For 1200A @ 480/277V, service entrance with Bypass-isolation switch, Closed transition; I spoke to a vender and he recommended to use solid neutral type, my understanding for this application, since we have GFP for the breaker at the ATS, we need to use 4-Pole ATS (switched neutral) in lieu of 3-pole to avoid nuisance tripping. (The generator will be separately derive system). Any thoughts ? Thanks,