Maximum capacity of a three-level distribution box

The typical capacity of a tertiary (third-level) distribution box is around 60A, with secondary distribution boxes often rated for higher currents depending on connected loads.Overview of Three-Level DistributionA three-level distribution system consists of:Primary distribution box – Main distribution point connected to the transformer (0.4kV). It generally does not supply power directly to devices and includes isolating switches, circuit breakers, and residual current devices (RCDs) for overall protection .Secondary distribution box – Serves specific buildings or floors, handling three-phase power and larger loads. It typically includes large three-phase circuit breakers and may have a main switch rated around 60A, with additional switches for lighting (16A) and appliances like air conditioners or water heaters (20A–60A) depending on the load .Tertiary distribution box – The final distribution point for individual units or equipment, supplying 220V single-phase power. Each device is protected by its own single-phase circuit breaker, usually rated around 60A for heavy appliances, with leakage protection included to ensure safety .Typical Current RatingsPrimary distribution box: Depends on total site load; often several hundred amperes.Secondary distribution box: Main switch typically 60A, with branch circuits for lighting and appliances ranging from 16A to 60A .Tertiary distribution box: Individual circuits for household or equipment, usually up to 60A, with single-phase breakers and residual current protection .Safety ConsiderationsEach level follows the principle of “one machine, one switch, one RCD, one box, one lock”, ensuring no single switch controls multiple devices .Two-level protection is often implemented, with leakage protection at both secondary and tertiary levels to prevent electrical hazards .The capacity of each box should be selected based on the planned power consumption of connected equipment to avoid overloads.In summary, a tertiary distribution box typically handles up to 60A, while secondary boxes are designed for higher currents to supply multiple tertiary boxes, and primary boxes handle the total site load with appropriate protection devices.