General Requirements and Administration
Scope and Structure
The NEC is organized so that general rules come first and specific rules modify them later. A candidate must understand Article 90 (scope and purpose) and Article 100 (definitions), because many questions turn on precise wording rather than intuition. Know the difference between "shall" (mandatory), "shall not" (prohibited), "should" (recommended, in informational notes), and "may" (permissive). Informational Notes are explanatory only and are not enforceable.
Enforcement and Approval
Article 90 makes clear that the authority having jurisdiction (AHJ) interprets and enforces the code. Approval of equipment and materials is the AHJ's call; listing by a qualified testing laboratory is strong evidence but not a substitute for AHJ approval. Understand examination, identification, and use of listed equipment, and the requirement that equipment be installed per its listing and labeling instructions.
Traps
- Confusing Informational Notes with mandatory text.
- Assuming a listing guarantees acceptance; the AHJ still approves.
- Missing that Chapter 5, 6, and 7 rules can supplement or modify Chapters 1-4, and that specific rules govern over general ones.
- Forgetting that metric and inch-pound units are both given, and that code text governs over tables in conflict.
Worked Example
A question asks whether unlisted equipment may be installed. Rule of thumb: unlisted equipment may be acceptable only where the AHJ permits it and it is found suitable for the purpose; listing is the normal path but not the only legal one. Read the exact wording of the article before choosing.
Rule of Thumb
When two rules conflict, the more specific article governs, and mandatory text beats informational notes every time.