NEC Tables · Wiring Methods

Table 300.5 — minimum burial depth

How deep the trench has to be — by what you’re burying and what’s on top of it.

Free · NEC 2023 · Updated
600 in.
All locations not specified below · mm
minimum cover per Table 300.5(A)
Exam trapRigid metal conduit is the cheat code: 6 in. of cover almost everywhere, 0 in. under a building. If a question offers RMC as an option, the answer usually shrinks.

Cover means the distance from the top of the cable or conduit to finished grade — not the trench depth. Location drives everything: the same direct-buried cable needs 24 in. under a street but can sit at 12 in. as a GFCI-protected residential branch circuit.

Location of Wiring Method or CircuitDirect Burial Cables or ConductorsRigid Metal Conduit or Intermediate Metal ConduitElectrical Metallic Tubing,Nonmetallic Raceways Listed for Direct Burial Without Concrete Encasement, or Other Approved RacewaysResidential Branch Circuits Rated 120 Volts or Less with GFCI Protection and Maximum Overcurrent Protection of 20 AmperesCircuits 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 Circuitmmin.mmin.mmin.mmin.mmin.
All locations not specified below60024150645018300121501,261,2
In trench below 50 mm (2 in.) thick concrete or equivalent4501815063001215061506
Under a building0000000000
(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 installation450181004100415061506
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 installation4501810041004(direct burial)(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 installation450181004100410041004
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 installation4501810041004(in raceway)(in raceway)
Under streets, highways, roads, alleys, driveways, and parking lots6002460024600246002460024
One- and two-family dwelling driveways and outdoor parking areas, and used only for dwelling-related purposes4501845018450183001245018
In or under airport runways, including adjacent areas where trespassing is prohibited4501845018450184501845018
Notes that change the answer — 300.5(A)

1 A lesser depth shall be permitted where specified in the installation instructions of a listed low-voltage lighting system.

2 A 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.

Notes:

1. Cover shall be 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 a 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.

6. Directly buried electrical metallic tubing (EMT) shall comply with 358.10.

Values derived from the 2023 National Electrical Code for exam study. Verify installations against the adopted code and local amendments.

Race your codebook — 3 lookups on this table

Q1

An installer is deciding whether a receptacle outlet can be placed on a 10-ampere lighting branch circuit in a dwelling. Which section specifically lists the loads that a 10-ampere branch circuit is prohibited from supplying?

  1. A 210.23(A)(2)
  2. B 210.21(B)
  3. C 210.23(A)(1)
  4. D 210.23(C)
Show answer & explanation

Correct: A — 210.23(A)(2)

210.23(A)(2) is the specific list barring receptacle outlets, fixed appliances, garage door openers, and laundry equipment from a 10-ampere circuit. 210.21(B) instead covers receptacle ratings generally and doesn't address the 10-ampere circuit restriction, while 210.23(C) governs 30-ampere circuits.

Q2

An electrician is wiring heavy-duty lampholders for fixed lighting in a commercial warehouse (not a dwelling unit) and wants to run them on a 30-ampere branch circuit. Which section specifically permits this load on a 30-ampere branch circuit?

  1. A 210.23(B)
  2. B 210.21(A)
  3. C 210.23(C)
  4. D 210.23(D)
Show answer & explanation

Correct: C — 210.23(C)

210.23(C) is the subsection that lists permissible loads for 30-ampere branch circuits, including fixed heavy-duty lampholders outside dwelling units. 210.23(B) covers 15- and 20-ampere circuits and 210.23(D) covers 40- and 50-ampere circuits, so neither governs a 30-ampere circuit; 210.21(A) addresses lampholder ratings generally, not what loads a 30-ampere circuit may serve.

Q3

A low-voltage suspended-ceiling power system is being installed for pendant luminaires. The load-side utilization conductors feeding the fixtures are copper and need to meet the code minimum size. Which section specifies this minimum conductor size?

  1. A 393.14(B)
  2. B 393.60
  3. C 393.100(B)
  4. D 393.100(A)
Show answer & explanation

Correct: D — 393.100(A)

393.100(A) sets the 18 AWG minimum (copper) for load side utilization conductors, with a 24 AWG allowance for Class 2 circuits under specific conditions. 393.100(B) instead covers the power feed bus rail conductor size, not the load-side utilization wiring, and 393.14(B) and 393.60 deal with insulated conductor installation and equipment grounding, not minimum conductor sizing.

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Direct Burial Wire NEC guide Article 300 practice questions 25 questions
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