California Code of Regulations
Title 8 - Industrial Relations
Division 1 - Department of Industrial Relations
Chapter 4 - Division of Industrial Safety
Subchapter 5 - Electrical Safety Orders
Group 2 - High-Voltage Electrical Safety Orders
Article 19 - Outdoor Wiring
Section 2827 - Raceways (or Ducts) Below Ground

(a) Protection Against Physical Damage. Underground ducts of rigid metallic steel conduit, Schedule 80 PVC conduit, or equivalent, containing cables operating at a potential above 35,000 volts, shall be installed at a depth of at least 36 inches. A lesser depth is permitted for ducts containing cables operating at 35,000 volts or less, if the duct is rigid metallic conduit, Schedule 80 PVC conduit, or equivalent, or if the duct has a layer of concrete at least 3 inches thick above the duct.

EXCEPTION: No. 1: Direct buried conduits to contain cables for series street lighting circuits operating at less than 7,500 volts shall be installed at a depth of at least 24 inches below the surface under which they are located.

EXCEPTION: No. 2: Where it is impractical to obtain the depth of cover specified, the depth shall be permitted to be reduced, provided that the duct has sufficient strength itself or adequate protection is installed above the duct to prevent damage to the duct system by any surface traffic.

(Title 24, Part 3, Section 3-710 - 3(b).)

(b) Protection Against Corrosion. Metallic underground ducts shall be suitably protected from corrosion.

(Title 24, Part 3, Section 300-6.)