Pull & Junction Box Sizing Calculator

Determine minimum pull and junction box dimensions for conductors #4 AWG and larger per NEC §314.28. Covers 8× straight pulls, 6× angle pulls, and U-pulls.

NEC edition

Inputs

For straight pulls: min length = 8× largest conduit trade size

§314.28(A)(2) adds the trade size of every other raceway on the pull wall to 6× the largest

in

Trade sizes of raceways beyond the largest and the second, added together

U-pull: distance between conduit entries ≥ 6× trade size of largest opposite conduit

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⚡ Test your knowledge
NEC Article 220 was renumbered in the 2026 code cycle. What is the new article number?
  • A. Art. 100
  • B. Art. 120
  • C. Art. 200
  • D. Art. 230
💡 NEC 2026 renumbered Article 220 (Branch-Circuit, Feeder, and Service Calculations) to Article 120.
Energy Management Systems were moved from Article 750 to which article in NEC 2026?
  • A. Art. 100
  • B. Art. 125
  • C. Art. 130
  • D. Art. 150
💡 NEC 2026 moved Energy Management Systems from Article 750 to Article 130.
Which NEC standard size overcurrent device comes after 90A?
  • A. 95A
  • B. 100A
  • C. 110A
  • D. 105A
💡 Per NEC §240.6(A), the standard sizes are …90, 100, 110, 125… There is no 95A standard size.

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How it works & the NEC rules behind it

For electrical boxes and conduit bodies containing conductors #4 AWG or larger, NEC Section 314.28 establishes minimum dimensional sizing rules to prevent sharp bending radiuses that could damage thick cable insulation during pulling.

NEC §314.28 Sizing Rules:

  • Straight Pulls (§314.28(A)(1)): The length of the box shall not be less than 8 times the trade size of the largest raceway entering the box (e.g. 3" conduit = 24" minimum box length).
  • Angle Pulls & U-Pulls (§314.28(A)(2)): The distance between each raceway entry inside the box and the opposite wall must be at least 6 times the trade size of the largest raceway, PLUS the sum of the trade sizes of all other raceway entries on the same wall.
  • Distance Between Entries on Same Enclosure Wall: The distance between raceway entries containing the same conductor shall not be less than 6 times the trade size of the larger raceway.

Formulas & equations

Straight Pull Length = 8 × Largest Raceway Trade Size Angle / U-Pull Wall Distance = (6 × Largest Raceway) + Sum of Remaining Raceways Distance Between Same Conduit Entries = 6 × Largest Conduit Size

NEC reference table

Largest Raceway Trade Size Straight Pull Box Length (8×) Angle Pull Base Distance (6×) Conduit Entry Separation
1" Conduit8 inches6 inches6 inches
2" Conduit16 inches12 inches12 inches
2-1/2" Conduit20 inches15 inches15 inches
3" Conduit24 inches18 inches18 inches
3-1/2" Conduit28 inches21 inches21 inches
4" Conduit32 inches24 inches24 inches

Worked example, step by step

Example Calculation: Angle Pull with (1) 3" Conduit and (2) 2" Conduits

Scenario: Sizing a commercial NEMA 1 pull box where one wall has one 3" conduit and two 2" conduits entering for an angle pull.

  • Step 1 (6× Largest): 6 × 3.0" = 18.0 inches.
  • Step 2 (Add Remaining): 18.0" + 2.0" + 2.0" = 22.0 inches.
  • Step 3 (Box Selection): A standard 24" × 24" × 8" junction box satisfies the 22" requirement with ample room for bending.

Frequently asked questions

No. NEC §314.28 explicitly applies only to pull boxes and junction boxes containing conductors **#4 AWG and larger**. For smaller conductors (#6, #8, #10, #12, #14), standard volume-based box fill calculations under §314.16 apply.

Under NEC §314.28(A)(2) Exception and general requirements, the depth of the box must simply provide adequate clearance for locknuts, bushings, and conductor bending radiuses (typically at least the diameter of the largest entering conduit plus standard hub clearance).

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