No of bank audit a ca firm can get ??

maximum 3 bank audits per CA firm

In the case of public sector banks, a CA firm can do audit for one bank only and branches allotted may be a maximum of 3 branches.  Size of the branch depending upon the number of parters in that firm.  In the case of private sector banks, number of banks not limited.  If you have influence in those private banks, you can get any number of branches.