Article 700 is the first in a series of NEC Articles about on-site power systems, including 700, 701, 702, 705, and 708. Each covers a different kind of system, differentiated by mission. The systems/missions include legally required systems, optional standby systems, and backup systems. All of these (except backup systems) are defined in Articles 701 and 702. The definition of a backup system depends on what you’re backing up.
What about emergency systems? Such a system is ac