NEC ReferenceNEC 2023 · 2026 · Updated Apr 2026

NEC Article 300: Wiring Methods & Burial Depths

NEC Article 300: Wiring Methods covers wiring methods by location through types compared. This guide explains each major section with practical interpretation for electricians.

300.3 Wiring Methods by Location

Indoor dry: NM-B (Romex), MC cable, conduit. Indoor wet: UF-B, THWN in conduit. Outdoor above grade: UF-B, conductors in rigid conduit. Underground: UF-B direct burial, THWN in conduit, direct burial cable. Commercial: typically conduit or MC cable (NM-B generally prohibited).

300.5 Burial Depth Requirements

Direct burial cable (UF-B): 24 inches. Rigid metal conduit (RMC): 6 inches. Intermediate metal conduit (IMC): 6 inches. PVC conduit: 18 inches. Under concrete slab: any conduit type at 0 inches. Under residential driveway: UF at 18 inches if GFCI protected.

300.4 Protection Against Physical Damage

Cables through studs: if edge of hole is less than 1-1/4 inches from edge of stud, install a nail plate. Cables in notches: protect with 1/16-inch steel plate. Cables in accessible attic: protect if within 6 feet of scuttle opening. Running boards required in certain attic configurations.

314.16 Box Fill

Every conductor, ground, clamp, and device counts against box fill. 14 AWG = 2.0 cubic inches each, 12 AWG = 2.25 each, 10 AWG = 2.5 each. A standard single-gang old-work box (14 cu in) can hold: three 14 AWG conductors + one device + ground. More conductors require a larger box.

Conduit Types Compared

EMT (Electrical Metallic Tubing): most common, lightweight, uses compression or setscrew fittings, provides ground path. PVC: for wet/corrosive environments, no ground path (must pull ground wire). RMC (Rigid Metal Conduit): heavy-duty, provides ground path, required for certain applications.

FMC (Flexible): for final connections to equipment.

Key NEC Tables Referenced

Frequently Asked Questions

What does NEC Article 300 cover?

Article 300 covers wiring methods requirements. Key sections include 300.3 Wiring Methods by Location and 300.5 Burial Depth Requirements. It applies to all electrical installations in the United States.

Where can I find the full text of Article 300?

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 300 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 300 requirements take effect?

NEC 2023 is the current edition. Adoption varies by state. Check your state adoption status on our state code pages.

Requirements vary by state. NEC edition, licensing, permits, and GFCI rules differ by jurisdiction. Check your state or pick it below for personalized info across WireRef.
This guide provides practical interpretation of NEC requirements. Always verify with your local AHJ and the current NEC edition adopted in your jurisdiction. WireRef is a reference tool and does not replace licensed professional judgment.

NEC 2023 references verified April 2026