A device box has three 14-2 NM cables with equipment grounding conductors entering through internal clamps, and one single-pole switch is installed. What minimum box volume is required?

解析

Six insulated conductors count individually, all equipment grounding conductors together count as one, all internal clamps together count as one, and the switch yoke counts as two, for 10 allowances. At 2.00 cubic inches for 14 AWG, 10 x 2.00 = 20.0 cubic inches. The 18.0 answer misses one allowance, 16.0 omits both the clamp and grounding allowances, and 22.5 uses the 12 AWG allowance by mistake.