Wiring Methods, Materials, and Installation Practices
This domain tests whether you can select a wiring method for the location and install it legally: cable and conduit types, support and protection, box fill, conduit fill, bending, and termination. Questions often combine a product standard with an installation rule.
Methods and permitted uses
- NM-B (Article 334): dry locations, concealed or exposed in permitted areas; not wet or damp locations, not embedded in masonry, not in hazardous locations.
- AC (320) and MC (330): armored and metal-clad cable, with specific grounding and support rules.
- EMT (358), PVC (352), FMC (348), LFMC (350), ENT (362): each has permitted uses, support intervals, and bending rules.
- 300.4 requires protection where conductors are within 1¼ in. of framing edges; 300.15 requires a box or fitting at each splice, angle, or termination.
- 314.16 governs box fill; Chapter 9 governs conduit fill and bending radius.
Worked example
A 4 × 4 × 1½ in. box has 21.0 in³. Each 12 AWG conductor counts 2.25 in³. Three circuit conductors = 6.75 in³; one equipment grounding conductor = 2.25 in³; one cable clamp = 2.25 in³; one device yoke = 2.25 in³. Total = 13.5 in³, so the box is adequate. All equipment grounding conductors together count as one conductor volume based on the largest. Add a second cable with two more circuit conductors and the total becomes 18.0 in³, still within 21.0 in³.
Traps that cost marks
- Counting each grounding conductor separately instead of as one volume.
- Forgetting the clamp or device yoke.
- Choosing a box by dimensions without checking Table 314.16(A) volume.
- Exceeding the 40% conduit fill limit for three or more conductors.
- Using NM cable outdoors or in wet locations.
- Supporting EMT or PVC at the wrong interval, or omitting expansion fittings on PVC.
- Ignoring the minimum bending radius for the raceway and conductor type.