Article 210 provides the requirements for branch circuits. As with most NEC Articles, it has its own general requirements. Like the arrangement in many Articles, those consist of Part I. Section 210.6 provides the voltage limitations of branch circuits.

• In dwelling units, motel guest rooms, and similar occupancies, the nominal voltage cannot exceed 120VAC between conductors [Sec. 210.6(A)].
• Branch circuits not exceeding 120VAC between conductors can be used in the three applications listed in Sec. 210.6(B). For example, cord and plug-connected equipment.
• Branch circuits exceeding 120VAC but not 277VAC can supply cord and plug-connected equipment or permanently connected utilization equipment or any of the eight types of luminaires listed in Secs. 210.6(C)(1) through (8).
• Branch circuits exceeding 277VAC but not exceeding 1000VAC can supply any of the loads listed in Secs. 210.6(D)(1) through (3). For example, permanently connected utilization equipment other than luminaires.

Ground fault protection for personnel is a general requirement for branch circuits. It’s required in the dwelling unit locations listed in Secs. 210.8(A)(1) through (14). For example, kitchens. It’s also required in the non-dwelling unit locations listed in Secs. 210.8(B)(1) through (16). For example, kitchens (again, yes). And in places such as rooftops and laundry areas. Other required locations are in Secs. 210.8(C) through (F). For example, sump pumps and vending machines.

You can’t derive a branch circuit from an autotransformer unless that branch circuit has a grounded conductor (neutral) that is electrically connected to a grounded conductor of the circuit supplying the autotransformer [Sec. 210.9]. This is because an autotransformer has a single coil serving as both the primary and secondary, thus the primary and secondary are not electrically isolated from each other.

How many branch circuits are required, and do the loads need to be evenly proportioned among them? The answers are in Sec. 210.11. The requirements for arc-fault circuit-interrupter protection are in Sec. 210.12. You must provide AFCI protection by one of the means listed in Secs. 210.12(A)(1) through (6). For example, a listed AFCI breaker. Which circuits must be AFCI-protected depends upon the type of occupancy: dwelling units, dormitories, or other occupancies [Secs. 210.12(B), (C), and (D)].

The requirements for GFCI protection of equipment are in Sec. 210.13. These are different from those for personnel [Sec. 210.8] and so are the devices and current thresholds for each.