Secondary electrical distribution box inside the building on the construction site

Secondary electrical distribution boxes inside buildings on construction sites safely distribute power from the main supply to various equipment and outlets, ensuring compliance with safety standards and protection against environmental hazards.

Purpose and Function

A secondary electrical distribution box (also called a sub-distribution board) is installed inside a building under construction to distribute electricity from the main connection or primary distribution box to multiple circuits and equipment. It allows for controlled and safe power delivery to lighting, machinery, temporary outlets, and other electrical devices on site, reducing the risk of overloading a single circuit and improving operational efficiency.

Construction and Materials

These boxes are typically made from robust materials such as sheet steel or fire-resistant technopolymer, providing durability and protection against mechanical impacts and environmental factors. Many models are designed to meet IP55 or higher protection classes, ensuring resistance to dust and water jets, which is crucial in harsh construction environments. Some boxes include internal doors, powder-coated steel panels, and modular compartments for easy installation and maintenance.

Installation and Mounting

Secondary distribution boxes can be wall-mounted or installed on supports inside the building. They are usually pre-wired and may include residual current devices (RCDs), circuit breakers, and multiple socket types (CEE or earthed) to safely supply power to different equipment. Proper installation should follow manufacturer instructions and local electrical codes, ensuring that all connections are secure and that the box is accessible for inspection and maintenance.

Safety Considerations

Compliance with standards: Boxes should conform to IEC 61439 and IEC 60364 standards for low-voltage switchgear and controlgear assemblies. Overcurrent and leakage protection: Use RCDs with appropriate rated differential currents (e.g., ∆n ≤ 500 mA) to protect personnel and equipment. Environmental protection: Ensure the box has adequate IP rating to prevent dust and water ingress, especially in partially open or unfinished buildings.

Cable management: Use flexible, durable cables such as rubber or H07RN-F types, and employ cable drums to reduce trip hazards and facilitate safe power distribution.

Practical Applications

Secondary distribution boxes are ideal for: Temporary power supply for construction machinery and toolsLighting circuits inside buildings under constructionPowering temporary offices, workshops, or storage areas on siteFestivals, market areas, or other temporary installations where modular and reusable distribution is needed. By following these guidelines, secondary electrical distribution boxes provide a safe, efficient, and flexible solution for managing electricity inside buildings on construction sites.