Calculating Forces Between Conductors During a Fault
The international standard IEC 61914 includes a formula in Annex B that allows designers to calculate the force between two conductors during a fault. If the strength of a particular cable cleat is known, the optimal spacing of the cable cleat along the cable to restrain the force created by the fault can be determined.
Understanding Cable Cleat Strength
The strength of a cable cleat is often determined using a mechanical tensile test. However, the results of such tests may be misleading because the force is applied in a slow and controlled manner, which does not replicate actual fault conditions.
Differences Between Mechanical and Short-Circuit Tests
In a short-circuit fault, the forces are applied almost instantaneously and oscillate in every direction. Experience shows that a cable cleat that survives a mechanical tensile test at a given force will not necessarily survive a short-circuit test, even if the forces are the same.
Consider the properties of glass, which is immensely strong under tension but can fail brittlely when impacted.
Conclusion
For accurate assessment and design, short-circuit testing is crucial. Learn more about our cable cleats on our cable cleats page.