we are building a new steel facility with a 400A 208 3-ph service It cconsists of (1) CT cabinet and (2)200 Main Bkr Panels. The service entrance conductors from the parallel lugs of CT cabinet are (2) sets of 3/0 AWG, with full neutrals. I understand 250.66 typically requires at least a #1/0 for the GEC on a 400A service, and that when parallel feeders are used, the sum of their equivalent areas is used. However, since we have two 200 A main bkr panels, are these still considered parallel feeders. Am I correct to say that a #4 from each panel N to bldg. steel would suffice? NOTE: Assuming Bldg.steel is sufficiently bonded to water pipes, and a supplemental driven ground is used outside at CT Cabinet.