John,
Figure a MDP with a trough above it. All of the branch circuits run through this trough. All the branch and feeder circuits have proper OC protection. Then you take this 400 amp wire and run it through the same trough. The 400 amp wire feeds a fused disconnect which then goes to a sub panel. This has a 400 amp breaker being back fed from a large PV system on the roof.
Where the 400 amp. feeder originates is at some lugs on the bottom of the MDP cabinet. I didn't see if the lugs are attached to because the cover was on and the EC didn't have tools to take it off. I also didn't have any extra paperwork with me it was in the office at the time. I don't know if an engineer signed off about the amperage of the bus bar. I will check today.
