Which option best describes the smallest box assembly required to house a duplex receptacle fed by MC cables with two hots and two neutrals?

• A. 4 × 21/8 square box with a 3.6 in3 plaster ring
• B. two - 3 × 2 × 2 device boxes (ganged)
• C. 4 × 11/2 square box with a 5.0 in3 plaster ring
• D. two - 3 × 2 × 21/2 device boxes (ganged)

Answer: (C)

The key idea is box-fill: count every insulated conductor that leaves or enters the box, add one for all grounding conductors, and add the device’s own contribution. For a duplex receptacle fed from MC cable with two hots and two neutrals, there are four current-carrying conductors inside the box, plus grounding conductors (count as one total), and the receptacle itself counts as two conductor units. With 14 AWG conductors (2.0 in³ per conductor), the required box fill is (4 + 1 + 2) × 2.0 = 14 in³.

Among the options, the combination with a 4 × 11/2 square box plus a plaster ring of 5.0 in³ provides enough total volume to meet or exceed 14 in³, while remaining a single-box assembly. The other single-box option with a smaller ring would not provide sufficient space, and the split or ganged box arrangements are larger than necessary for a single duplex. Therefore, the smallest suitable assembly is the 4 × 11/2 square box with the 5.0 in³ plaster ring.