314.28
Pull and Junction Box Sizing
Large conductors are stiff and have a minimum bending radius that must be respected to avoid damaging the insulation. Section 314.28 ensures that pull boxes and junction boxes are large enough to safely route and splice these big wires. For a straight pull — where the conductors enter one side and exit the opposite side — the box must be at least 8 times the trade diameter of the largest raceway. For an angle pull — where the conductors turn a corner inside the box — the distance from each raceway entry to the opposite wall must be at least 6 times the largest raceway in that row, plus the sum of the trade diameters of all other raceways entering on the same wall. These are minimum dimensions; larger boxes may be needed for practical wire management. If conductors are spliced inside the box, the angle-pull rules apply because the wires are effectively making a turn.
When You Need This
- Sizing a pull box for a large feeder run where the conductors need to change direction
- Designing a junction box in a commercial electrical room where multiple large conduits converge
- Verifying that an existing pull box can accommodate additional large conduits being added to it
- Answering exam questions about minimum box dimensions — these calculations appear frequently on licensing tests
Key Points
Common Mistakes
Using the 8x rule for an angle pull — 8x is for straight pulls only; angle pulls use the 6x-plus-others formula
Forgetting to add the trade diameters of the other raceways on the same wall during an angle pull calculation
Applying 314.28 rules to small conductors — these rules are specifically for 4 AWG and larger; smaller wires use 314.16
Measuring the outside dimension of the box instead of the inside dimension — the required distances are internal dimensions
Treating a splice box as a straight pull — any splice uses the angle pull calculation even if raceways enter from the same side
Exam Tip
Remember: 8x for STRAIGHT, 6x for ANGLE. For angle pulls, do not forget to add the trade sizes of the other raceways on the same wall. Exam questions often include multiple raceways entering the same wall to test whether you add them properly.
Frequently Asked Questions
Calculate both dimensions. Each side of the box must meet the minimum for the type of pull occurring at that entry. The box must be large enough to satisfy all the requirements simultaneously.
Conduit bodies must meet the same distance requirements unless they are marked by the manufacturer with the number and size of conductors they can accommodate. If the conduit body is marked, you can use it within those marked limits.
There is no code-specified maximum number of raceways, but each additional raceway increases the minimum box dimensions through the angle-pull formula. Practical and physical limitations will eventually dictate the maximum.
Related Code Sections
This is an educational summary, not the official code text. The NEC® is a registered trademark and copyright © National Fire Protection Association (NFPA). The CEC is copyright © CSA Group. For official code text, visit nfpa.org or csagroup.org. SparkShift is not affiliated with NFPA or CSA Group.