Which NEC article covers wiring methods and conductors such as NM-B and THHN?

• A. Article 310 (and related Articles 300 for wiring methods)
• B. Article 210
• C. Article 230
• D. Article 400

Answer: (A)

The essential idea is where the NEC places rules for the parts you’re using. NM-B and THHN are both types of conductors used in electrical installations. The article that governs conductors sets the standards for what kinds of conductors can be used, their insulation, temperature ratings, ampacity, and general use. THHN is a common single-conductor type used in conduit, and NM-B is a type of nonmetallic-sheathed cable; both fall under those conductor rules (with NM-B having its own cable-specific definitions in the code). Wiring methods, which describe how those conductors are installed, routed, protected, and connected, are handled in a separate article focused on wiring methods.

The other topics addressed by the other articles relate to different parts of the system (like branch circuits, services, or flexible cords) and don’t cover the general conductor types you mentioned.