Our job includes installing an 2 outdoor 250 kW 3 phase 4 wire 480 Volt enclosed generators. One site has a 600 Amp 3 phase 4 wire main breaker supplying the normal side of a 600 Amp 3 Pole Automatic Transfer. The main breaker and ATS are in the same room. The generator has a 600 Amp breaker mounted on the generator (capable of being locked open)inside the generator enclosure. The generator is about 100' from the building. The neutral in the generator is isolated from the frame. We are running 4 wires + gnd. into the building. My question is does the since I believe the NEC does not consider this a separately derived service (3 pole ATS) are the generator feeder cables considered a service entrance and thus require to have a disconnecting means where the cables enter the main building. The system neutral and the generator neutral are connected together on an isolated bus section in the ATS.
The other site is similar except the is a 4 pole transfer switch. Since this is considered a separately derived service does this installation require a disconnect switch inside the main building on the generator cables before they terminate in the ATS.
The generator conductors are, as you stated, feeder conductors and therefore no "service" disconnect would be required. It is, however, my opinion that Article 225 will require you to provide a disconnect for the generator conductors at the building. Don(resqcapt19)
