-circuit test conducted in an independent and accredited laboratory, complete with appropriate certification.
Standardized Testing and Certification
Specifiers, consultants, and engineers should request a comprehensive test report that includes:
- Before and after photographs
- A table of results and conclusions
Although this practice is becoming more common, prior to the publication of the international standard IEC 61914, many cable cleats were not tested or lacked a standardized testing method. This led to varying interpretations of test results.
IEC 61914 has established a standardized method for conducting short-circuit tests and defining pass criteria. However, some latitude in interpreting results remains, so it’s important to review the full report rather than just the headline page.
Example Scenario
Two manufacturers claim their cable cleats can withstand a peak short-circuit current of 140kA, but the details of their tests differ:
- Manufacturer ‘A’: Tested using a 35mm cable cleated at 600mm centers
- Manufacturer ‘B’: Tested using a 45mm cable cleated at 300mm centers
Your system has a peak fault level of 60kA, you are using a 30mm diameter cable, and you wish to cleat at 1200mm centers. Are both cleats suitable? No.
Using the IEC 61914 formula, the force each cable cleat was subjected to was:
- Manufacturer ‘A’: 57kN
- Manufacturer ‘B’: 22kN
Your requirement is 24kN (minimum), so Manufacturer B’s product does not meet the requirement.
Understanding Short-Circuit Withstand Requirements
There is a significant difference between the short-circuit withstand requirements of a cable and those of a cable cleat:
- Cable: Concerned with degradation due to temperature rise (thermal stress heating)
- Cable Cleat: Concerned with cable retention due to electromechanical forces
Typical installation specifications derived from thermal withstand of the cable may require a short-circuit withstand of 63kA for 1 second or 40kA for 3 seconds. However, a short-circuit test for a cable cleat focuses on the destructive electro-mechanical forces at peak, followed by a short-term decaying RMS.
IEC 61914 specifies a short-circuit test duration of just 0.1 seconds, equating to five complete cycles, which is sufficient to determine the true strength of a cable cleat.
Conclusion
Nasco cable cleats are all short-circuit tested and will meet specific project requirements. Learn more about our cable cleats on our cable cleats page.