Cable Buried directly in Earth
Reference Codes - NEC, NESE, IEEE
Depth of Burial
The Depth of burial shall be sufficient to protect the cable from damage imposed by expected surface usage.Burial depths as indicated in table considered adequate for supply cables or conductors, except as noted a, b, or c (See NEC Code 300.5)
Voltage
|
Depth
of Burial
|
|
Phase to
Phase
|
in
|
mm
|
0 to 600
|
24
|
600
|
601 to 50000
|
30
|
750
|
50001 and
above
|
42
|
1070
|
Exception:
- Street light cables operating at not more than 150V to ground may be buries at a depth not less than 18" (450mm)
- In areas were frost conditions could damage cables, burial depths should be greater.
- Lesser depth may be used where supplemental protection is provided. The Supplemental protection should be sufficient to protect the cable from damage imposed by expected surface usage.
- Where the surface is not to final grade, the cable should be placed to meet or exceed the requirements indicated above, both at the time of installation and when the surface is to final grade.
Trenching
The bottom of the trench should be smooth, undisturbed, well-tamped earth or sand. When excavation is in rock or rocky soils, the cable should be laid on a protective layer of well-tamped backfill. Backfill within 4 inches of the cable should be free of materials that may damage the cable. Backfill should be adequately compacted. Machine compaction should not be used within 6 inches of the cable.
A protective covering above the cable will warn excavators of the presence of an
underlying cable.
NEC-300.5(3) - Underground service conductors, that are not encased in concrete and that as buried under 18" or more shall have location identified warning ribbon placed in the trench, at-least 300mm above the underground installation.
Plowing
Plowing of cable should not result in damage to the cable from rocks or other solid materials. The design of cable plowing equipment and the plowing of cable should not
damage the cable by exceeding bend, sidewall pressure, cable tension, or other allowable limits.
Additional Information
A jacketed multiconductor is preferable to the installation of single-conductor cables to
ease installation and avoid crossovers.
Under vehicular and pedestrian traffic ways, it is good practice to pull cable through a conduit.
