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

• A. 4 conductors
• B. 6 conductors
• C. 8 conductors
• D. 10 conductors

Answer: (B)

Box fill is the key idea here. Each 12 AWG conductor that comes into the box from the outside counts as one conductor, and equipment grounding conductors counted together count as one. If a mounting device or internal clamps are present, they add to the count as well. The volume each 12 AWG conductor requires is 2.25 cubic inches, and this octagon box has a total volume of 18 cubic inches.

In a typical ceiling box with a light, you’ll usually have two cables entering (hot and neutral on each, giving four insulated conductors). All the equipment grounding conductors tied together in the box count as one conductor. Since the fixture mounts on the box, the mounting strap (the device yoke) also counts as one conductor. That gives: 4 (hots/neutrals) + 1 (grounds) + 1 (device strap) = 6 conductors.

Six conductors × 2.25 cu in each = 13.5 cu in, which fits well under the 18 cu in box volume. If you tried to push more, you’d run out of box space (or add internal clamps, which would add another count).