Wiring Methods, Materials, and Installation Practices
Core concepts
Know the common Chapter 3 wiring methods-NM cable, AC/MC, EMT, IMC, rigid metal and PVC conduit, LFMC, and raceway systems-and where each is permitted or prohibited. Understand conductor types and insulation (THHN, THWN, XHHW), ampacity tables, conduit fill (Chapter 9, Tables 1 and 4), and support and securing requirements. Boxes must be accessible, sized for fill, and supported. Know bending radii, expansion fittings, and the difference between grounding and bonding. Recognize the requirements for wet, damp, and dry locations, and for plenum and hazardous locations.
Traps
Questions test whether a wiring method is permitted in a given location (e.g., NM cable in a commercial ceiling, EMT in a corrosive area). Conduit fill uses total conductor area versus conduit internal area, and the 40% fill rule for three or more conductors. Remember that conduit bodies with splices must be sized per 314.16. Support distances vary by method-memorize common ones.
Worked example
Sizing conduit: for four 12 AWG THHN conductors, look up each conductor's area in Chapter 9 Table 5, sum them, then select the smallest conduit whose 40% area (Table 4) exceeds the total. This is a lookup exercise-precision matters.
Rule of thumb
If a wiring method question mentions a location type (wet, plenum, hazardous), the answer is usually about permitted use, not ampacity.