What is the maximum number of 12 AWG conductors permitted in a 4 11/16 in. x 1 1/2 in. square box?

• A. 11 conductors
• B. 12 conductors
• C. 13 conductors
• D. 14 conductors

Answer: (C)

Box-fill is the key idea here. Each insulated conductor that originates outside the box and terminates or is spliced inside counts as one conductor. All equipment grounding conductors together count as one conductor, and any internal clamp counts as one conductor. For devices, the yoke or strap counts as one conductor.

A 4 11/16 in square box that’s 1 1/2 in deep has a internal volume of about 32.95 in³ (face area ≈ 4.6875" × 4.6875" ≈ 21.97 in²; multiplied by depth 1.5" gives ≈ 32.95 in³). For 12 AWG conductors, each requires 2.25 in³, so the box could hold up to about 32.95 / 2.25 ≈ 14.64 conductor-equivalents by volume, i.e., 14 conductors if there were no other considerations.

If a device is mounted in the box, its yoke counts as one conductor in the fill, reducing the number of insulated conductors you can add by one. That brings the maximum to 13 conductors. (Assuming no internal clamps are present; if there were included clamps, they would further reduce the count.)

So the maximum number of 12 AWG conductors permitted is 13.