KA Rating

http://cr4.globalspec.com/search/sitesearch?do=show&sort=textmatchrank&srch=busbar%20sizing&order=asc

K²S² = I²t

Where,

K = Constant

S = Cross section of the bus bar in mm²

I = Short circuit current, in Amperes

t = Duration of short circuit, in seconds

If I understand the original question correctly, you want to know: What is the maximum kA rating that can be carried, through copper or aluminium busbar without excessive heating?

This can be calculated, as a specific temperature rise, which is dependent on the cross section, fault current rating and duration of the fault. However just the conductors thermal capability does not make it suitable, you also need to consider the busbar support material, the phase centres (the distance between each phase), busbar support centres (the distance between supports along the length of the busbar run), and the number of bars per phase. All of these factors will have an impact on the systems capability to withstand the electro-magnetic forces as well as the thermal effect of the short circuit current.

The above can be calculated, however the calculations will only provide a guide and proof of performance can only be achieved by verification by test

Regards

Rob