Wiring Methods, Materials, and Installation Practices
Methods and materials
Know the common wiring methods and where each is permitted: NM cable in dry interior locations, MC and AC cable with appropriate fittings, EMT, IMC, RMC, PVC, LFMC, and LFNC. Understand wet, damp, and dry location definitions, corrosion protection, and the difference between support and securing requirements.
Installation limits
Candidates must apply raceway fill percentages: 53% for one conductor, 31% for two, 40% for three or more. Box fill counts conductors, devices, grounds, and clamps using table values; a 4 × 4 × 1.5 inch box has 21 cubic inches. Bending radius, conductor derating for bundled conductors, expansion fittings, firestopping, and plenum ratings are frequent topics. Burial depth depends on raceway type and location.
Traps
Questions often swap support spacing, apply NM cable outdoors or in wet locations, or ignore that PVC requires expansion fittings. Box-fill questions may count a receptacle as two conductors and all equipment grounds as one. Do not assume a raceway is suitable for a wet location just because it is metal.
Worked example
A box contains four 12 AWG current-carrying conductors, two grounds, and one receptacle. Count 4 × 2.25 = 9.0 in³ for conductors, 2.25 in³ for the combined grounds, and 4.5 in³ for the device: 15.75 in³. A 4 × 4 × 1.5 box at 21 in³ is adequate. Rule of thumb: when in doubt, count every conductor entering the box and add the largest device allowance.