Conductor sizing from first disconnect to breaker panels

[Fred B]

If I up size conductors for voltage drop from POCO to first disconnect can the balance from first disconnect to branch circuit panels be sized to the amperage of the loads of the individual panels or must the upsized conductors carry thru to the branch circuit panels? For reason of VD running 2 parallel 500kcmil AL to 400A meter/disconnect can I run from the disco to the 2 interior breaker panels two sets of 250kcmil AL one set to each panel, under 25ft from meter/disconnect to the interior panels?

 

[infinity]

How long are the parallel 500's? Just eyeballing your numbers the 25' of 250 kcmil shouldn't change the VD very much. To know for sure you would need to calculate the enitre run with the two segments of different size conductors.

 

[Fred B]

How long are the parallel 500's? Just eyeballing your numbers the 25' of 250 kcmil shouldn't change the VD very much. To know for sure you would need to calculate the enitre run with the two segments of different size conductors.

Will have about 300ft total length POCO to breaker panels about 275ft from POCO to meter/disconnect.

 

[suemarkp]

I don't see any requirement to do this. VD is a choice, not code mandated. If you only do an upsize on the service conductors, I think the only conductor possibly affected would be the minimum size of the grounded conductor (there is no separate equipment ground yet to upsize). If you have phase to neutral loads, people rarely run a grounded conductor only sized to 250.66, so it will most likely be large enough.

I think the answer is the same for a feeder. If you upsize the ungrounded conductors of a feeder, you need to upsize the EGC in that feeder. You don't have to upsize any branch circuits. If you choose to do so, then any branch circuit upsized needs its EGC upsized.