A junction box has 12 inches of length and must accommodate a straight-pull installation with 4 AWG conductors. What is the largest raceway size, in inches, that can be installed?

A junction box has 12 inches of length and must accommodate a straight-pull installation with 4 AWG conductors. What is the largest raceway size, in inches, that can be installed?

• A. 1 in.
• B. 1 1/2 in.
• C. 1 1/4 in.
• D. 2 in.

Answer: (B)

The main concept here is box fill and how conduit size uses space inside a junction box. When you pull conductors through a straight path in a box, every conductor displaces a portion of the box’s interior volume. NEC box-fill rules say you must have enough cubic inches inside the box to accommodate all conductors, the equipment grounding conductor, and any internal clamps. With 4 AWG conductors, each conductor takes a relatively large amount of space, and four current-carrying conductors plus a grounding conductor quickly add up in a 12-inch pull path. If the raceway bore is too large, it reduces the usable space available for those conductors, potentially exceeding the box’s fill limit or making the pull impractical. The largest raceway size that still fits the required four 4 AWG conductors (along with the grounding requirement) and allows a proper straight pull in that 12-inch length is 1 1/2 inches. A bigger raceway would not leave enough space for the conductors to pass through and be terminated correctly, while a smaller one would be more than enough space but isn’t the largest that can be installed.

The main concept here is box fill and how conduit size uses space inside a junction box. When you pull conductors through a straight path in a box, every conductor displaces a portion of the box’s interior volume. NEC box-fill rules say you must have enough cubic inches inside the box to accommodate all conductors, the equipment grounding conductor, and any internal clamps. With 4 AWG conductors, each conductor takes a relatively large amount of space, and four current-carrying conductors plus a grounding conductor quickly add up in a 12-inch pull path. If the raceway bore is too large, it reduces the usable space available for those conductors, potentially exceeding the box’s fill limit or making the pull impractical. The largest raceway size that still fits the required four 4 AWG conductors (along with the grounding requirement) and allows a proper straight pull in that 12-inch length is 1 1/2 inches. A bigger raceway would not leave enough space for the conductors to pass through and be terminated correctly, while a smaller one would be more than enough space but isn’t the largest that can be installed.