Using the tap rule for Sub-panel

[jbl]

I hope this is not too confusing.
I am needing to come out of a 400A amp panel to feed a sub-panel that will be protected at 175A. This sub-panle will be used for a Solar backfeed. Since the panel is rated at 400A, after applying the 120% rule for loading the bus, 705.12(D)(2) I am limited to a combine feed of 480A on the bus. I had a load calculation done and found it feasible to reduce the size of the Utility main breaker to 300A. This would allow up to 180A backfeed from the Solar arrray. This is where the 175A sub-panle comes in. I am needing to feed it out of the 400A panel but do not have breaker space to accommodate the 175A breaker needed to feed the sub-panel. I am wondering id I can "tap" the 400A bus with 2/0 Copper and run directly outside to a 200A fusible disconnect, fused at 175A (this disconnect would act as utility disconnect for Solar array) then back inside to a sub-panel that will house all Inverter backfeeds. The total length is less than 25ft. Can I use the tap rule as protection for these conductors and panel? Do I also need a disconnect or breaker inside that is within site of these panels?
Note: The sub-panel will be mounted next to existing 400A panel, ~5ft apart.
Breakers space in sub-panel will be limited ONLY to PV Inverter feeds, no additional loads.

 

[Dennis Alwon]

There are tap rule in art. 240 but it is hard to tell if they apply.

 

[macmikeman]

Make sure to keep the conductors in a raceway. I keep running across PV tap jobs done with ser cable or romex cable, some exposed and some run inside the framing space from an exterior meter/main to an adjacent framing bay behind exterior sheathing, to a pv disconnect. That may make it easier to route , but is a code violation.

 

[jbl]

Is Ser cable legal inside a structure if it is on the A/C side of a PV sub-panel? (a different project than previous mentioned)
This would be running from PV sub-panel which is mounted outside adjacent to array, then ran through house, back out into utility PV disconnect, then a line side tap.

 

[jbl]

Just a side note:
The purpose for all of the required "engineering" on this project is that the local utility does not allow "line side" taps for PV that are permissible by NEC. This would make this project much easier to design.