Alternate ac source
Alternate ac source means an alternating current power source that is available to and located at or nearby a nuclear power plant and meets the following requirements:
(1) Is connectable to but not normally connected to the offsite or onsite emergency ac power systems;
(2) Has minimum potential for common mode failure with offsite power or the onsite emergency ac power sources;
(3) Is available in a timely manner after the onset of station blackout; and
(4) Has sufficient capacity and reliability for operation of all systems required for coping with station blackout and for the time required to bring and maintain the plant in safe shutdown (non-design basis accident).