Minimum Depth Requirements for Installing Underground Electrical Circuits

February 11, 2007

Buried Electric

Before you begin any underground electrical wiring project, you must first get a locate to find out what is underground. To schedule a locate call 811 in all 50 states and you will be connected to your local locator service.

Now that the locate is done, you need to determine which wiring method you will use. Are you going to install direct burial wire or cable? Perhaps you will use rigid metallic conduit or PVC. They all have different cover 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 need 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 need 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 need 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 need 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 need 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 need 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 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.

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Written by Wayne Gilchrist · Filed Under Electrical Installations & Repairs

Comments

2 Responses to “Minimum Depth Requirements for Installing Underground Electrical Circuits”

E. Diehl on September 25th, 2007 9:32 pm

What are some ways to get a “pull cord” 300 ft. throught 3″ PVC Conduit? We are doing our own underground conduit in advance of the Elect. Co. putting in a Primary feed from street. We must supply a “pull tape” or other suitable strong “cord” for them to attach the Primary power cable, and then, for them to pull their entire cable throught to the new Ground level Transformer. Someone mentioned using a Shop Vac and a plastic bag tied to end of cord. Can you help describe these steps or are there other ways? Thanks, E. Diehl
John Lind on March 26th, 2010 10:10 am

Requirements for depth (if any) for communications cables such as telephone in streets and roadways..

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