Older commercial building with 400 amp single phase service. The power company lines come into the building and go directly to a fused 400 amp disconnect. From there they split to a 200 amp fused disconnect and two 100 amp disconnects.
At the end of each of those 3 disconnects are modern day 200 amp panel and two 100 amp panels. Are those modern day panels main panels or subpanels? Do I isolate the ground and neutral bars or leave them connected on these modern day panels?