Roger- 250.30 only applies to seperately derived systems, like if you used a 4-pole switch to switch the neutral at a generator ATS which was bonded both at the generator and the service entry. If he bonded at both the transformer and panel but replaced the neutral wire between them with a ceramic insulator, the neutral current would simply flow between the ground points, and the problem would still exist.
Steven, I'd wager that Redsy is talking about an SDS and a switched neutral has nothing to do with it. If you bond at both locations and there is a parallel path as in metallic raceways you will have net currents flowing in the common GES resulting in EMF issues.
Roger
