Guess I was confused on definition of "Separately derived system" and "Non-separately derived system". The generator manufacturer sent me a illustration from Mike Holt here, and says that when the neutral is Not switched, it is a "Non-separately derived system" and the neutral and ground have to be separated, and when the neutral IS switched in a transfer switch, it is a "Separately derived system" and does not have to be separated. So when using a "generator inter-lock" bracket, as I'm planning on doing, it is considered a "Non-separately derived system". Sort of confusing, but still looks like in my application, they still need to be separated. Do all agree? Thanks