Branch Circuits, Feeders, and Service Calculations
Branch Circuits, Feeders, and Service Calculations
This domain tests Article 220 load calculations and Article 210 branch-circuit rules: receptacle spacing, small-appliance and laundry circuits, lighting VA, demand factors, and service sizing.
Core rules
- Dwelling general lighting: 3 VA/ft²; small-appliance: two 1,500 VA circuits; laundry: 1,500 VA.
- Demand factor for dwelling lighting and receptacle loads: first 3,000 VA at 100%, remainder at 35% (220.42).
- Kitchen counter receptacles: no point along the wall more than 24 in from a receptacle; island and peninsula rules apply.
- Bathroom receptacles require 20 A GFCI branch circuits; laundry requires a 20 A circuit.
- Service and feeder conductors are sized from calculated load, then protected by OCPD.
Worked example
A 2,000 ft² dwelling: general lighting = 2,000 × 3 = 6,000 VA. Small appliance = 2 × 1,500 = 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; demand load = 5,625 VA. Add fixed appliances, range, dryer, and HVAC at their Code demand values before sizing the service.
Traps
- Applying the 35% demand factor incorrectly to small-appliance or laundry circuits.
- Forgetting the two small-appliance circuits.
- Measuring receptacle spacing around corners incorrectly.
- Sizing service conductors from connected load without demand factors.