An inspector locates a single-gang receptacle box with one internal clamp, one 12 AWG NM cable with ground, and one receptacle. What is the total calculated free space for this installation?

An inspector locates a single-gang receptacle box with one internal clamp, one 12 AWG NM cable with ground, and one receptacle. What is the total calculated free space for this installation?

• A. 7 cu in
• B. 11 cu in
• C. 9 cu in
• D. 13 cu in

Answer: (C)

Box fill is determined by counting every conductor that enters and terminates or is spliced inside the box, plus the space taken by internal clamps and by the device itself. For 12 AWG conductors, each counted unit equals 2.25 cubic inches. In this setup: - Two insulated conductors (hot and neutral) count as two units: 2 × 2.25 = 4.50 cu in. - All equipment grounding conductors together count as a half unit: 0.5 × 2.25 = 1.125 cu in. - The internal clamp counts as one unit: 2.25 cu in. - The single receptacle device in a single-gang box counts as a half unit: 0.5 × 2.25 = 1.125 cu in. Total units: 2 + 0.5 + 1 + 0.5 = 4 units. Total box fill: 4 × 2.25 = 9 cu in. Total calculated free space = 9 cubic inches.

Box fill is determined by counting every conductor that enters and terminates or is spliced inside the box, plus the space taken by internal clamps and by the device itself. For 12 AWG conductors, each counted unit equals 2.25 cubic inches.

In this setup:

• Two insulated conductors (hot and neutral) count as two units: 2 × 2.25 = 4.50 cu in.

• All equipment grounding conductors together count as a half unit: 0.5 × 2.25 = 1.125 cu in.

• The internal clamp counts as one unit: 2.25 cu in.

• The single receptacle device in a single-gang box counts as a half unit: 0.5 × 2.25 = 1.125 cu in.

Total units: 2 + 0.5 + 1 + 0.5 = 4 units.

Total box fill: 4 × 2.25 = 9 cu in.

Total calculated free space = 9 cubic inches.