Secondary distribution boxes typically use duplex or triplex aluminum cables rated for 600 volts or less, with cross-linked polyethylene insulation suitable for direct burial or duct installation.

Common Cable Types

1. Duplex Cable
   • Configuration: One insulated phase conductor and one neutral conductor.
   • Use: Single-phase, two-wire systems (120V or 120/240V).
   • Material: Aluminum conductors (AAC or AAAC) with XLPE insulation.
   • Installation: Can be buried directly or installed in ducts .
2. Triplex Cable
   • Configuration: Two insulated phase conductors and one neutral conductor (bare or insulated).
   • Use: Single-phase, three-wire systems, commonly for residential or small commercial connections.
   • Material: Stranded aluminum conductors with cross-linked polyethylene insulation.
   • Installation: Suitable for underground service, ducts, or overhead service drops .
3. Quadruplex Cable
   • Configuration: Three insulated phase conductors and one neutral conductor.
   • Use: Three-phase, four-wire systems for industrial facilities or apartment complexes.
   • Material: Aluminum conductors with XLPE insulation.
   • Installation: Can be used for short-distance power distribution or overhead service drops .

Key Features

• Voltage Rating: Typically 600 volts or less for secondary distribution.
• Conductor Material: Aluminum is preferred for its lightweight, corrosion resistance, and good conductivity.
• Insulation: Cross-linked polyethylene (XLPE) or polyethylene (PE) for heat, UV, and moisture resistance.
• Neutral Identification: Often marked with yellow stripes or solid yellow; some designs allow black neutrals if specified.
• Installation Methods: Direct burial, ducts, or overhead service drops depending on the system layout and local regulations .

Considerations

• Ampacity: Must be calculated according to conductor size, insulation type, and installation conditions, following the National Electrical Code.
• Mechanical Strength: Stranded conductors improve flexibility and tensile strength, important for overhead or underground installations.
• Environmental Protection: Insulation and sheathing protect against abrasion, moisture, and chemical exposure, especially in urban or harsh environments. In summary, duplex and triplex aluminum cables with XLPE insulation are the most widely used types in secondary distribution boxes, providing reliable low-voltage service to residential, commercial, and light industrial customers while allowing flexible installation options .