Cable Sizing 4000A

[eanton22]

So I am feeding cable from a MV swgr to a 4.16kv to 480V transformer.
Breaker size is 4000A

Can someone please show me the math behind sizing cable to 4000A??

Let's say for example a 1/C #750 kcmil (tray) has an ampacity=630A.

if we use 3 1/C #750 kc mil per phase, the math would be:

3*630A = 1890A

Since we have have three phases

total ampacity would be 3 *1890= 5,670A.

Is the above correct?

Please advise.

 

[iwire]

Each phase would have to have 4000 amps of capacity.

Ten 600 Kcmil copper conductors per phase is a fairly common way to get 4000+ amps of capacity.