Wiring and Protection
Branch circuits and feeders
Article 210 sets branch-circuit ratings, conductor minimums, receptacle spacing, and GFCI/AFCI requirements. In dwelling units, 210.8 requires GFCI protection for bathroom, kitchen, laundry, garage, outdoor, basement, and unfinished-area receptacles, and 210.12 requires AFCI protection for essentially all 120 V, 15 A and 20 A branch circuits. Kitchen counter receptacles must be spaced so no point is more than 24 in. from a receptacle; general wall spacing is the 6 ft/12 ft rule. Dwelling units need two 20 A small-appliance circuits, a laundry circuit, and a bathroom circuit. Article 220 governs load calculations; Article 240 governs overcurrent devices.
Overcurrent protection
240.4 protects conductors against overcurrent; 240.4(D) limits 14, 12, and 10 AWG. The next-size-up rule (240.4(B)) allows rounding up to the next standard rating only where the ampacity does not correspond to a standard size, the device is 800 A or less, and the load does not exceed the conductor ampacity. Tap conductors are permitted only under 240.21(B) with specific length and ampacity conditions. Service equipment must be grouped, have a disconnect at a readily accessible location nearest the point of entry (230.70), and have a grounding electrode conductor installed per Article 250.
Traps
Confusing AFCI with GFCI, applying the next-size-up rule to small conductors, forgetting the 125% multiplier for continuous loads, and assuming a service disconnect may be at any convenient indoor location.
Worked example
A 65 A continuous load needs conductors rated at least 81 A (65 × 1.25); 4 AWG copper at 75 °C (85 A) works with an 80 A or 90 A device, whichever the load permits.