Requirements for Installing Underground Electrical Circuits

Before you begin any underground electrical wiring project, you must first get a location to find out what is underground. Now that the location is done, you need to determine which wiring method you will use. Are you going to install a direct burial wire or cable?

Perhaps you will use a rigid metallic conduit or PVC. They all have different coverage requirements.

For installations in a trench below 2 inches (50mm) thick concrete or equivalent:

  • Direct Burial Cables or Conductors need to be 18 inches (450mm) deep.
  • Rigid Metal Conduit or Intermediate Metal Conduit needs to be 6 inches (150mm) deep.
  • Nonmetallic Raceways Listed for Direct Burial Without Concrete Encasement or Other Approved Raceways need to be 12 inches (300mm) deep.
  • Residential Branch Circuits Rated 120 Volts or Less with GFCI Protection and Maximum Overcurrent Protection of 20 Amperes need to be 6 inches (150mm) deep.
  • 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 need to be 6 inches (150mm) deep.

For installations under a minimum of 4 inches (102mm) thick concrete exterior slab with no vehicular traffic and the slab extending not less than 6 inches (152mm) beyond the underground installation:

  • Direct Burial Cables or Conductors need to be 18 inches (450mm) deep.
  • Rigid Metal Conduit or Intermediate Metal Conduit needs to be 4 inches (100mm) deep.
  • Nonmetallic Raceways Listed for Direct Burial Without Concrete Encasement or Other Approved Raceways need to be 4 inches (100mm) deep.
  • Residential Branch Circuits Rated 120 Volts or Less with GFCI Protection and Maximum Overcurrent Protection of 20 Amperes need to be 6 inches (150mm) deep for direct burial or 4 inches (100mm) deep in a raceway.
  • 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 need to be 6 inches (150mm) deep.

For installations under streets, highways, roads, alleys, driveways, and parking lots:

  • Direct Burial Cables or Conductors need to be 24 inches (600mm) deep.
  • Rigid Metal Conduit or Intermediate Metal Conduit needs to be 24 inches (600mm) deep.
  • Nonmetallic Raceways Listed for Direct Burial Without Concrete Encasement or Other Approved Raceways need to be 24 inches (600mm) deep.
  • Residential Branch Circuits Rated 120 Volts or Less with GFCI Protection and Maximum Overcurrent Protection of 20 Amperes need to be 24 inches (600mm) deep.
  • 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 need to be 24 inches (600mm) deep.

For installations under one- and two-family dwelling driveways and outdoor parking areas and used only for dwelling-related purposes:

  • Direct Burial Cables or Conductors need to be 18 inches (450mm) deep.
  • Rigid Metal Conduit or Intermediate Metal Conduit needs to be 18 inches (450mm) deep.
  • Nonmetallic Raceways Listed for Direct Burial Without Concrete Encasement or Other Approved Raceways need to be 18 inches (450mm) deep.
  • Residential Branch Circuits Rated 120 Volts or Less with GFCI Protection and Maximum Overcurrent Protection of 20 Amperes need to be 12 inches (300mm) deep.
  • 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 need to be 18 inches (450mm) deep.

For installations under a building:

  • Direct Burial Cables or Conductors need to be 0 inches (0mm) deep (in raceway only)
  • Rigid Metal Conduit or Intermediate Metal Conduit needs to be 0 inches (0mm) deep.
  • Nonmetallic Raceways Listed for Direct Burial Without Concrete Encasement or Other Approved Raceways need to be 0 inches (0mm) deep.
  • Residential Branch Circuits Rated 120 Volts or Less with GFCI Protection and Maximum Overcurrent Protection of 20 Amperes need to be 0 inches (0mm) deep (in raceway only)
  • 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 need to be 0 inches (0mm) deep (in raceway only)

For all installations not specified above:

  • Direct Burial Cables or Conductors need to be 24 inches (600mm) deep.
  • Rigid Metal Conduit or Intermediate Metal Conduit needs to be 6 inches (150mm) deep.
  • Nonmetallic Raceways Listed for Direct Burial Without Concrete Encasement or Other Approved Raceways need to be 18 inches (450mm) deep.
  • Residential Branch Circuits Rated 120 Volts or Less with GFCI Protection and Maximum Overcurrent Protection of 20 Amperes need to be 12 inches (300mm) deep.
  • 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 need to be 6 inches (150mm) deep.

I don’t believe that I need to explain how to install your conduit or cable from point A to point B. However, I may be able to offer some tips.

Tip # 1 – When installing a PVC conduit, it is easiest to glue your conduit together before you place it in the ditch.

Tip # 2 – When you place the PVC conduit in the ditch, be sure the bottom of the ditch is fairly level. If there are large rocks or deep valleys in certain spots, when you backfill, the PVC will pull apart at the nearest coupling. This defeats the purpose of installing the conduit in the first place.

Worked in IT for 10 years, specialising in computer measurement, resource and performance management and complex problem solving. Changed careers to HVACr in 2015.

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