TradesHow this works
A pull box gives large conductors room to be drawn in and turned without a damaging bend. NEC 314.28 sets the minimums by the raceway sizes, not the conductor count. A straight pull needs a length of eight times the largest raceway. An angle or U pull needs six times the largest raceway in a row plus the trade sizes of the other raceways sharing that row.
Pick the pull type, enter the raceways, and the tool gives the minimum box dimension and the spacing to keep between the two entries that share a conductor. Run it on each wall that has an angle pull and take the largest result for each dimension. It gives the code minimum only, so confirm the box also fits the conductors, the fittings, and any splices.
Common questions
How do you size a pull box per NEC 314.28?
For a straight pull, the box length in line with the raceways must be at least eight times the trade size of the largest raceway, so a 3 inch raceway needs a 24 inch box. For an angle or U pull, the distance from a raceway entry to the opposite wall must be at least six times the largest raceway in that row plus the sum of the trade sizes of the other raceways in the same row.
When does the 314.28 rule apply?
It applies to pull boxes, junction boxes, and conduit bodies that contain conductors 4 AWG or larger. For smaller conductors, you size the box by the box-fill rules in 314.16 instead, which count conductors and devices rather than raceway sizes. This tool covers the large-conductor 314.28 case.
Why are angle pulls so much bigger than straight pulls?
A straight pull only needs length so the conductor can be drawn through, so it is governed by a single dimension. An angle or U pull makes the conductor turn inside the box, and it must turn without a sharp bend that would damage the insulation. That is why the code uses six times the raceway plus the neighbors rather than a simpler multiple, and why these boxes get large fast.
Sources: NEC (NFPA 70) Section 314.28(A) pull and junction box sizing (2023). Engine version 1.0.0. Risk tier 2.