Most-missed NEC mock exam question #1 of 5, from JCR's free 25-question NEC mock exam. 72% of students got this wrong. Try it with your code book open, then check your answer below.
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The answer: D, 21½ inches
For an angle pull, multiply the trade size of the largest raceway in the row by 6. Then add the trade size of every other raceway in that same row on the same wall.
(6 × 3) + 2 + 1½ = 21½ inches.
Step by step
- Largest raceway in the row: 3 inches.
- 6 × 3 = 18 inches.
- Other raceways in the same row on the same wall: 2 + 1½ = 3½ inches.
- 18 + 3½ = 21½ inches from that wall to the opposite wall.
Where the wrong answers came from
- 18 inches was the top wrong answer, picked by 36% of students. That is 6 × 3, only the first half of the rule. It leaves out the other two raceways.
- 24 inches is 8 × 3. That is the straight-pull rule, and this question is an angle pull.
- 27½ inches mixes the two rules: 8 × 3, plus 2 and 1½.
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Pull box sizing calculator (NEC 314.28)
Pick the type of pull and the raceways in one row on one wall. The calculator applies 314.28(A) of the 2020 NEC and shows the math.
Raceways in one row on the same wall (trade size):
Minimum distance to the opposite wall: 26 in.
6 × 4 in. (largest) + 2 in. (others in the row) = 26 in.
Two entries that enclose the same conductor must be at least 6 × the larger raceway apart: 24 in. for a 4 in. raceway.
Uses NEC 314.28(A): trade size counts as inches, 8 × the largest raceway for a straight pull, 6 × the largest plus the other raceways in the row for an angle or U pull. Applies to conductors 4 AWG and larger. Figure each row on each wall by itself. The biggest answer sets that dimension.
What 314.28(A) says
These sizes apply when raceways hold conductors 4 AWG or larger that are required to be insulated, or when cables hold conductors 4 AWG or larger. Use the trade size (metric designator) of each raceway as its diameter.
- Straight pulls, 314.28(A)(1): the box length must be at least 8 times the trade size of the largest raceway.
- Angle or U pulls, or splices, 314.28(A)(2): the distance from each raceway entry to the opposite wall must be at least 6 times the trade size of the largest raceway in a row, plus the sum of the trade sizes of all other raceway entries in the same row on the same wall.
- More than one row: figure each row by itself. Use the row that gives the largest distance.
- Same conductor in and out: raceway entries enclosing the same conductor must be at least 6 times the trade size of the larger raceway apart.
Straight pulls and U pulls
- Straight pull, same three raceways: the box must be at least 8 × 3 = 24 inches long. Only the largest raceway counts.
- U pull: same rule as an angle pull. In a U pull the conductors leave on the same wall they enter, so count the raceways they leave through too. If the 3-inch, 2-inch and 1½-inch raceways are the only ones in that row, it's still 21½ inches from that wall to the opposite wall.
- Raceways on more than one wall: figure each row on each wall by itself. The row that gives the biggest number sets the box size in that direction.
- Same conductors in and out: if conductors enter through a 3-inch raceway and leave through a 2-inch raceway, those two entries must be at least 6 × 3 = 18 inches apart.
Common questions
How big does a pull box need to be for 2-inch conduit?
It depends on the pull. A straight pull needs a box at least 16 inches long (8 × 2). An angle pull where 2-inch is the largest raceway in the row needs at least 12 inches to the opposite wall (6 × 2), plus the trade size of every other raceway in that row.
What is the 8 times rule for pull boxes?
For a straight pull, the box length must be at least 8 times the trade size of the largest raceway (314.28(A)(1)). A 4-inch raceway needs a box at least 32 inches long.
Do these sizing rules apply to small wire?
No. 314.28(A) applies when the conductors are 4 AWG or larger. For 6 AWG and smaller, box size comes from the box fill rules in 314.16.
Every section cited here is from the 2020 NEC. Get the 2020 NEC from JCR or open it online with a paid NFPA LiNK subscription. Find the NEC edition your state tests.
JCR checked every rule on this page against the 2020 NEC in NFPA LiNK on October 21, 2026.
Related guides: How much weight a ceiling box can hold (314.27) · Conduit fill calculation · The 5 most-missed NEC mock exam questions
The 5 most-missed NEC mock exam questions
- Pull box size for an angle pull (314.28) (this post)
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See all 5 most-missed questions on one page.
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