Which factors determine the box fill in a box containing multiple conductors and devices?

• A. The number of current-carrying conductors
• B. The number of equipment grounding conductors (count as one)
• C. Internal clamps
• D. All of the above

Answer: (D)

Box fill is about how much volume in a box is needed to accommodate everything inside it. You count each conductor that originates outside the box and is terminated or spliced inside as one unit of volume. All equipment grounding conductors in the box are treated collectively as one unit. Internal clamps inside the box count as one unit. If there are devices installed, their mounting yokes count as one unit per device. In a box with multiple conductors and devices, you must include all of these elements in the calculation. Therefore, the option that accounts for current-carrying conductors, the grounding conductors counted as one, and the internal clamps (and, by broader understanding, device yokes as well) is the correct choice.