Section 334.10/NM Cable Uses Permitted and Not Permitted
NEC 334.10 and 334.12 define where NM cable (Romex) is permitted and prohibited based on construction type and occupancy.
NM cable (Type NM, NMC, NMS) is permitted in one- and two-family dwellings and their attached/detached garages, and in multifamily dwellings of Types III, IV, and V construction. NM cable is prohibited in buildings exceeding three floors above grade, in commercial garages, in theaters, in hazardous locations, and embedded in poured concrete or aggregate. Section 334.12 lists specific prohibitions: NM cable must not be used as service-entrance cable, in commercial buildings of Types I and II construction, or in any location exposed to physical damage. NM cable must be protected where run through studs, joists, or rafters within 1.25 inches of the edge by steel nail plates.
Why this section exists
NM cable has a non-metallic outer jacket that does not provide the mechanical protection or fire resistance of metallic wiring methods (EMT, MC cable, rigid conduit). In Type I and II construction (steel and concrete), the building is designed to resist fire for extended periods, and the wiring method must not compromise that fire resistance. In commercial garages, the cable is exposed to vehicle damage and petroleum products. The restrictions balance the convenience and cost savings of NM cable against the fire and physical protection needs of each building type.
What plan reviewers look for
Plan reviewers check the construction type from the architectural code analysis and verify NM cable is permitted. They check the number of floors above grade (NM prohibited above three floors). They verify the occupancy does not include a prohibited use (commercial garage, theater, hazardous). For permitted uses, they check for nail plate protection where cables pass through framing members close to the edge.