NEC Article 334 — NM Cable (Romex): Where It's Allowed and Where Hudson County Says No

NEC 334 covers NM cable — what we call "Romex." The standard wiring method in single-family residential, but its allowed-uses are tighter than most homeowners realize.

Where NM is allowed (334.10):

• One- and two-family dwellings — interior, dry locations
• Multi-family dwellings of Type III, IV, V construction (basically any wood-framed apartment)
• Other structures permitted to be of Types III, IV, V construction

Where NM is NOT allowed (334.12):

• Wet or damp locations — never. Need THHN/THWN-2 in conduit.
• Where exposed to physical damage — common in basement utility rooms with stuff stored against walls
• Embedded in masonry, concrete, or fill — never run through poured concrete
• In hazardous (classified) locations
• Buried — never directly buried
• In permanently moist locations — utility rooms with washers/dryers can be borderline

NJ Hudson County urban override: Jersey City, Hoboken, Bayonne, and Newark commonly amend the NEC to require conduit for ALL wiring including residential. The justification is fire-spread between attached/multi-family buildings. Always check with your local AHJ before running Romex on a Hudson County job — even single-family.

The 60 °C ampacity limit (334.80): NM-B insulation is rated 90 °C, but ampacity is limited to the 60 °C column of Table 310.16. So 12 AWG NM-B is rated 25 A (60 °C column) not 30 A (75 °C column). Doesn't matter much in practice because 240.4(D) limits 12 AWG to a 20 A breaker anyway, but matters for derating in hot attics.

Stapling and support (334.30): NM cable must be supported within 12 inches of every box and at intervals of no more than 4.5 ft. Plastic single-gang boxes have built-in clamps; bigger boxes use external clamps that must enter the box correctly.

For an EV charger run from main panel to a garage in Jersey City, use THHN/THWN-2 in EMT — the AHJ will reject Romex even though the run is in a single-family dwelling. EMT also handles the physical-damage requirement. See our conduit fill calculator at /tools/conduit-fill to size the EMT.