National Electrical Code (NEC) Requirements
Core concepts
The NEC is organized into Chapters 1–9, with Articles cited by number (e.g., 210 branch circuits, 250 grounding, 300 wiring methods, 310 conductors, 430 motors, 450 transformers). Candidates must know Article 100 definitions, the general requirements of Chapters 1–4, and how Chapters 5–7 modify or supplement them. Understand clearances, working space (Table 110.26(A)(1)), box fill (314.16), conductor ampacity and adjustment (310.15), overcurrent protection (240), grounding and bonding (250), and GFCI/AFCI requirements (210.8, 210.12). Know that the Code is minimum requirements and that local amendments may be stricter.
Traps
Questions love "shall" versus "should" and the difference between ampacity tables and termination temperature ratings (110.14(C)). Remember the small-conductor overcurrent rule (240.4(D)) and that the next-size-up rule (240.4(B)) has limits. Box fill counts conductors, devices, clamps, and grounds differently. Working-space depth is measured from the live parts, not the wall.
Worked example
A 12 AWG copper THHN conductor (75°C column, 25 A) on a 20 A breaker: verify termination rating. If the terminal is 60°C, use the 60°C column (20 A) and confirm the 20 A device is acceptable. Then apply any ambient or bundling adjustment factors from 310.15.
Rule of thumb
When a question cites an article number, the answer usually hinges on that article's specific exception or table-read for exceptions before calculating.