Services, Feeders, and Branch Circuit Calculations
Load calculations (Article 220)
The standard method starts with general lighting at VA per square foot by occupancy (3 VA/ft² for dwellings), 1500 VA per small-appliance branch circuit, and 1500 VA for laundry. Apply Table 220.42 demand factors to the total: the first 3000 VA at 100%, the remainder at 35% for dwellings. Ranges use Table 220.55, electric dryers use 220.54 with a 5000 VA minimum, and four or more fixed appliances may use the 75% allowance in 220.53. The optional method (220.82) allows 100% of the first 10 kVA plus 40% of the remainder.
Branch circuits, feeders, and services
210.11(C) requires the 20 A small-appliance, laundry, and bathroom circuits. 210.52 sets receptacle spacing: no point along the wall line may be more than 6 ft from a receptacle, which works out to receptacles no more than 12 ft apart; kitchen countertops need receptacles within 24 in of the ends and no more than 48 in apart. 210.8 (GFCI) and 210.12 (AFCI) locations are frequent questions. Feeders follow Article 215; services follow Article 230. 230.42 sizes service conductors at 125% of continuous plus 100% of noncontinuous load, 230.90 sets service overcurrent protection, and 230.70 requires a disconnect at a readily accessible point nearest the entry of the conductors.
Trap: apply demand factors in the order the table lists them, and do not apply a dwelling demand factor to a non-dwelling occupancy.
Worked example: 2000 ft² dwelling - 6000 VA lighting + 3000 VA small appliance + 1500 VA laundry = 10,500 VA. Demand: 3000 + 7500 × 0.35 = 5625 VA, or 23.4 A at 240 V, before adding range, dryer, water heater, and HVAC.