I will have a portable generator that will be on occasion connected as a separately derived source and at times not a separately derived source.
When I have a tool directly plugged into the generator mounted receptacle, it will be a separately derived system. When I have the generator recept connected to house wiring through a 2 pole transfer switch (neutral not switched), it will not be a separately derived source.
250.34(C) dictates that as a separately derived source, the grounded conductor must be bonded to the generator frame. As a non-separately derived source, it would not have its grounded conductor bonded to the frame.
Remember since all loads will be connected through the generator mounted receptacles, no connection of the frame to a grounding electrode system is required 250.34(C).
OK, now the theory question. How does the functionality and safety characteristics change if the neutral to frame remains connected or unconnected (only one way or the other) when the gen is used as a non-separately derived source and a separately derived source. I cannot grasp why it is necessary to change the generator from bonded to unbonded if I plug the tool into the gen directly or into a recept in my home (which is plugged into the gen through the xfer switch).