A three-level distribution box system uses main circuit breakers, isolation switches, leakage protectors, and monitoring devices across three hierarchical levels to safely distribute and control electrical power.

First-Level Distribution Box (Main Distribution Box)

The first-level distribution box serves as the main hub of the power system, typically installed near the power source. Key equipment includes:

• Main circuit breaker: Controls the overall power supply and provides overload and short-circuit protection.
• Main leakage protector: Ensures safety by preventing electric shocks and leakage currents.
• Voltmeter and ammeter: For monitoring voltage and current across the system.
• Main isolation switches: Allow safe disconnection of the entire system for maintenance or emergencies. This level centralizes management and monitoring of the entire site's electrical power, ensuring reliability and safety .

Second-Level Distribution Box (Branch Distribution Box)

The second-level distribution box distributes power from the main box to specific areas or large equipment. Typical equipment includes:

• Branch circuit breakers: Protect individual circuits from overloads and short circuits.
• Branch leakage protectors: Provide localized protection against leakage currents.
• Shunt isolation switches: Enable safe disconnection of specific branches without affecting the entire system. This level ensures that each branch circuit is independently protected and controlled, improving overall system reliability .

Third-Level Distribution Box (Switch Box)

The third-level distribution box is the final distribution point, directly supplying power to individual electrical equipment. Equipment commonly installed includes:

• Isolation switches: Allow safe disconnection of specific devices.
• Circuit breakers: Protect the connected equipment from overloads and short circuits.
• Leakage protectors: Provide the last line of defense against electric shocks.
• Movable or fixed switchgear: Ensures that each machine or group of similar machines is controlled independently, following the principle of "one machine, one switch, one leakage, one box, one lock" .

Additional Considerations

• Two-level protection: Combines leakage protection at both the main and final distribution boxes to enhance safety.
• Three-phase distribution boxes: Often used in industrial or high-power applications to balance loads across phases and protect large machines like motors, compressors, and heaters .
• Construction and installation: Boxes are designed to be rainproof, durable, and suitable for field work, with copper or aluminum busbars for reliable connections . By using this hierarchical setup, the three-level distribution system ensures safe, reliable, and efficient power distribution, minimizing the impact of failures and protecting both equipment and personnel.