what is the relationship between the cross section area of bus-bar with current in any switch gear?

Question

what is the relationship between the cross section area of bus-bar with current in any switch gear? How can calculate cross section of area for any bus-bar

Answer 1

Below is a link that provides common busbar dimensions and their ampacities. The factor you did not provide is the allowable temperature rise. The table at the link below provides columns for 30, 50 and 65° C rise over ambient.

The second link provides mechanical properties of the common busbar sizes.