How long must backup functionality be sustained according to the periodic testing requirements?

The requirement for backup functionality to be sustained during periodic testing is set to two hours. This is a critical standard aimed at ensuring that backup systems can effectively respond to a failure or disruption in the primary systems they support. Sustainability for this duration allows for adequate assessment of the backup systems' capabilities, including their ability to maintain normal operational functionality without relying on primary systems.

The two-hour benchmark is designed to reflect real-world scenarios where prolonged disruptions might occur, and it also provides a thorough testing window to identify potential issues that could affect system reliability. This requirement is particularly essential for maintaining grid stability and ensuring that essential services remain operational, thus enhancing the overall resiliency of the system.