Configuration of three-level power distribution boxes for construction sites

Construction site power distribution boxes follow a three-level system with primary, secondary, and tertiary boxes, incorporating two-level leakage protection and the principle of one machine, one switch, one leakage, and one box.

Overview of Three-Level Distribution

Construction sites require temporary, mobile, and robust power distribution systems. The three-level configuration ensures safety, reliability, and compliance with construction electricity standards, forming a complete protection system for temporary power supply ( ).

Level I: Primary Distribution Box

• Purpose: Receives three-phase power from the transformer and distributes it to secondary boxes.
• Configuration:
  • Main circuit isolation with main circuit breaker and main fuse.
  • Shunt isolation with shunt leakage protection switch.
  • Equipped with N-line and PE-line terminal boards, ensuring proper grounding and neutral connections.
  • Includes voltmeter, total current meter, and other monitoring instruments.
  • Designed for high power (e.g., 580 kW) with armored aluminum core cables for incoming lines.
• Construction: Rainproof, dustproof, made of cold-rolled steel (1.5–2.0 mm thick), anti-corrosion treated ( ).

Level II: Secondary Distribution Box

• Purpose: Distributes power from the primary box to localized areas or temporary loads.
• Configuration:
  • Main circuit general isolation with fuse and circuit breaker.
  • Shunt isolation with shunt fuse and circuit breaker.
  • Inner and outer door design for safety and aesthetics.
  • Rainproof top suitable for outdoor use.
• Placement: Positioned near clusters of electrical equipment, typically within 30 meters of the primary box ( ).

Level III: Tertiary Distribution Box

• Purpose: Final junction box for individual electrical appliances or equipment.
• Configuration:
  • Isolation with leakage protector for each connected device.
  • Can be movable or fixed, depending on site requirements.
  • Ensures the principle of one machine, one switch, one leakage, one box to prevent multiple devices from being controlled by a single switch ( ).
• Placement: Horizontal distance from the switch box to the controlled equipment should not exceed 3 meters ( ).

Protection and Safety Measures

• Two-level leakage protection: Installed at both secondary and tertiary levels to prevent electric shock.
• Mechanical and environmental protection: Boxes are designed to withstand rain, dust, vibration, and rough handling, complying with IEC 61439-4 standards for construction site assemblies ( ).
• Monitoring: Meters and instruments in primary boxes allow real-time monitoring of voltage, current, and power consumption.

Material and Manufacturing Standards

• Box material: Cold-rolled steel or flame-retardant insulating materials.
• Steel thickness: 1.2–2.0 mm depending on box type.
• Surface treatment: Anti-corrosion and weatherproof.
• Certification: Products should comply with national standards and CCC certification ( ).

Summary

The three-level configuration ensures safe, reliable, and standardized temporary power distribution on construction sites. By combining primary, secondary, and tertiary boxes with two-level leakage protection and proper spacing, the system minimizes electrical hazards while providing flexible and efficient power supply for construction activities.