Generator ratings specify the _________ and ___________ at which they can operate safely.

The correct answer focuses on "voltage" and "frequency," which are critical parameters in determining how generators operate within the electrical grid. Generator ratings are typically provided by manufacturers to ensure that the equipment can function safely and efficiently under specific operational conditions.

Voltage refers to the electric potential provided by the generator, which must match the system voltage for proper integration into the grid. If a generator operates outside its rated voltage, it could lead to equipment damage, decreased efficiency, or even circuit failure.

Frequency is also vital, particularly in alternating current (AC) systems, because it dictates the timing of the voltage cycles. In many regions, the standard frequency is either 50 Hz or 60 Hz. Operating at incorrect frequencies can cause various issues, including instability in the power system and operational inefficiencies.

While other options mention various attributes related to generators, they do not directly address the critical operational parameters essential for safety and efficiency in generating electricity. Therefore, highlighting voltage and frequency captures the essence of operational ratings for generators in the NERC context.