Construction elevator is equipped with a three-level power distribution box

A construction elevator equipped with a three-level power distribution box uses a hierarchical system of primary, secondary, and tertiary boxes to ensure safe, reliable, and protected power delivery.

Structure and Levels

Primary Distribution Box (Level I): This is the main hub of the construction site's power system. It receives three-phase power from the transformer and distributes it to secondary boxes. It includes main circuit isolation, main circuit breakers, fuses, and shunt isolation with leakage protection switches.

The primary box is typically located centrally and designed for outdoor use with rainproof tops and copper busbars for reliable connections. Secondary Distribution Box (Level II): Positioned closer to the construction elevator, often on the same floor or within 30 meters of concentrated electrical equipment, the secondary box redistributes power from the primary box to tertiary boxes or directly to equipment. It features inner and outer doors, circuit breakers, fuses, and shunt isolation, forming part of the two-level protection system.

Tertiary Distribution Box (Level III): This is the final connection point for the elevator's electrical equipment. It can be fixed or movable and includes a leakage protection switch to safeguard the elevator and operators. Each appliance or device is connected to a separate RCD (residual current device), following the principle of "one machine, one switch, one leakage, one box, one lock," ensuring no single switch controls multiple devices.

Protection and Safety

The three-level system implements two-level protection, with leakage protection installed both in the tertiary box and in the upper-level boxes. This ensures that any electrical fault is isolated quickly, minimizing risk to personnel and equipment. The hierarchical design prevents overloading and allows for clear isolation of circuits for maintenance.

Placement and Load Considerations

Distribution boxes are strategically placed near the equipment they serve. For construction elevators, a dedicated tertiary box is installed to handle its specific load, typically ranging from 50–150 kW per box. The main switch rating is determined based on the number of lower-level boxes and the elevator's power consumption.

Summary

A three-level power distribution box system for a construction elevator ensures safe, reliable, and code-compliant power delivery. The primary box manages overall site power, the secondary box distributes it to localized areas, and the tertiary box directly powers the elevator with dedicated protection. This hierarchical approach supports efficient operation, maintenance, and safety on construction sites.