"What size do i select for Bus Bar rating" The correct one.
It concerns me greatly that you are handling 1,000 amps of power without having a clue what you are doing, and I offer you NO HELP. The life you take may not be your own.
Consult someone who has at least some knowledge of proper sizing and handling of high amperage circuits.
Once again, I find myself confronted by someone with absolutely no applicable experience or education who is obviously completly over their technical head asking us to do their work for them.
Sigh. If this is a schoolwork assignment, read your textbook and class notes and do the problem yourself. The goal of doing the homework is for you to learn and for the teacher to know how much you have learned. If this is a real work assignment, admit to your boss that you do not know how to do this particular task. Building a power distribution capable of 1000A at low or high voltages is not a hobby that people should learn by trial and error.
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"Don't disturb my circles." translation of Archimedes last words
Sam Sam,I agree with the other guys. You need to get out of this business. That aside, this question has been asked a 1000 time. You can count them here