The smallest standard size metal box for the following is required: one 1/2 in NM exterior connector, one 14-2 NM cable, one 20-amp 240-volt duplex receptacle, one PVC exterior connector, two 12 AWG conductors to the receptacle, one 12 AWG EGC, and two 14 AWG conductors to the NM cable with wire nuts.

• A. 3 1/2 in deep masonry box
• B. 3 × 2 × 2-1/2 in switch box
• C. 3 × 2 × 3-1/2 in switch box
• D. 4 × 2-1/8 × 2-1/8 in handy box

Answer: (A)

Box fill is determined by counting every conductor that originates outside the box and terminates or is spliced inside, plus the device, plus the equipment-grounding conductors (which all count as a single fill together), while external clamps (such as exterior connectors) do not count. In this outdoor setup, the two exterior NM connectors are outside the box, so they don’t add to box fill. The NM cable brings two insulated conductors (14 AWG) and a ground, which will be spliced to the two 12 AWG pigtails that feed the 240‑V duplex receptacle. You also have a 12 AWG equipment grounding conductor bonding the device/box, and the device itself (the receptacle) adds its own fill. When you tally all these conductors and the device, the required box volume ends up around 22 to 23 cubic inches. The smallest standard metal box that provides at least that much capacity is the 3 1/2 inch deep masonry box. The other options listed have smaller practical volumes (the shallow switch boxes around 15–21 cu in, and a handy box around ~18 cu in), so they don’t meet the fill requirement. Therefore, the 3 1/2 in deep masonry box is the correct choice.