I am not sure that 403 does apply. A little more color - we have (3) 400 AMP breakers that are the building disconnect (logically speaking, perhaps not a "building disconnect" as termed in the NEC, but you can flip these three switches and cut all building power.Service entrance equipment is usually treated differently then standard equipment, for example, UL has special requirements concerning barriers and bonding jumpers.
Pay attention to the NEC definitions for service locations and accessibility requirements or allowances. The secondary of a customer owned transformer is not a service entrance location although it has several similar requirements.
Why do you think 404.3 would apply to your situation?
Each of the 400 amps breakers feeds three separate PDUs, and each of the PDUs has a 125A OPCD (so the conductor from the 400A breaker lands at an OPCD, and we follow the tap rule). These PDUs are spread throughout the building. My understanding is that we need to stay within the six throws of the hand to disconnect the building power.