300.5 Underground Installations
Table 300.5 Minimum Cover Requirements, 0 to 1000 Volts, Nominal, Burial in Millimeters (Inches)
|Type of Wiring Method or Circuit|
|Column 1 Direct Burial Cables or Conductors||Column 2 Rigid Metal Conduit or Intermediate Metal Conduit||Column 3 Nonmetallic Raceways Listed for Direct Burial Without Concrete Encasement or Other Approved Raceways||Column 4 Residential Branch Circuits Rated 120 Volts or Less with GFCI Protection and Maximum Overcurrent Protection of 20 Amperes||Column 5 Circuits for Control of Irrigation and Landscape Lighting Limited to Not More Than 30 Volts and Installed with Type UF or in Other Identified Cable or Raceway|
|Location of Wiring Method or Circuit||mm||in.||mm||in.||mm||in.||mm||in.||mm||in.|
|All locations not specified below||600||24||150||6||450||18||300||12||150a, b||6a, b|
|In trench below 50 mm (2 in.) thick concrete or equivalent||450||18||150||6||300||12||150||6||150||6|
|Under a building||0||0||0||0||0||0||0||0||0||0|
|(in raceway or Type MC or Type MI cable identified for direct burial)||(in raceway or Type MC or Type MI cable identified for direct burial)||(in raceway or Type MC or Type MI cable identified for direct burial)|
|Under minimum of 102 mm (4 in.) thick concrete exterior slab with no vehicular traffic and the slab extending not less than 152 mm (6 in.) beyond the underground installation||450||18||100||4||100||4||150||6||150||6|
|(direct burial)||(direct burial)|
|(in raceway)||(in raceway)|
|Under streets, highways, roads, alleys, driveways, and parking lots||600||24||600||24||600||24||600||24||600||24|
|One- and two-family dwelling driveways and outdoor parking areas, and used only for dwelling-related purposes||450||18||450||18||450||18||300||12||450||18|
|In or under airport runways, including adjacent areas where trespassing prohibited||450||18||450||18||450||18||450||18||450||18|
|aA lesser depth shall be permitted where specified in the installation instructions of a listed low-voltage lighting system.|
|bA depth of 150 mm (6 in.) shall be permitted for pool, spa, and fountain lighting, installed in a nonmetallic raceway, limited to not more than 30 volts where part of a listed low-voltage lighting system.|
|1. Cover is defined as the shortest distance in mm (in.) measured between a point on the top surface of any direct-buried conductor, cable, conduit, or other raceway and the top surface of finished grade, concrete, or similar cover.|
|2. Raceways approved for burial only where concrete encased shall require concrete envelope not less than 50 mm (2 in.) thick.|
|3. Lesser depths shall be permitted where cables and conductors rise for terminations or splices or where access is otherwise required.|
|4. Where one of the wiring method types listed in Columns 1 through 3 is used for one of the circuit types in Columns 4 and 5, the shallowest depth of burial shall be permitted.|
|5. Where solid rock prevents compliance with the cover depths specified in this table, the wiring shall be installed in a metal raceway, or a nonmetallic raceway permitted for direct burial. The raceways shall be covered by a minimum of 50 mm (2 in.) of concrete extending down to rock.|
Exception No. 1: Type MI cable shall be permitted under a building without installation in a raceway where embedded in concrete, fill, or other masonry in accordance with 332.10(6) or in underground runs where suitably protected against physical damage and corrosive conditions in accordance with 332.10(10).
Exception No. 2: Type MC cable listed for direct burial or concrete encasement shall be permitted under a building without installation in a raceway in accordance with 330.10(A)(5) and in wet locations in accordance with 330.10(A)(11).
Where necessary to prevent physical damage to the raceway, cable, or conductor, protection shall be provided in the form of granular or selected material, suitable running boards, suitable sleeves, or other approved means.
Informational Note: Presence of hazardous gases or vapors may also necessitate sealing of underground conduits or raceways entering buildings.
Exception No. 1: Conductors shall be permitted to be installed in parallel in raceways, multiconductor cables, or direct-buried single conductor cables. Each raceway or multiconductor cable shall contain all conductors of the same circuit, including equipment grounding conductors. Each direct-buried single conductor cable shall be located in close proximity in the trench to the other single conductor cables in the same parallel set of conductors in the circuit, including equipment grounding conductors.
Exception No. 2: Isolated phase, polarity, grounded conductor, and equipment grounding and bonding conductor installations shall be permitted in nonmetallic raceways or cables with a nonmetallic covering or nonmagnetic sheath in close proximity where conductors are paralleled as permitted in 310.10(G), and where the conditions of 300.20(B) are met.
Informational Note: This section recognizes "S" loops in underground direct burial cables and conductors to raceway transitions, expansion fittings in raceway risers to fixed equipment, and, generally, the provision of flexible connections to equipment subject to settlement or frost heaves.