OCPD & Wire Size

[Alwayslearningelec]

I’m being asked to provide 250A and 200A of power( they need that load/amperage in the field for temp power) in two different locations from two different panels.
Panels are 277/480v and will feed a step down xfrmr which will feed a120/208v panel.
They are telling me to price a new 200A and 250A breaker in the new 277/480v panels.
My thinking is that I don’t need that size breaker to feed the 277/480v step down xfrmr.
I could install either a 75 or 112kva xfrmr with the appropriate primary OCPD/wire and this would deliver power needed on the secondary side in the field.

Is my thinking correct? Thank you

 

[drktmplr12]

what is the load?

 

[Alwayslearningelec]

what is the load?

I requested more info and I'll provide. I'll also explain what I think is required.


What doesn't make sense is they say there's a 250a spare breaker @ 277/480 they want us to use to feed the temp power dist center which will comprise of the following:

1. 277/480v panel
2. step down xfrmr
3. 120/208v panel

They want 150A available at the 277/480v panel and they want 100A available at the 120/208v panel.
the confusing part is if those are the loads or size of the panel they want.

So my thinking: Working a little backward..

1. I would need a 45kva xfrmr to satisfy the 100A at 120/208v to feed the 100A panel. This would require 3p 80a breaker in the 277/480v panel to feed the primary side of the 45kva xfrmr and then I can feed the 100A panel from the secondary side but I'd really need a 150A MCB panel???
2. So what size 277/480v panel would I need to feed 200A worth of loads from the temp 277/480 panel and then the 45kva xfrmr for the 150A MCB panel from that same 277/480v panel?? Again the question is whether the 250A is true loads or just size( 150A and 100A) of MCB panels they want. IS that correct?

So if I was to give them a 250A main feeder from the 277/480v spare breaker to the temp distribution equipment described above would that provide enough power for 200A @ 277/480v and 100A at 120/208v?

Hope this makes a little sense.