Bedroom rough-in, device box
What's wrong here?
- Nothing. This installation is compliant
- The NM cables are not secured to the box with a clamp or connector
- The NM sheath must be stripped back so it stops at the outside of the box
- Two 14/2 cables overfill an 18 cu in single-gang box
Show the answer and the code reference
The answer
Nothing is wrong. Clampless single-gang nonmetallic boxes are permitted when the NM is stapled within 8 in. of the box and the sheath extends at least 1/4 in. into the box.
Correct choice: 1. Nothing. This installation is compliant
Normally a cable must be secured to the box it enters, but the 314.17(B)(2) Exception covers single-gang boxes not larger than 2 1/4 x 4 in. mounted in walls or ceilings: if the cable is fastened within 8 in. of the box, measured along the sheath, and the sheath extends at least 1/4 in. through a cable knockout, the cable does not have to be secured to the box. That is why standard nail-on boxes have knockout tabs and no clamps. Each cable here is stapled a few inches above the box (also meeting the 12 in. rule in 334.30), runs in the center of the stud side, and the sheath shows inside the box past the tab. The tighter 8 in. distance is what to watch; a staple at 10 in. would be fine for 334.30 but would not qualify for the clampless exception.
How to fix it
No correction needed. Keep the staple within 8 in. of the box on clampless boxes, keep at least 1/4 in. of sheath inside the box, and use a box with clamps or connectors for larger multigang boxes.
Code references
NEC 2023 314.17(B)(2) Exception — Conductors and Cables Entering Boxes, Conduit Bodies, or Fittings
Where NM or multiconductor UF cable is used with single-gang boxes not larger than a nominal 2 1/4 x 4 in. mounted in walls or ceilings, the cable is fastened within 8 in. of the box measured along the sheath, and the sheath extends through a cable knockout at least 1/4 in., securing the cable to the box is not required; multiple cables may share one knockout. Otherwise 314.17(B)(2) requires the sheath to extend at least 1/4 in. into the box and beyond any clamp, and the cable to be secured to the box.
Drills citing 314.17(B)(2) ExceptionNEC 2023 334.30 — Securing and Supporting
NM cable shall be supported and secured by staples, listed and identified cable ties, straps, hangers, or similar fittings at intervals not exceeding 4 1/2 ft and within 12 in. of every cable entry into enclosures such as boxes.
Drills citing 334.30NEC 2023 314.16(B) — Box Fill Calculations
Each conductor entering from outside the box counts once, all equipment grounding conductors together count once, and each device yoke counts twice, using the per-conductor volumes in Table 314.16(B).
Drills citing 314.16(B)
2026 NEC:not yet checked Confidence: low
Minnesota
Minnesota adopts the NEC by reference without amendment (Minn. Rules 1315.0200; Minn. Stat. 326B.35), so 314.17, 314.16 and 334.30 apply as published. The 2023 NEC governs permits filed July 1, 2023 through Aug. 16, 2026; the 2026 NEC governs permits filed on or after Aug. 17, 2026 (exams moved to the 2026 NEC on Sept. 8, 2026). See the 2026 NEC note on this drill.
How Minnesota adopts the NECWhy the other choices are wrong
- The NM cables are not secured to the box with a clamp or connector. Under the 314.17(B)(2) Exception, a single-gang box no larger than 2 1/4 x 4 in. mounted in a wall needs no clamp when the cable is fastened within 8 in. of the box and the sheath passes at least 1/4 in. through a cable knockout.
- The NM sheath must be stripped back so it stops at the outside of the box. It is the opposite: the sheath must extend at least 1/4 in. into the box and beyond any clamp (314.17(B)(2); also 334.19, new in 2023).
- Two 14/2 cables overfill an 18 cu in single-gang box. Per 314.16(B): 4 insulated conductors, plus 1 for all the grounds, plus 2 for a device = 7 x 2.00 cu in = 14 cu in, under the 18 cu in marked.