Materials and methods: NM, MC and EMT, where each is allowed, how each is supported and protected, and the California amendment that decides it
In one paragraph
Three wiring methods do almost all residential and light-commercial work in California, and the code tells you exactly where each may go. Nonmetallic-sheathed cable (NM) is allowed in one- and two-family dwellings and in multifamily and other buildings of wood-frame construction types, concealed behind a fifteen-minute thermal barrier outside of dwellings, and only inside raceways in noncombustible Type I and II buildings; the California amendments print that rule and tie the construction types to the Building Code. Metal-clad cable (MC) goes almost anywhere NM cannot, including exposed and in commercial ceilings. Electrical metallic tubing (EMT) is the method for exposed work, wet locations with the right fittings and anywhere subject to damage. The lesson gives the uses-permitted and not-permitted lists, the support intervals (NM every 4½ feet and within 12 inches of a box; MC every 6 feet; EMT every 10 feet and within 3 feet of a box), the 1¼-inch nail-plate rule, and the local-amendment check that decides whether your city allows NM at all.
The rule
Under the 2025 California Electrical Code as amended, Type NM cable is permitted in one- and two-family dwellings and their attached or detached garages and storage buildings, in multifamily dwellings and other structures permitted to be of Types III, IV and V construction (concealed within a 15-minute thermal barrier in other structures), and in Types I and II construction only within raceways permitted there (334.10), with construction types as defined in the California Building Code; it is not permitted in the locations 334.12 lists, and its ampacity is the 60-degree column (334.80). Cables within 1¼ inches of the edge of framing need a steel plate at least 1/16 inch thick (300.4). NM is secured at intervals not exceeding 4½ feet and within 12 inches of every box (334.30); MC at 6 feet (330.30); EMT at 10 feet and within 3 feet of each termination (358.30). Local jurisdictions may adopt more restrictive standards when filed with the Building Standards Commission.
Why it matters
The wiring method is decided at the estimate, and it moves the price by half: a garage in NM is a different job from the same garage in EMT. Guess wrong and you either lose the bid to someone who knew NM was allowed, or fail the rough because your city does not allow it. The support and protection rules are the corrections inspectors write most, and every one of them is a number you can memorize.