How to calculate copper busbar rating correctly ?, someone say just multiply sectional area to 1.2, someone say just same wire with same or near same size with busbar sectional area, and bla bla bla, what do you think it's true ?, that company says 5mmx40mm copper busbar is rated at 610a
What's correct copper busbar rating for 5mm x 40mm ?

 

Not quite the same as wiring as a busbar is generally in free air!

 

Copper.org/applications has ampacity tables for bus bars. The idea is to calculate the resistance- rho*L/A and then limit the rise to 30 degrees C in most cases. Their table isn't in metric units- but 1/4 x 1.5" which is close on area for a 30 degree rise is 610 amps for 60 Hz. The resistance is 22 microohms per foot, so power dissipated would be about 8 watts per foot- that seems pretty safe. You can do a better calculation with your area, etc but the copper.org tables should give you some guidance.