Equipment for General Use (NEC Articles 400-460)
Articles 400 through 460: equipment for general use
Article 400 restricts flexible cords: they may not substitute for the fixed wiring of a structure, may not run through holes in walls, ceilings, or floors, and may not be attached to building surfaces (400.12). Article 406 covers receptacles, including replacement rules (406.4) and tamper-resistant requirements. Article 408 governs panelboards: 408.36 requires each panelboard to be protected at not more than its rating, and a back-fed main needs a field-installed hold-down. Article 410 covers luminaires, including closet clearances (410.16).
Article 422 applies to appliances: disconnecting means, cord-and-plug connections, and overcurrent protection per the nameplate. Article 424 covers fixed electric space heating: branch circuits are sized at 125 percent of the load because heaters are continuous, with a disconnect for each unit and for the thermostat where required. Article 450 covers transformers, with 450.3 setting the OCPD at 125 percent of primary current for transformers with primary-only protection (next standard size up allowed for primaries 9 A and above).
Worked example: a 45 kVA, 480 V three-phase to 208/120 V transformer. Primary current = 45,000 ÷ (480 × 1.732) = 54.1 A; 125 percent = 67.7 A, so the next standard size is a 70 A primary breaker.
Traps: using flexible cord as permanent wiring, forgetting the 125 percent factor for heaters and water heaters, and confusing transformer primary-protection percentages with secondary-protection percentages.