Which code section governs counting a general-use dimmer as two conductors in a 12 AWG circuit?

• A. 314.16(B)
• B. 404.9(B)
• C. 600.7(A)(2)
• D. None of the above

Answer: (A)

The main idea here is how box fill is calculated. NEC 314.16(B) governs the amount of space needed inside a box or device enclosure by counting each conductor that originates outside the box and is terminated or spliced inside, plus the other fill factors like grounding conductors, clamps, and the device itself. In a box that contains a general-use dimmer, you typically have two insulated leads that enter the box from the dimmer and are connected to the supply and the load. Each of those leads counts as one conductor for box fill, so the dimmer contributes two conductor equivalents to the box-fill calculation. With 12 AWG conductors, each conductor requires 2.25 cubic inches of box volume, so two conductors amount to 4.5 cubic inches.

This section is the one that specifies how to account for conductors in box-fill calculations. The other sections cited pertain to different aspects of code requirements (like switching devices’ ratings or other device-related rules) and do not address how to count conductors for box fill in this scenario.