OK quick lesson on capacity to help you see the relationship:
The benchmark for power is watts, or, with AC power,and more accurately, volt-amps (VA).
600 Amps at 480 3 phase=498 KVA of power.
600 Amps at 120/208 3 phase = 215 KVA of power.
My point is not to compare amps at one voltage to another voltage. All depends on the load in power, and the voltage available. 600 amps of 480 volt power is much greater than 600 amps of 208 volt power.
Not sure if this is clear enough to help you undestand, but hard to teach electrical theory is a few sentences.
So, to get 800 amps of 120/208 volt power from a 480 volt 3 phase service you need to install a 300 KVA transformer, which will draw a max of 360 amps from the 480 volt service.
This is practical, and done when necessary. If purchased new, a transformer can cost in the range of $3000.00.
Here is a page from
EBAY,
for a cost of $1500.00.
Along with the transformer, also is needed a 350 or 400 Amp 480 volt distribution circuit breaker, assuming you have a circuit breaker distribution switchboard, the high and low voltage feeder cables, and an 800 Amp 120/208 volt distribution switchboard.
Depending on many variables, the costs for this can be $15-$20K. This should also be designed by an electrical engineer or a contractor capable of design/build projects.
Hope this helps. Get back if you have any other questions.