Branch Circuits, Feeders, and Service Load Calculations
Circuits, feeders, services
Article 210: 210.8(A) requires GFCI protection for essentially all 125-250 V receptacles in dwelling kitchens, bathrooms, laundry areas, garages, basements, outdoors, and near sinks; 210.8(B) extends coverage to non-dwelling kitchens, bathrooms, rooftops, and outdoor outlets. 210.12 requires arc-fault protection for dwelling-unit branch circuits. 210.11(C) requires 20 A small-appliance, laundry, and bathroom circuits. 210.52 sets receptacle spacing: the 6 ft/12 ft rule, 2 ft of wall space, 4 ft along countertops, and island/peninsula outlets.
Article 220 load calculation: standard method uses 220.42 lighting demand (first 3,000 VA at 100%, next 117,000 VA at 35%, remainder at 25%), 220.52 (1,500 VA each for small appliance and laundry), 220.55 (ranges), and 220.53 (75% demand for four or more appliances). The optional method, 220.82, takes the first 10 kVA at 100% and 40% of the remainder, then adds heating or cooling per 220.82(C). Feeders are sized at 125% of continuous plus 100% of noncontinuous load (215.2(A)(1)). Article 230 covers service conductors; 230.79(C) sets 100 A as the minimum service rating for a one-family dwelling.
Worked example: 1,800 ft2 dwelling, optional method: lighting 5,400 VA + small appliance 3,000 + laundry 1,500 = 9,900; add an 8,000 VA range = 17,900; first 10,000 at 100% plus 40% of 7,900 (3,160) = 13,160 VA; divided by 240 V = 55 A. The service is still 100 A because of 230.79(C).
Traps: using the optional method on a store; forgetting the 125% continuous-load factor; assuming the old six-throw rule still applies.