Wiring Methods and Materials: Cables, Raceways, Boxes, and Fittings
Domain 2 tests whether you can choose a wiring method that is legal for the location and install it with the right support, protection, and box capacity. Most lost marks here come from a single detail: the temperature or location limit attached to a cable.
Cable wiring methods
NM-B (Article 334) has 90°C conductors, but 334.80 limits ampacity to the 60°C column, so 12 AWG NM is a 20 A conductor. NM is for dry locations and must be supported every 4.5 ft and within 12 in of each box (334.30), with physical protection where 334.15(B) requires it. Where cable passes through bored holes, 300.4 keeps it at least 1¼ in from the framing face or behind a nail plate. UF (Article 340) is the underground and damp-location cable, buried at Table 300.5 depths. AC and MC cables use their own articles and bonded armor.
Raceways
EMT (358.30) is supported every 10 ft and within 3 ft of a box; PVC (352.30) every 3 ft with expansion provisions for temperature change. Conduit fill comes from Chapter 9, Table 1: 53% for one conductor, 31% for two, 40% for three or more. Bends must respect the radius in Chapter 9, Table 2, and 314.28 sizes pull boxes by the raceway trade size and the number of conductors.
Boxes and fill
314.16(A) gives box volume; 314.16(B) gives per-conductor allowances: 14 AWG = 2.0 cu in, 12 AWG = 2.25, 10 AWG = 2.5. Each cable clamp counts as one of the largest conductor, all equipment grounding conductors together count as one, and each yoke or device counts as two of the largest conductor.
Worked example
A 4 × 4 × 1½ in square box has 22.5 cu in. It contains two 12/2 NM cables and one receptacle: four circuit conductors (4 × 2.25 = 9.0), one ground allowance (2.25), one clamp allowance (2.25), and the device (2 × 2.25 = 4.5). Total 18.0 cu in against 22.5 available - compliant with 4.5 cu in to spare.
Traps
Using 90°C ampacity for NM; ignoring the clamp and device allowances in box fill; supporting cable 18 in from a box; installing NM in a damp crawl space; forgetting nail plates on shallow-notched studs.