NEC Article 334: NM-B Cable (Romex) Rules
334.10 Where NM-B Is Permitted
NM-B is permitted in: one- and two-family dwellings, multifamily dwellings (Types III, IV, V construction), exposed or concealed in dry locations, in air voids of masonry block walls (if not damp). NM-B is the most common residential wiring method - it is inexpensive and quick to install.
334.12 Where NM-B Is NOT Permitted
NM-B is NOT permitted in: commercial buildings (generally), any building exceeding 3 floors, embedded in poured concrete or aggregate, in raceways (except as allowed by 334.15), exposed in dropped ceilings used as plenums, in wet locations, in hazardous locations.
These restrictions are why commercial work uses conduit or MC cable.
334.30 Securing and Supporting
NM-B must be secured within 12 inches of every box and at intervals not exceeding 4.5 feet. The cable must be clamped at boxes. Flat NM-B (like 14/2) must be stapled flat, not on edge. Staples must not crush the cable. In accessible attics, the cable must be protected or run through bored holes.
334.15 Protection from Damage
Through studs: bore holes at least 1-1/4 inches from the edge, or install nail plates. Through floor joists: same rules apply. Exposed runs in unfinished basements: run along the bottom of joists (not at an angle), or protect with running board. In garages, protect cable below 8 feet from damage.
334.80 Ampacity
NM-B is rated 90°C for conductor insulation but 60°C at the outer jacket. For ampacity, use the 60°C column of Table 310.16 unless all terminations are 75°C rated. This means 14 AWG NM-B = 15A, 12 AWG = 20A, 10 AWG = 30A. However, the 90°C conductor rating allows for higher derating capacity.
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Frequently Asked Questions
What does NEC Article 334 cover?
Article 334 covers nm-b cable (romex) requirements. Key sections include 334.10 Where NM-B Is Permitted and 334.12 Where NM-B Is NOT Permitted. It applies to all electrical installations in the United States.
Where can I find the full text of Article 334?
The full NEC is published by NFPA and available at nfpa.org. Many libraries provide free access. Your local building department also has copies available for reference during permit applications.
Does Article 334 apply to existing wiring?
The NEC applies to new installations, modifications, and additions. Existing wiring that was code-compliant when installed is generally grandfathered unless a renovation triggers an upgrade requirement. Check with your local AHJ (authority having jurisdiction).
When did the current Article 334 requirements take effect?
NEC 2023 is the current edition. Adoption varies by state. Check your state adoption status on our state code pages.
NEC 2023 references verified April 2026