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The Code Question of the Day (CQD) is NECA and ELECTRICAL CONTRACTOR Magazine’s flagship National Electrical Code (NEC®) public forum for the industry. The daily distribution of Q&A generates a lively dialogue and shares relative Code-based practical responses.
June 30, 2026
Hi CQD,
Are green wire nuts required for splicing equipment grounding conductors in a box? Thank you, Jason N.
June 29, 2026
Good morning, does a 4-inch square box with four 12 AWG circuit conductors, one equipment grounding conductor, and a single-gang device have enough volume to be code compliant under the NEC? I want to make sure I am applying the fill calculation correctly. Thanks, Doug P.
Good Morning Doug, and thank you for the question. Let’s look at 314.16(B) for box fill calculations. For your example, we will use a 1-1/2” deep 4” square box, with a volume of 21 cu. in. per 314.16(A)(2); if your box has a marked volume that would be used instead.
314.16(B) requires conductors originating outside the box that are terminated or spliced in the box to be counted once. Your question did not reference any looped conductors that would also need to be counted, so we will take 4- #12s @ 2.25 cu in per table (B)(4), totaling 9 cu in.
The device will be counted as 2x the largest conductor in the box, #12 in your example, so 2 x 2.25 for 4.5 cu in.
The grouding pigtail originates inside the box, and is not counted.
Totaling conductor volume (9 cu in) and device volume (4.5 cu in) totals 13.5 cu in; well below the 21 cu in box volume per the table.