National Electrical Code
Structure and method
The NEC is organized into Chapters 1-4 (general), 5 (special occupancies), 6 (special equipment), 7 (special conditions), 8 (communications), and 9 (tables). Chapters 1-4 apply generally; later chapters modify or supplement them. Questions often test whether you know which article governs and which section is the general rule versus the exception.
Concepts you must own
- Wiring methods and support: cable and raceway support intervals, securing within 12 in. of boxes, and protection from physical damage.
- Boxes and fill: conductor fill, box fill calculations, and device box sizing.
- Grounding and bonding: system grounding vs. equipment grounding vs. bonding; the grounding electrode system and its connections.
- Overcurrent protection: conductor ampacity, derating for temperature and conduit fill, and the next-size-up rule.
- GFCI and AFCI: where required, and how requirements differ by location and occupancy.
- Receptacles and switches: spacing, ratings, and outlet requirements.
Traps
Assuming a local amendment matches the model code; assuming a special-occupancy article overrides a general rule when it only supplements it; confusing bonding with grounding; and forgetting that ampacity adjustments apply before selecting overcurrent protection.
Worked example
A conductor's adjusted ampacity lands at 68 A. Standard breaker sizes step 60 A to 70 A. The next-size-up rule permits rounding up to the next standard rating only when the ampacity does not correspond to a standard size and the load does not exceed the rounded-down device rating, and only where the code permits it. Verify the load first; do not round up blindly.