400a 480y wire and conduit sizing

[Moosifer]

Customer keeps wanting bigger stuff out of my comfort zone.
They want to add a 480Y/277 3Ø 4W Wye panel to the main panel for a building if the supply transformer is big enough.
It is about 170ft run. I want to plan for potential 400a load and I was thinking Al 300 XXHW parallel in 2qty 3" rigid conduits with #3 Cu ground in each?
Does that sound appropriate? Any thing I need to know that isn't obvious like spacing between conduits, etc?

 

[Dennis Alwon]

You could avoid the #3 copper as rigid is suitable as an equipment grounding conductor. Section 344.60

 

[infinity]

I would bump the RMC up to 3½" and run all of the 300's in a single raceway.

 

[augie47]

If you want to avoid a 3" conduit, run (2) 2" with 250 kcmil XHHW-2 Compact.

 

[don_resqcapt19]

Is there an overcurrent protective device at the transformer or are these transformer secondary conductors.?

 

[Moosifer]

Is there an overcurrent protective device at the transformer or are these transformer secondary conductors.?

There is a panel at the transformer.

 

[infinity]

There is a panel at the transformer.

Then you have many options with running the 400 amp feeder. As Augie suggested you could use smaller conductors. With 2 sets of parallel 250's you would still only have a VD of a little over 1% at the full 400 amps.

 

[electrofelon]

There is a panel at the transformer.

What are the conditions of this wire run? Is it underground, exposed, covered, surface mounted?