Living room receptacle at trim-out

The answer

The box is overfilled: its contents require 20.25 cubic inches, but the box is marked 18.0 cubic inches.

Correct choice: 1. The box is too small for the cables and device it holds

Count it per 314.16(B) using Table 314.16(B) (12 AWG = 2.25 cu in): six insulated conductors from three 12/2 cables count 6; all the equipment grounding conductors together count 1; the receptacle yoke counts 2, based on the 12 AWG conductors connected to it. That is 9 x 2.25 = 20.25 cu in. Pigtails that start and end inside the box and the wire connectors do not count, and this nonmetallic box has no internal clamps. A box stuffed past its rating nicks insulation, strains splices, and traps heat when the device is pushed back in.

How to fix it

Code references

• NEC 2023 314.16 — Number of Conductors in Outlet, Device, and Junction Boxes, and Conduit Bodies

  Boxes shall be large enough to provide free space for all enclosed conductors, and the box volume per 314.16(A) shall not be less than the fill calculated per 314.16(B).

  Drills citing 314.16

• NEC 2023 314.16(B) — Box Fill Calculations

  Each conductor that originates outside the box and terminates or is spliced inside counts once; conductors that do not leave the box are not counted; each device yoke counts twice based on the largest conductor connected to it; all equipment grounding conductors together count once based on the largest.

  Drills citing 314.16(B)

• NEC 2023 Table 314.16(B) — Volume Allowance Required per Conductor

  Gives the volume allowance per conductor: 2.00 cu in for 14 AWG and 2.25 cu in for 12 AWG.

  Drills citing Table 314.16(B)

• NEC 2023 314.16(A)(2) — Other Boxes

  Boxes of 100 cu in or less not described in Table 314.16(A), and nonmetallic boxes, shall be durably and legibly marked by the manufacturer with their volume.

  Drills citing 314.16(A)(2)

2026 NEC:same rule and number. Rule and number kept. 2026 adds "splicing connectors" to the small fittings in 314.16(B) that need no box-fill allowance, which only confirms this drill's statement that wire connectors are not counted. Confidence: medium

Minnesota

Why the other choices are wrong

• No more than two cables may enter a single-gang box. The Code has no cable-count limit for a box; box fill volume under 314.16 is what governs.
• A 15 A duplex receptacle may not be connected to 12 AWG conductors. 12 AWG is fine on a 15 A device, and Table 210.21(B)(3) allows 15 A receptacles on a 20 A circuit with more than one receptacle.
• Nothing. This installation is compliant. Counted per 314.16(B), the contents need 9 x 2.25 = 20.25 cu in, more than the 18.0 cu in marked on the box.