- N minus 1 – is the system condition when one major component is unavailable. A major component can be a transmission line or a critical transformer. The letter N meaning the normal system configuration where all components are in service.
- N minus 2 – is the system condition when a second major system component becomes unavailable This system condition causes heightened concern that the still operational parts of the grid might not be sufficient to supply the load resulting in possible brownouts or blackouts.
- N minus 3 – is the system condition when a third major component is unavailable. At this point the entire transmission grid can become unstable requiring emergency measures be taken to prevent further equipment damage and the collapse of the entire grid.
- If the terrorist [click attack] disables three or more major components quickly the entire transmission grid supplying power to the target city will automatically be taken off line by the protective relays blacking out the target city.