Branch Circuits, Feeders, and Boxes/Raceway Fill
Branch circuits and feeders
Article 210 covers branch-circuit ratings, receptacle spacing, and required outlet circuits. Kitchen small-appliance circuits, laundry circuits, bathroom circuits, and garage circuits have special rules. GFCI protection is required in bathrooms, garages, outdoors, kitchens, and other specified areas. AFCI protection is required for many dwelling-unit branch circuits. Article 215 covers feeders, including minimum ampacity and overcurrent protection. Boxes and raceways are covered by Article 314 and Chapter 9.
Box fill and raceway fill traps
Box fill under 314.16 is a common calculation question. Count each circuit conductor, count all equipment grounding conductors as one allowance based on the largest, count internal cable clamps as one, and count a device yoke as two conductor allowances. Do not count a plaster ring unless the box volume marking includes it. For raceways, use the Chapter 9 fill tables and do not exceed the permitted percentage. Pull boxes with large conductors have separate dimension rules under 314.28.
Worked example
A box contains two 12 AWG cables, each with hot, neutral, and ground. It has one internal clamp and one device. Count four circuit conductors, one equipment grounding allowance, one clamp allowance, and two device allowances: eight allowances. At 2.25 cu in. per 12 AWG conductor, the required volume is 18 cu in. A box marked 18 cu in. or larger is acceptable. Rule of thumb: count EGCs once, clamps once, and a yoke as two.