busbar size

Please check ,generally the final temperature of busbar would be 85 deg C, not the temperature rise.Please inform ambient temperature.

I have answered to such a question earlier reply.

Go to

http://www.copper.org

There are tables for quick sizing copper busbar and the equation for determining bus bar size based on several considerations.

When you supply enough information to solve the problem, you will probably be able to come up with your own answer. You need to consider the power dissipated in the bus bar (current, resistance, and power factor), and the rate power is dissipated from it (type of cooling). You can then design for delta T. Not rocket science.

The industry standard rating for a 4"x1/4" cross section of copper bus is 400 amps.

Old rule of thumb in the switchgear industry has been 1000 amp per 1 sq. in. of buss. 3ka ought to be at least 3x 1/4x 4 Newer tables will show 1200ish but ... 1/4 by 4 is 1000amp.

http://www.stormcopper.com/design/Ampacity-Quick-Chart.htm