What are the specifications for a secondary distribution box

Secondary distribution boxes are enclosures designed to safely manage and distribute electrical power from transformers to end-user circuits, with specifications covering materials, dimensions, installation, and modular configurations.

General Requirements

Secondary distribution boxes are used in underground or above-ground electrical distribution systems to connect transformer secondary outputs to service conductors. They must comply with all applicable building and safety codes, utility guidelines, and local authority requirements . For underground systems, contractors are responsible for providing and maintaining raceways and conductors to the secondary terminals, while utilities may install connectors and manage connections to the transformer .

Enclosure Materials and Types

• Concrete Enclosures: Required in areas subject to vehicular traffic; must meet ASTM C-857 standards for full-traffic applications .
• Non-Concrete Enclosures: Suitable for incidental loading; must comply with Engineering Material Specification No. 51 .
• Polymer Concrete Covers: Must have a slip-resistant surface with a high coefficient of friction (≥0.65) and PG&E-approved identification .
• Labeling: Enclosure body and cover must display manufacturer name, weight, and utility code number .

Dimensions and Installation

• Enclosures are available in various sizes to accommodate different numbers of service conductors and modular components .
• For installations exceeding the physical connection capacity of transformer secondary terminals, a separate padmounted connection enclosure is used .
• Modular zone distribution systems allow pre-cut, pre-tested cables and plug-in connectors for raised floor or accessible ceiling installations, improving flexibility and reducing installation costs .
• Compact secondary substations integrate medium voltage switchgear, distribution transformers, low voltage switchboards, and auxiliary equipment in a pre-fabricated enclosure for efficient secondary distribution .

Electrical Connections

• Compression Type Connectors: Used for connecting service conductors to transformer secondary terminals; approved connectors must follow utility guidelines .
• Service Lateral Conductors: Between transformer secondary terminals and connection enclosures, these are typically supplied and installed by the utility .
• Pre-Wired Modular Systems: Facilitate easy adds, moves, and changes in commercial or institutional facilities, enhancing cable management and lifecycle cost savings .

Safety and Compliance

• Enclosures must include proper marking, security devices, and identification to ensure safe operation and maintenance .
• Installation requires coordination with the utility, including easement agreements and project sketches showing conduit routes .
• All components must meet the latest utility and industry standards for electrical distribution, including load capacity, environmental protection, and accessibility . Secondary distribution boxes are therefore designed to provide safe, flexible, and code-compliant solutions for distributing electrical power from transformers to end-user circuits, with options ranging from simple underground enclosures to fully integrated compact substations and modular zone systems.