Wiring Methods, Raceways, and Enclosures
What you must understand
Know the recognized wiring methods and where each is permitted or prohibited: rigid metal conduit, intermediate metal conduit, electrical metallic tubing, PVC, liquidtight flexible conduit, armored cable, metal-clad cable, nonmetallic-sheathed cable, and open wiring. Understand conduit fill (the 40 percent rule for three or more conductors), raceway support spacing, bend radius, and the number of bends between pull points (no more than 360 degrees total). Enclosure types and their environmental ratings (NEMA 1, 3R, 4, 12) matter, and Alaska conditions make wet-location and corrosion ratings especially relevant. Know box fill calculations and the volume allowances per conductor, device, and fitting.
Traps
Questions frequently test support distances: EMT every 10 feet, rigid every 10 feet, and within 3 feet of a box or fitting. Another trap is confusing the 360-degree total bend limit with the individual bend radius requirement. Box fill questions often omit the clamp, the device yoke, or the ground wire allowances. In damp and wet locations, remember that nonmetallic-sheathed cable is generally not permitted.
Rule of thumb and worked example
A quick fill check: for three or more conductors, conductors may occupy no more than 40 percent of the raceway interior cross-sectional area. Example: a box with four 12 AWG conductors (2.25 cubic inches each = 9.0), one cable clamp (2.25), and one device (4.5) totals 15.75 cubic inches, so a 4 × 4 × 1.5-inch box rated at 21 cubic inches is adequate. Always list every component before adding.