Branch Circuits, Feeders, and Service Calculations
Branch Circuits, Feeders, and Service Calculations
This domain tests Article 210 branch-circuit rules, Article 220 load calculations, and Article 215 feeder sizing. Expect dwelling and commercial load calcs, receptacle spacing, GFCI/AFCI requirements, and continuous-load factors.
Core rules
- General lighting load for dwellings is 3 VA per square foot (220.12). Small-appliance circuits: two or more 20 A circuits at 1,500 VA each; laundry: 1,500 VA.
- Demand factors under 220.42: first 3,000 VA at 100%; remaining general load at 35% for dwellings.
- Continuous loads are calculated at 125% for branch-circuit and feeder sizing (210.19, 215.2).
- Receptacle spacing in dwellings: no point along the wall is more than 6 ft from a receptacle (210.52). Bathrooms, kitchens, garages, and exteriors have specific GFCI rules.
- Standard overcurrent ratings are in 240.6; the next standard size is not always permitted.
Worked example
A 2,000 sq ft dwelling: general lighting = 2,000 × 3 = 6,000 VA. Two small-appliance circuits = 3,000 VA; laundry = 1,500 VA. Total = 10,500 VA. Apply 220.42: first 3,000 at 100% = 3,000; remaining 7,500 at 35% = 2,625; total demand = 5,625 VA. At 240 V, that is 23.4 A before adding range, dryer, or heating loads.
Traps
- Applying 100% to all general lighting load.
- Forgetting the small-appliance and laundry circuits.
- Sizing a feeder for a continuous load at 100%.
- Confusing receptacle spacing with other room requirements.