⚡ QUESTION OF THE WEEK (2026) ⚡
#QuestionOfTheWeek2026:
An electrician is installing a metal outlet box that encloses the following wiring components:
- Three (3) #12 AWG THHN copper conductors originating outside the box and terminating on a duplex receptacle.
- Three (3) #12 AWG THHN copper conductors passing through the box without splice or termination.
- One (1) flush-mounted duplex receptacle device mounted on a single strap/yoke.
- Internal cable clamps inside the box.
- Two (2) #12 AWG copper equipment grounding conductors (EGCs) spliced together inside the box.
Using the 2026 NEC, determine the minimum box volume (in cubic inches) required to accommodate these conductors, clamps, devices, and grounding conductors.
🔎 Study Challenge: Don't just calculate it — find the information you need in the NEC first. Look for:
The section governing conductor fill, clamp fill, device fill, and grounding conductor fill allowances.
The rule for determining how many volume allowances each device yoke and equipment grounding conductor set requires.
The applicable Table used to determine the cubic-inch volume allowance per conductor size
💬 Comment your answer and identify the NEC section(s) or table(s) you used.
⚡ 2026 NEC FastTraxTube.com
⚡ Study Credit: TRADEHOG.NET
⚠️ Educational question. Verify applicable requirements using the NEC edition and local amendments.
Here is my calculation: Use Conductors 314.15(B), 314.16(A) Volume calculation, 314.16(A) Box Volume Calculation, 314.16(B) Box Fill Calculation, 314.16 B (1) Conductor fill, 314.16B (2) Clamp fill,
314.16 B (4) Device and Equipment fill, 314.16B (5). I figured the fist duplex Rec. the 3rd wire was an EGC, (That may be wrong).
Calculation: ( 3) #12 Connecting to a duplex Rec, I counted 1 as an EGC. 2x 2.25 = 4.50 Cu in
(3) #12 passing through 3x 2.25 = 6.75 Cu in
Duplex Rec. 2x 2.25 = 4.50 Cu in
EGC I counted 3 Which count as one of the biggest comin in 1 x2.25 = 2.25 Cu in
Clamps count as one of the biggest coming in 1x2.25 = 2.25 Cu in
________________
20.25 Cu in
Bill Budz Appreciate you breaking down the code sections, Bill! You nailed almost the entire layout and the EGC/clamp volume rules. The catch on the terminating conductors is that the prompt specified all three as current-carrying THHN conductors terminating on the device, with the EGCs counted separately in that final bullet. Adding that extra 2.25 cu in brings you right up to 22.5 cu in (Option C). Spot on with the 314.16 references otherwise! let me know if you spot any misconceptions in my interpretation!⚡