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It is 200A per phase.
Theoretically on a 200A feeder (ignoring code requirements for breakers) you can power 480 x 200 x 1.732 for a total of about 166KW of balanced load.
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I'm going to feed a transform 400ft away, that is going to supply 8 trailers so what size wire do I need for this 200amp feeder
I think the better question for me to ask would be what size is your transformer in KVA?
If you don't know, what are your anticipated 120/208V loads?
That is going to determine your 480V feeder sizes and the primary and secondary overcurrent protection.
Please let me know so that we can continue.
150 kva 120 /208v
Ok, so you have a 150KVA 480V 3 phase 3 wire to 120/208V 3phase 4 wire transformer?
Any idea of the actual total load from those 8 trailers?
And it's 400 feet from the primary breaker to the transformer?
Confirm that and I'll tell you what you need.
8 trailers and each will have 125 Main
Ok, so that gives you a max theoretical load per trailer of about 36KW. I assume that you won't be seeing anything like that.
For a 150 KVA transformer you need a 250A breaker for primary overcurrent protection. You can run the 400 feet with a single set of (three) 4/0 (90 degree) copper conductors plus your ground. You can put them all in a 2.5" pipe.
A quick volt drop based on likely loads is less than 1.4% so you are good to go there.
On the secondary side you need a 600A breaker for secondary overcurrent protection. You will then need to split that up and distribute it to your trailers. Each run needs an overcurrent device (125A).