Can a third-level distribution box be connected to a third-level distribution box

A third-level (tertiary) distribution box should not be connected after another third-level distribution box; each tertiary box must directly supply its own electrical equipment according to the hierarchical distribution principle.Hierarchical Structure of Three-Level DistributionIn a standard three-level distribution system:Primary distribution box: Receives power from the transformer and distributes it to secondary distribution boxes. It does not directly supply end-use equipment .Secondary distribution box: Acts as an intermediate hub, distributing three-phase power to tertiary boxes or heavy loads. It also does not directly supply individual equipment .Tertiary distribution box: The final distribution point, supplying single-phase power (220V) directly to electrical equipment. Each tertiary box is designed to control and protect a specific device or set of devices, following the principle of “one device, one circuit breaker, one residual current device, one box” .Why Cascading Tertiary Boxes is Not AllowedAccording to electrical distribution standards:No bypassing of levels: Tertiary boxes must connect directly to the equipment they control. Connecting one tertiary box after another would bypass the intended hierarchical structure, compromising safety and protection .Protection and isolation: Each tertiary box includes its own circuit breaker and residual current device (RCD) to protect the connected equipment. Cascading tertiary boxes could result in multiple devices being controlled by a single upstream breaker, violating the “one machine, one switch” principle .Voltage and load considerations: Tertiary boxes are designed for specific voltage and load limits. Connecting them in series could lead to voltage drops, overloads, or unsafe conditions .Correct PracticeEach tertiary distribution box should be fed directly from a secondary distribution box.Branching from a secondary box to multiple tertiary boxes is allowed, but tertiary boxes should never feed other tertiary boxes .Maintain proper distances and environmental conditions for safety: tertiary boxes should be installed close to the equipment they serve, typically within 3 meters horizontally . In summary, tertiary distribution boxes are the final stage in a three-level system and must not be connected in series after another tertiary box. Doing so would violate hierarchical distribution principles, reduce safety, and compromise circuit protection.