5.6 Pull Boxes, Cabinets, Cutout Boxes & Accessibility (0402)

When 314.28 Applies

Section 5.2 established the trigger: 314.28 applies to boxes and conduit bodies used as pull or junction boxes where conductors of 4 AWG or larger are installed, and to conduit bodies with provisions for more than two conduit entries. Below 4 AWG, a conduit body is filled by volume under 314.16(C) instead.

The reason for the dimensional rules is mechanical, not thermal. Large conductors have a minimum bending radius; forcing 500 kcmil around a tight corner damages the insulation and can crack the conductor strands. The 8× and 6× multipliers are the Code's way of guaranteeing enough room to make the bend.

The Two Calculations

Straight pulls — 314.28(A)(1)

The length of the box or conduit body shall not be less than 8 times the trade size of the largest raceway.

A 3 in. raceway entering one end of a box and leaving the opposite end requires a box at least 8 × 3 = 24 in. long.

Angle pulls, U pulls, splices, or tapped conductors — 314.28(A)(2)

Three separate dimensions must be checked:

1. The distance between each raceway entry inside the box and the opposite wall shall not be less than 6 times the trade size of the largest raceway in that row.
2. That distance shall be increased by the sum of the trade sizes of the other raceways in the same row on the same wall.
3. The distance between raceway entries enclosing the same conductor shall not be less than 6 times the trade size of the larger raceway.

Memory hook: straight is 8, turn is 6. The straight pull gets the bigger multiplier because the conductors must be pushed through in a line with no corner to help; the angle pull gets 6 but must then add up all the other raceways in the row.

Worked Example — An Angle Pull

A junction box receives, on its left wall, three raceways in one horizontal row: 3 in., 2 in., and 2 in. The conductors turn 90 degrees and leave through the bottom wall. All conductors are 350 kcmil, so 314.28 applies.

Left-wall to opposite-wall dimension (the box width):

• 6 × the largest raceway in the row: 6 × 3 = 18 in.
• Plus the sum of the trade sizes of the other raceways in that row: 2 + 2 = 4 in.
• Minimum width = 18 + 4 = 22 in.

Bottom-wall dimension (the box height): apply the same method to whatever raceways are in the bottom row. If a single 3 in. raceway leaves the bottom, the minimum height is 6 × 3 = 18 in. with nothing to add.

Distance between entries enclosing the same conductor: the 3 in. entry on the left and the 3 in. exit on the bottom must be at least 6 × 3 = 18 in. apart, measured between the entries. On a 22 in. × 18 in. box with the raceways at opposite corners, that is satisfied; on a box where both raceways crowd the same corner, it is not — and this third check is the one people forget.

Answer: the box must be at least 22 in. × 18 in., and the raceway entries must be positioned so the same-conductor entries are at least 18 in. apart.

Two more provisions round out the section: 314.28(A)(3) permits smaller dimensions for a listed box or conduit body marked with the maximum number and maximum size of conductors, and 314.28(B) requires that where conductors enter a box through a raceway and are not terminated or spliced in the box, each conductor be racked or cabled in an approved manner so it can be identified.

Accessibility — 314.29

Boxes, conduit bodies, and handhole enclosures must be installed so that the wiring contained in them can be rendered accessible without removing any part of the building or, in underground circuits, without excavating sidewalks, paving, earth, or other substantial surface. An exception permits listed boxes and handhole enclosures to be covered by gravel, light aggregate, or non-cohesive granular soil where their location is effectively identified and accessible for excavation.

This is a rule with teeth. A junction box buried above a hard-lid gypsum ceiling with no access panel is a violation, and so is a splice box in a wall cavity behind finished drywall. During a rough-in inspection, the practical question is: after the finishes go in, can somebody open this cover? Related rules: 314.25 requires each box and conduit body to have a cover, faceplate, lampholder, or luminaire canopy, and 300.15 requires a box or conduit body at each splice, outlet, switch point, junction point, or pull point in the first place.

Cabinets and Cutout Boxes — Article 312

Article 312 covers cabinets (the enclosure a panelboard sits in), cutout boxes, and meter socket enclosures. The provisions an inspector uses:

The 312.5(C) cable-securing rule is one of the most-cited defects in commercial work: a bundle of MC cables entering a panel through a single large knockout with one connector, rather than each cable secured, is a violation on its face.

Field sequence for a pull box. Identify the largest raceway in each row. Multiply by 8 for straight, 6 for a turn. Add the other trade sizes in the row for a turn. Check the same-conductor entry spacing. Then step back and ask whether anyone will be able to open the cover after the ceiling goes in.