General Code Requirements, Definitions, and Administration
Reading the Code
Articles 90 and 100 set the ground rules. Article 90 states the NEC is not a design manual (90.1), explains the arrangement of the chapters (90.3: Chapters 5, 6 and 7 supplement or modify Chapters 1 through 4), and defines mandatory ('shall') versus permissive ('may') language (90.5). Article 100 definitions decide many exam questions. 'Listed' means evaluated by a recognized testing laboratory; 'labeled' means the label is on the product; 'approved' means acceptable to the authority having jurisdiction (AHJ). A listed product is not automatically approved, and approval may be refused.
Article 110 covers installation requirements: 110.3(B) requires equipment to be installed per its listing and instructions; 110.12 requires neat, workmanlike work; 110.14 requires proper terminations tightened to the torque marked on the equipment; 110.26 requires working space, dedicated equipment space, and an access 30 in. wide by 6 ft 6 in. high.
Worked example: a 480Y/277 V panelboard faces a concrete wall. Because the voltage exceeds 150 V, Table 110.26(A)(1) applies: Condition 1 (nothing opposite) is 3 ft; Condition 2 (grounded surface opposite, such as the concrete wall) is 3 1/2 ft; Condition 3 (live parts opposite) is 4 ft. Selecting 3 ft because 'the wall isn't metal' is the classic wrong answer - concrete counts as a grounded surface.
Traps: confusing working-space depth with the 6 ft 6 in. height or 30 in. width; treating 90.4 (AHJ enforcement) as a license to ignore rules; treating informational notes as enforceable code text.