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New service, existing transformer....will this work? This is kinda long....

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Here is the deal......

I have a customer with a existing pad mount transformer that feeds a 3000A 480V service. This transformer has (2) 3" pvc conduits that are spares to just out of the xfmr pad.

The customer is putting a fertilizer blender in, and we plan to utilize these existing spare conduits out of the XFMR. POCO (duke energy) is good with this. There is spare lugs in the XFMR also.

Here is the tricky part......maybe.....

The customer wants to run more service capacity to the area the fertilizer blender is in than just what is needed for the blender. The blender is 60HP total (I think, waiting on cutsheets) and has a 200A disconnect on it (again, so I am told, waiting on cutsheets)

So, assuming the mixer requires 200A, we will likely run a 400A service to the general area, build a rack with a 400A FUSIBLE disconnect and split it up from there as needed.

The (2) 3" spare conduits from the xfmr are just turned up and capped off right now. I intend to set a pull box (quazite) over them and run a 4" to the fertilizer mixer. For cost purposes, from the pull box to the 400A disconnect, I plan to pull 750MCM XHHW ALUMINUM......BUT I cant get that in a 3" conduit....

Therefore, I want to pull 500MCM copper through 3" into the transformer, and splice to the 750MCM aluminum running to the fertilizer mixer......will this work?

One local inspector says it will be ok. He has no issue.....BUT he is in a different jurisdiction than where the job is.....so.......:whistling2:

Thoughts? Ideas?