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Standard diagram of a three-level electrical distribution box for construction sites

Fibre interconnection and data room reference Published 28 Jul 2025

Use this reference to prepare product questions for FD SOLUCIONES. Check interfaces, capacity, protection and installation requirements against the current product documentation.

A standard three-level electrical distribution system consists of a main distribution board, sub-distribution boards, and tertiary switch boxes, each with dedicated protective devices and hierarchical wiring to ensure safety and efficiency.

Overview of Three-

Level Distribution

A three-level electrical distribution system is designed to distribute power from a main source to multiple loads while maintaining hierarchy and safety. The levels are: Main Distribution Board (MDB): Receives power from the utility or transformer and contains the main protective device, typically an MCCB (Molded Case Circuit Breaker), which protects against overcurrent and short circuits.

The MD

B distributes power to sub-distribution boards via busbars or feeders, ensuring balanced load across phases (L1, L2, L3) and neutral connections.

Sub-

Distribution Boards (SDBs): These intermediate boards receive power from the MDB and further distribute it to tertiary switch boxes or directly to large equipment.

Each SD

B uses 3-pole MCBs for three-phase loads and may include RCCBs for additional protection. Busbars connect the main MCCB to the output MCBs, and neutral and earth links are provided for safety. Tertiary Switch Boxes: These are the final distribution points controlling individual equipment or sockets.

The principle of “one machine, one switch” is applied, meaning each switch box controls only one piece of equipment, with no cross-level bypassing. This ensures hierarchical integrity and simplifies maintenance.

Wiring and Safety Principles

Separate Circuits: Power and lighting circuits should be separated, even if housed in the same board, to prevent interference and overload. Minimized Distances: Distribution boards should be located close to the loads they serve. The distance from an SDB to a switch box should not exceed 30 meters, and from a switch box to its equipment preferably ≤3 meters.

Environmental Safety: Boards must be installed in dry, ventilated areas, away from harmful gases, moisture, or mechanical hazards. Adequate space for maintenance is required. Busbars and Connections: High-current connections use busbars instead of wires to handle large currents safely.

Proper earthing and neutral distribution are essential.

Diagram Representation

A simplified one-line diagram of a three-level distribution system includes: MDB: Main MCCB → Busbars → SDBsSDBs: 3-pole MCBs → Branch circuits → Tertiary switch boxesTertiary Switch Boxes: Individual MCBs → Equipment or socketsCodeCopyUtility / Transformer | MCCB (Main) | Busbars (L1, L2, L3, N) | --------------------- | | | SDB1 SDB2 SDB3 | | | MCBs MCBs MCBs | | |Switch Box Switch Box Switch Box | | | Equipment Equipment Equipment This diagram shows the hierarchical flow of power from the main source to individual equipment, maintaining the three-level structure and safety principles. Key ComponentsMCCB: Main protection for high current circuits.

MC

B: Branch protection for sub-circuits.

RCC

B: Optional residual current protection. Busbars: Conductors for high-current distribution. Neutral and Earth Links: Ensure safety and proper grounding.

By following this structure, a three-level distribution system ensures balanced load, safety, and ease of maintenance while complying with standard electrical design practices.

Standard diagram of a three-level electrical distribution box for construction sites - FD SOLUCIONES OPTICAL SYSTEMS [PDF]

Standard diagram of a three-level electrical distribution box for construction sites

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Technical note

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