NEC 314.28 Pull Box Sizing Lookup
Start with the pull condition. NEC 314.28 is not a cubic-inch box-fill check. It screens pull and junction box dimensions from raceway trade size, pull direction, and raceway-entry layout.
| Pull Condition | Field Rule | Field Meaning |
|---|---|---|
| Straight pull | 8 × largest raceway | Check the box dimension in the direction of the pull. Use the largest raceway trade size on that pull axis. |
| Angle pull | 6 × largest raceway + others in same row | Check the wall where raceways enter and the distance to the opposite wall. Add the other raceways in the same row on that wall. |
| U pull | 6 × largest raceway + others in same row | Use the angle-pull style calculation when conductors enter and leave from the same wall. |
| Splices | 6 × largest raceway + others in same row | When larger conductors are spliced, check the enclosure as a splice condition rather than a simple straight-pull-only condition. |
| Same-conductor raceway spacing | 6 × larger raceway | Where raceway entries enclose the same conductors, check the spacing between those entries as a separate field dimension. |
| Box-fill boundary | 314.16(B) vs 314.28 | Use the Box Fill Calculator for #18 through #6 AWG cubic-inch box-fill screening. Use NEC 314.28 review for larger pull/junction box layout. |
Straight Pull
Straight Pull Formula
For a straight pull, check the inside box dimension in the direction the conductors travel through the enclosure. The field screening formula is eight times the trade size of the largest raceway on that pull axis.
Formula
Minimum straight-pull dimension = 8 × largest raceway trade size
- Check each pull axis: A box with left-right and top-bottom straight pulls may need separate horizontal and vertical checks.
- Use trade size: The field multiplier is based on raceway trade size, not conductor ampacity or cubic-inch box volume.
Angle, U Pulls, and Splices
6× Plus Same-Row Entries
For angle pulls, U pulls, or splices, check each wall and row of raceway entries. Start with six times the largest raceway in that row, then add the trade sizes of the other raceways in that same row on the same wall.
Formula
Minimum wall-to-opposite-wall distance = 6 × largest raceway in row + other raceways in that same row
- Do not use 8× for angle pulls: The straight-pull multiplier is not the angle-pull formula.
- Same wall, same row matters: Do not add unrelated raceways from another wall or another row unless that row is the one being checked.
Spacing Check
Raceway Entry Spacing
Where raceway entries enclose the same conductors, the spacing between those entries is a separate NEC 314.28 field check. The screening distance is based on six times the larger raceway trade size.
Do not treat wall-to-opposite-wall box size as the only check. Raceway spacing can control the layout even when the box dimensions look large enough.
Box Fill Boundary
NEC 314.16 and NEC 314.28 Boundary
NEC 314.16(B) and NEC 314.28 answer different field questions. Box-fill volume checks ask whether the box assembly has enough cubic inches for the entered conductors, devices, grounding conductors, clamps, fittings, and listed ring volume. NEC 314.28 checks pull/junction box dimensions for larger conductor pull geometry.
When a Box Fill Calculator result says Needs NEC 314.28 Review, the field issue is not solved by adding cubic inches. The layout has moved into pull-box sizing and raceway-entry spacing review.
Worked Examples
Fast Field Examples
Straight pull
Largest raceway on the pull axis is 3 in. Minimum dimension in the pull direction screens as 3 × 8 = 24 in.
Angle pull row
Same row on one wall has 4 in, 2 in, and 1 in raceways. Minimum distance screens as 6 × 4 + 2 + 1 = 27 in.
Calculator Use
TradeHub Calculator Application
Use NEC 314.28 when the layout moves beyond cubic-inch box-fill math and into pull-box dimensions, raceway trade sizes, pull direction, and entry spacing.
Related TradeHub Calculators
Field Checks
Common Field Misses
- Using box-fill cubic inches for larger pull boxes: NEC 314.28 is a dimension and layout check, not a cubic-inch volume table.
- Forgetting the same-row adders: For angle pulls, U pulls, and splices, other raceways in the same row on the same wall can increase the required dimension.
- Skipping raceway spacing: Same-conductor raceway entries may need their own spacing check even when the enclosure body dimension looks acceptable.
- Using outside box dimensions: Field layout should confirm usable inside dimensions and actual raceway-entry placement.
Related References
Related NEC Field References
Source Scope
Source Alignment and Use Scope
This page is a field-reference summary for NEC 314.28 pull and junction box sizing concepts. It does not reproduce proprietary NEC text, replace manufacturer enclosure instructions, or approve a field installation.
Review the TradeHub Code Citation & Source Log for source alignment records and the TradeHub Methodology page for how field references are scoped.
Final layout must be verified against the adopted NEC cycle, raceway type, conductor count and size, enclosure listing, manufacturer markings, and local inspection authority.
FAQ
NEC 314.28 FAQ
When does NEC 314.28 apply?
Use NEC 314.28 for pull boxes, junction boxes, and conduit bodies where larger conductor pull geometry and raceway trade size control the enclosure dimensions.
What is the straight pull rule?
For a straight pull, check the inside box dimension in the direction of the pull. The field screening formula is eight times the largest raceway trade size on that axis.
How do angle pulls and U pulls get sized?
Check each wall and row. Use six times the largest raceway in the row, then add the trade sizes of the other raceways in that same row on that same wall.
Is raceway spacing separate?
Yes. Raceways enclosing the same conductors need a separate spacing check based on six times the larger raceway trade size.
Can the Box Fill Calculator size NEC 314.28 pull boxes?
No. The Box Fill Calculator screens NEC 314.16(B) cubic-inch volume for #18 through #6 AWG. Larger pull or junction box layouts need NEC 314.28 review.