NEC Wiring Methods and Raceways: Wet Locations, Support Rules, and Fill Limits

Regulation: NEC Articles 300, 348–362

Keywords: NEC wiring methods, EMT conduit NEC, wet location wiring NEC, conduit support spacing, flexible metal conduit NEC, NEC raceway fill limits, underground wiring NEC 300, liquid-tight conduit requirements

Core Concepts

• Location Classifications: Dry: protected from weather. Damp: partially exposed (covered porches, canopies). Wet: exposed to weather, in concrete, underground. Wiring method must match location rating.
• EMT: Permitted in most locations. NOT permitted where subject to severe physical damage or in cinder concrete (unless encased in 2 in of concrete). Support within 3 ft of boxes and every 10 ft.
• Flexible Metal Conduit (FMC): Not suitable for wet locations. Maximum 6 ft for most equipment connections. Support within 12 in of box and every 4.5 ft. Not always an acceptable EGC.
• RMC: Suitable for all locations including direct burial and concrete encasement. Support within 3 ft of boxes and every 10 ft.
• Underground Burial Depths: Direct burial cable: 24 in general. RMC/IMC: 6 in. PVC conduit: 18 in. GFCI-protected circuits under residential driveways: 12 in.

Exam Traps

• EMT is not permitted in wet locations unless specifically listed for wet location use — standard fittings are not watertight.
• FMC longer than 6 feet requires a separate EGC inside — the conduit itself cannot serve as the sole ground path beyond that length.
• LFMC and FMC are different products — LFMC is permitted in wet locations; FMC is not.
• PVC conduit requires an EGC inside — it is non-metallic and cannot serve as the ground path.
• Support intervals are measured from boxes/fittings, not from the last support point.

Memory Aid

Wet = RMC, LFMC, or listed wet-rated products. FMC = dry only, max 6 ft without separate EGC. Burial depths: direct burial 24 in, RMC 6 in, PVC 18 in.