NEC Fundamentals, Definitions, and General Wiring Requirements
What this domain tests
NEC fundamentals are the grammar for every low-voltage installation. Expect definitions from Article 100, the chapter structure (Chapters 1-4 general, 5-7 special, 8 communications, 9 tables), and general wiring rules for conductors, boxes, ampacity, and overcurrent protection. Low-voltage work still uses listed materials and approved methods.
Core rules
- Article 100 definitions control: listed, labeled, approved, accessible, and readily accessible have specific meanings.
- Chapter 3 wiring methods apply unless a special article permits otherwise. Boxes must be sized per Article 314; conductors must be protected from abrasion and strain.
- Ampacity comes from Article 310 tables, then is limited by termination temperature and 240.4(D) small-conductor rules.
- Overcurrent protection is selected to protect the conductor and equipment, not just the load.
Worked example
A 20 A branch circuit uses 12 AWG copper THHN. Table 310.16 shows 25 A at 75 degrees C, but 240.4(D) limits 12 AWG copper to a 20 A overcurrent device for general wiring. If the terminals are rated 60 degrees C, the ampacity is 20 A. The correct breaker is 20 A, and the 75 degrees C column cannot be used to justify a 25 A breaker.
Traps
- Using the 90 degrees C ampacity for terminations rated 75 degrees C.
- Ignoring the small-conductor overcurrent limits.
- Overfilling boxes or using unlisted fittings.
- Assuming low voltage means no Article 100 definitions or Chapter 3 methods apply.