Which item counts toward NEC box-fill as a clamp when inside a box?

• A. Grounding screw
• B. Device yoke
• C. Cable insulation
• D. Internal clamp

Answer: (D)

Box-fill is based on counting every conductor that occupies the box plus certain hardware inside the box. An internal clamp, which secures cables inside the box, is considered part of that occupying hardware and is counted as one conductor toward the box-fill calculation. That’s why it’s the correct choice.

Grounding screws aren’t counted as separate conductors; all equipment grounding conductors are tallied together as one conductor for box-fill. Cable insulation isn’t counted separately because it’s part of the conductor itself. A device yoke isn’t a clamp, though it can affect box-fill as a separate conductor in some cases; this question specifically asks about clamps, so the internal clamp is the item that counts.