The NEC Articles That Carry Most of the Exam Questions
Twelve articles and a handful of tables account for most of the questions on journeyman and master exams. What each one covers, what gets asked, and the sections to know cold.
If you spread your study evenly across the code's 900 pages you will know a little about everything and not enough about the parts that are tested. Exam writers draw from the same articles year after year because those are the ones a working electrician uses. Here they are, with the sections that come up again and again.
Article 100, Definitions
Every exam opens with definitions, and they appear inside other questions too. Know the difference between accessible and readily accessible, between continuous load and the rest, between a feeder and a branch circuit, between a device and utilization equipment. Know bonding, grounded conductor, grounding conductor, and within sight. The definitions are short; read them twice.
Article 110, Requirements for Electrical Installations
110.3(B), equipment used according to its listing. 110.14, conductor termination temperature ratings, which decides which column of Table 310.16 you use. 110.26, working space: the depth, width and height numbers for equipment likely to need examination while energised, and the condition table that sets the depth. Master candidates add 110.24, available fault current labelling.
Article 210, Branch Circuits
The most-tested article on journeyman exams. 210.8, GFCI locations in dwellings and other occupancies. 210.11, the required circuits for small appliances, laundry and bathrooms. 210.12, AFCI. 210.19 and 210.20, the 125 percent sizing for continuous loads. 210.23, what a 15 or 20 ampere circuit may supply. 210.52, receptacle placement: the six-foot and twelve-foot wall rule, countertop spacing, island and peninsula receptacles, bathroom, garage and outdoor requirements.
Article 215 and 230, Feeders and Services
Feeder sizing follows the same 125 percent logic; 215.2 is the section. Services: 230.42 minimum size, 230.70 and 230.71 on disconnects, 230.79 the 100 ampere minimum for a dwelling, 230.24 clearances for overhead conductors. Master exams go deeper into service equipment, multiple services and where the service point is.
Article 220, Load Calculations
General lighting in VA per square foot, small-appliance and laundry loads, the demand factors in 220.42, ranges in Table 220.55, dryers in 220.54, the optional dwelling method in 220.82. Master exams add multi-family (220.84), commercial kitchens (220.56), and receptacle demand (220.44).
Article 240, Overcurrent Protection
240.4(B), the next-standard-size-up rule and the 800 ampere limit. 240.4(D), the small-conductor rule that caps 14, 12 and 10 AWG at 15, 20 and 30 amperes. 240.6, the list of standard sizes. 240.21, tap rules: the 10 foot, 25 foot and transformer secondary taps.
Article 250, Grounding and Bonding
250.24, grounding a service. 250.50 and 250.52, the grounding electrode system and which electrodes count. 250.53, electrode installation. 250.66 and its table, grounding electrode conductor sizing, with the exceptions for rod, concrete-encased and ring electrodes. 250.122 and its table, equipment grounding conductor sizing and the increase when conductors are upsized. 250.30 for separately derived systems, which master candidates must know.
Article 300 and 310, Wiring Methods and Conductors
300.4, protection against physical damage and the 1.25 inch setback. 300.5 and its table, burial depths. 300.15, boxes required. 310.15, ampacity with temperature correction and adjustment for more than three current-carrying conductors, including which conductors count. Table 310.16 itself, and 310.12 for dwelling service and feeder conductors.
Article 314, Boxes
314.16, box fill: the volume per conductor by size, how clamps, devices and grounding conductors count, and Table 314.16(A) for standard boxes. 314.23, supports. 314.28, pull and junction box sizing for conductors 4 AWG and larger: the six-times and eight-times rules.
The cable and raceway articles
334 nonmetallic-sheathed cable (where it is permitted, support intervals, the 60 degree ampacity rule). 344 rigid metal conduit, 352 PVC, 358 EMT: support spacing, bends, and where each is allowed. 348 and 350 flexible metal conduit. 342 IMC. Expect one question each.
Article 430, Motors
The single most-tested article in Chapter 4. 430.6, use the tables not the nameplate for full-load current. 430.22, conductors at 125 percent. 430.32, overloads from the nameplate. 430.52 and its table, branch-circuit short-circuit and ground-fault protection. 430.102 and 430.107, disconnect location and within sight. Tables 430.247 to 430.250 for full-load currents.
Article 450, Transformers
450.3(B) and its table, overcurrent protection for transformers 1000 volts and under, with the 125 and 250 percent rules and the notes that allow the next standard size. The primary and secondary current formulas, single and three phase. 450.9 ventilation, 450.13 accessibility and 450.21 for dry-type transformers indoors. Master exams add 240.21(C) secondary conductor protection and 250.30 grounding of separately derived systems, which together make up most of the transformer questions.
Chapter 9 tables
Table 1 for percent fill, Table 4 for raceway dimensions, Table 5 for conductor dimensions, Table 8 for conductor properties used in voltage drop. Annex C for the quick answer to how many conductors of one size fit in a raceway.
How to use this list
Tab each article. For each one, read the sections named here until you could explain them to an apprentice. Then work practice questions by article and log every miss by section number. After two weeks your log will show which three or four articles still need work, and those get the remaining hours. The rest of the code deserves a skim, not a study.