When must a generator be grounded as a separately derived system?

A generator must be grounded as a separately derived system when switching occurs in the grounded conductor to ensure safety and proper system operation. The grounding of a separately derived system is essential because it stabilizes the voltage during fault conditions and provides a reference point for the system's neutral. This helps to prevent potentially dangerous voltage differences that could occur if the system were left ungrounded.

In the case of switching activities, particularly when there are changes occurring in the system's grounding or in the conductors, grounding ensures that any transient voltages are safely dissipated and that any fault currents can be effectively managed. This also helps in protecting equipment and personnel from electrical hazards.

Other situations, such as continuous operation or merely being above a certain size, do not necessarily require grounding. Maintenance procedures can occur without the need for grounding unless there are specific switching actions that could impact system safety. Thus, the grounding requirement hinges significantly on the state of the conductor switching, making it crucial for safe and effective operation.