Selecting a Right Clamp
Most manufacturers do only specify and recommends the short circuit current rating for the selection of cable cleat in kA , but the peak Electromagnetic force generated due to short circuit current is the most important factor for selection of a cable clamp.
Short circuit current is specified in terms of either a “peak” or an “rms” value. The peak current is the maximum current experienced by any of the phases and it occurs once within the first few milliseconds of the start of the fault. The RMS current is a calculated value for the initial cycles of the fault. The relationship between peak current and rms current varies from installation to installation. The forces experienced by a cleat during a short circuit are a function of short circuit current, cleat spacing and the distance between the cable centers (in the case of trefoil arrangements this is the cable diameter). When comparing short circuit test results for different products all three factors must be taken into consideration to compare the relative aggressiveness of the tests.