Branch Circuits, Feeders, and Services
Branch Circuits, Feeders, and Services covers Articles 210, 215, 220, and 230: receptacle and lighting requirements, branch-circuit ratings, dwelling load calculations, feeder and service conductor sizing, and minimum service ratings. The exam favors standard-method dwelling calculations and the 6 ft/12 ft receptacle rule.
Branch-circuit rules
- Dwelling receptacle spacing (210.52): no point on a wall space more than 6 ft from a receptacle, so receptacles are generally at most 12 ft apart.
- Small-appliance branch circuits: two or more 20 A circuits in a dwelling kitchen; laundry also requires a 20 A circuit.
- Bathroom receptacles require a 20 A branch circuit and GFCI protection (210.8).
- AFCI protection is required for most dwelling branch circuits under 210.12.
- Continuous loads: branch-circuit and feeder conductors and OCPDs are sized at 125% of continuous load plus 100% of noncontinuous load (210.19, 215.2).
Standard dwelling calculation (220.42, 220.52)
General lighting = 3 VA/ft². Small-appliance circuits = 1,500 VA each; laundry = 1,500 VA. Apply the demand factor: first 3,000 VA at 100%, the remainder at 35%.
Worked example
A 2,000 ft² dwelling: general lighting = 3 × 2,000 = 6,000 VA; two small-appliance circuits = 3,000 VA; laundry = 1,500 VA. Total = 10,500 VA. First 3,000 at 100% = 3,000; remaining 7,500 at 35% = 2,625. Demand load = 5,625 VA before appliance, range, dryer, and motor additions. At 240 V that is 23.4 A, so a 100 A service is the Code minimum (230.79).
Traps
- Applying 35% to the entire load instead of only the amount above 3,000 VA.
- Forgetting the laundry circuit or counting only one small-appliance circuit.
- Using 3 VA/ft² for garages or unfinished basements that have separate rules.
- Omitting the 25% addition for the largest motor.
- Using 310.12 dwelling service conductor allowances for a feeder that is not a dwelling service.