Concealed secondary distribution boxes must meet accessibility, material, labeling, and installation standards to ensure safety, durability, and maintainability.

Accessibility Requirements

Secondary distribution boxes, including underground and handhole enclosures, must be installed so that wiring is accessible without removing parts of the building or excavating finished surfaces such as sidewalks or paving . Boxes cannot be concealed to the point where they are unknown or inaccessible, and access cannot rely solely on removing a luminaire unless the box is integral to the luminaire . This ensures safe troubleshooting and maintenance.

Material and Construction Standards

• Non-concrete enclosures: Must comply with Engineering Material Specification No. 51, with polymer concrete covers that are slip-resistant (coefficient of friction ≥ 0.65) and labeled with PG&E identification, manufacturer name, weight, and code number .
• Concrete enclosures: Required in areas subject to full vehicular traffic, meeting ASTM C-857 standards, with interchangeable joints and covers also slip-resistant and labeled .
• Pedestals: No longer allowed for new construction; replacement codes are specified in utility documentation .

Installation and Cover Requirements

• Cover depth: Minimum 24 inches for secondary (0–750 V) and 30 inches for primary (>750 V) underground installations, measured from the top of the final grade .
• Enclosure size selection: Based on the maximum conductor size and number to serve the service panel, and whether the area experiences incidental or full vehicular traffic .
• Labeling: All enclosures must display manufacturer information, weight, and utility code numbers on inside surfaces .

Modular and Concealed Systems

For raised floors or accessible ceilings, modular zone distribution systems can be used, combining pre-cut, pre-tested cables with plug-in connectors. These systems allow for easy adds, moves, and changes, improving cable management and reducing installation costs while maintaining accessibility .

Summary

Concealed secondary distribution boxes must be accessible, properly labeled, constructed from approved materials, and installed at appropriate depths. Compliance with utility specifications (e.g., PG&E) and electrical codes (e.g., NEC) ensures safety, maintainability, and durability, whether installed underground, under raised floors, or in accessible ceilings .