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Practice question · NEC Table 300.19(A)
How Often Do You Support Conductors in a Vertical Raceway?
How often you support conductors in a vertical raceway is a Table 300.19(A) read, and the trap is treating a tall vertical run like a horizontal one. In a vertical raceway the conductors hang, so the Code sets support intervals by conductor size. The stem gives you the size. The table gives you the distance.
Exam-style question (Sparky QOTD)
Table 300.19(A): 8 AWG copper conductors in a vertical raceway must be supported at intervals not exceeding ___.
A. 50 ft
B. 100 ft
C. 200 ft
D. 25 ft
Answer: B) 100 ft. Table 300.19(A) covers 18 AWG through 8 AWG conductors in vertical raceways with supports at least every 100 feet, and 8 AWG is in that range.
Where to Find It
Open your Code book to Table 300.19(A) in Article 300. The table is organized by conductor size ranges. Find the range that contains the stem's conductor: 18 AWG through 8 AWG. Conductors in that range, run in vertical raceways, require supports at least every 100 ft — in the stem's wording, supported at intervals not exceeding 100 feet. Tab it in your book: Article 300, Table 300.19(A) — vertical runs get conductor supports; small wire = 100 ft.
Why 100 Feet
The stem fixes both variables the table cares about. The orientation is vertical — that is what puts you in 300.19(A) at all, because vertical runs get conductor supports. The size is 8 AWG copper. Eight AWG is the top end of the 18 AWG through 8 AWG range, so this conductor sits at the very edge of the range and still takes the range's interval: 100 feet maximum between supports.
Work the options against that read. Option A, 50 ft, has you supporting twice as often as the Code requires — safe in the field, wrong on the exam, because the question asks what the Code requires. Option C, 200 ft, stretches the interval to double the permitted maximum. Option D, 25 ft, is not close to this range's number at all. Only option B matches the table row the stem puts you in.
Notice the pattern you can reuse: this is the same skill as the burial-depth table. Article 300 is full of tables keyed to one or two stem facts — wiring method and column in the UF cable burial question, conductor size and orientation here. Find the row or column the stem's facts select, then read the single number it gives you.
The Trap
The trap is the boundary. Because 8 AWG is the largest conductor in its range, it is tempting to assume it must follow whatever rule comes next for bigger wire. The table does not grade on a curve: through 8 AWG means 8 AWG is included, at 100 feet. When a stem picks a size that sits exactly on a range edge, that placement is the test.
Exam Tip
The words "vertical raceway" in a stem should send you straight to Table 300.19(A) before you finish reading the question. Then it is one comparison: which size range holds the conductor? For 18 AWG through 8 AWG, the number to have on your tab is 100 ft.
Keep Drilling
This is one of 33 NEC topics. Sparky's 1,087 codebook-first questions drill all of them — every question a lookup rep with your book open, 15 minutes a day.