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 17 - Enclosures for Electrical Installations
Section 2805 - Vaults-General

(a) Strength. Vault structures shall have sufficient strength to withstand the loading to which they may be subjected and to support the equipment mounted therein.

(b) Wall Material. Vault interior walls shall be of assemblies of materials approved for not less than one-hour, non-combustible fire-resistive construction.

(c) Doors. Door openings to vaults shall be protected by approved one-hor rated fire door and frame assemblies.

(d) Ceiling Access. Vault ceiling access opening covers or grates weighing less than 100 pounds shall be securely fastened in place.Openings must be minimum of 26 inches diameter or 24 inches by 26 inches in size. Safe access shall be provided from the opening to the floor or other working surface.

(e) Ventilating Ducts. All ventilating flues or ducts shall be of noncombustible construction.

(f) Ventilating Openings. Ventilating openings shall not be through the vault door, except where door opens to outdoors.

(g) Adequate Ventilation. Vaults shall be provided with means for ventilation adequate to prevent equipment temperatures in excess of those at which the equipment may be safely operated.

(h) Drainage. Where drainage from sumps in vaults is to a sewage system, a suitable trap shall be installed capable of preventing the entrance of sewer gas into the vault.

(i) Foreign Pipes and Accessories. Any pipe or duct system foreign to the electrical installation shall not enter or pass through a transformer vault.

EXCEPTION: Piping or other facilities provided for vault fire protection, or for transformer cooling, are not considered foreign to the electrical installation.

(j) Material shall not be stored in transformer vaults.