Short-Circuit Rating of Copper Ground Bus

Fault current rating on a ground bus? Fault current ratings on phase bus bars are based upon the bracing of the bus that prevents it from going to ground or shorting against an adjacent bus. Your ground bus should be nowhere near any other bus, and having it go to ground is a moot point.

Ground bus is usually just rated for the thermal capacity of the potential ground current, i.e. the available fault current for the time frame involved, in your case 30 cycles. My last UL test for some new MV gear ended up in the complete melting of the ground bus, but it took 2 seconds, plenty of time as far as they were concerned.

Thank you. I however use alot of ground bars for my designs. What I was wondering is if there is any way to know the allowable fault current for a particular size of ground bar that can be accommodated by it without it melting for say 30 cycles or so.

Not sure if helps but during short circuit testing of LV switchboards a 30A fuse is used to monitor ground currents with the understanding that if it is not opened the amount of ground current has not been excessive