Per 314.16(B), a general-use dimmer switch counted in a single-gang box on a circuit wired with 12 AWG copper conductors is counted as how many conductors?

• A. 1 conductor (2.25 in.³)
• B. 2 conductors (4.50 in.³)
• C. 3 conductors (6.75 in.³)
• D. 4 conductors (9.0 in.³)

Answer: (B)

The key idea is how box-fill is calculated: count every conductor that originates outside the box and terminates or is spliced inside. A general-use dimmer in a single-gang box typically has two conductors that connect to it—the incoming hot and the outgoing switched leg to the light. Each of those conductors originates outside the box and is terminated on the device, so they both count toward box-fill. With 12 AWG copper, each counted conductor requires 2.25 cubic inches of space, so two conductors need 4.50 cubic inches. This is why the correct count is two conductors (4.50 in^3). If grounding conductors are present, they add to the total as one combined conductor, but they aren’t part of the two-conductor device count itself.