Junction Box Sizing Calculator (NEC 314.28)
Construction & Home ImprovementCalculate the minimum junction box dimension for a straight or angle conduit pull, per NEC Article 314.28.
Minimum Box Dimension
Minimum required junction box length (straight pull) or distance to the opposite wall (angle pull), per NEC 314.28.
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Frequently Asked Questions
What is the difference between a straight pull and an angle pull?
A straight pull is where a conduit enters and exits the box in the same direction, on opposite walls. An angle pull, or U pull, is where the conduit changes direction inside the box, or enters and exits the same wall. Angle pulls need more room to protect the conductor from a sharp bend, so they use a different, larger formula.
How is the minimum dimension calculated?
For a straight pull, the minimum length is 8 times the trade size of the largest conduit entering that wall. For an angle pull, the minimum distance to the opposite wall is 6 times the trade size of the largest conduit in that row, plus the sum of the trade sizes of all other conduits in the same row.
Is this the complete NEC 314.28 requirement?
This covers the core straight-pull and angle-pull minimum dimension formulas, the most commonly needed calculation. NEC 314.28 also includes additional rules for box depth with multiple rows of conduit, and Table 312.6(A) provides alternate values for conductors instead of conduit trade size. For a complex or unusual pull configuration, consult the full code text or a licensed electrician.
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