In box fill calculations, how are internal clamps treated?

• A. They are ignored for box fill
• B. They count as one conductor
• C. They count as two conductors
• D. They count only if the clamp size is large enough

Answer: (B)

The main idea is that anything inside the box that takes up space must be counted in the box-fill calculation. An internal clamp is part of the box assembly and occupies volume, so it is included as a conductor-equivalent in the fill. For each internal clamp inside the box, you add one conductor to the count. This is true regardless of the clamp’s size, and it’s in addition to the insulated conductors and the grounding conductors (which together count as one). So, if there is one internal clamp, you add one to the total; if there are two clamps, you add two, and so on. Ignoring the clamp or counting it based on size would understate the required box volume.