Distribution boxes are organized hierarchically into main distribution boards, sub-distribution boards, and consumer units, each serving specific roles in safely distributing electrical power.

Main Distribution Board (MDB)

The Main Distribution Board is the primary control panel for an entire building or facility. It receives high-voltage, high-amperage power from the utility or main transformer and distributes it to sub-distribution boards and major electrical loads. Key components include the main incoming breaker, busbars, and outgoing feeders. MDBs are typically large, floor-standing enclosures designed to handle high fault currents and are used in industrial plants, commercial buildings, high-rise residential complexes, and power plants .

Sub-Distribution Board (SDB)

A Sub-Distribution Board is a secondary panel that receives power from the MDB and distributes it to specific areas, floors, or zones within a building. It allows localized control and protection of circuits, making maintenance and troubleshooting easier. SDBs contain circuit breakers or fuses for each branch circuit and are commonly used in multi-story buildings, factories, and large commercial facilities .

Consumer Unit

The Consumer Unit, often found in residential or small commercial settings, is the final level of distribution. It receives power from the SDB or directly from the MDB in smaller installations. Consumer units house miniature circuit breakers (MCBs), residual current devices (RCCBs), and isolators to protect individual circuits and ensure user safety. They are usually wall-mounted and designed for easy access .

Other Types and Components

• Meter Panels: Measure electricity consumption for billing or monitoring purposes.
• Panel Fuse Banks: Provide overcurrent protection for multiple circuits.
• Unitized Panels and Enclosed Switchgear: Used in industrial or critical facilities for advanced control and protection.
• Transfer Switches: Enable switching between utility and backup power sources for critical loads .

Key Components Across Levels

• Busbars: Conduct electricity within the box and distribute it to circuits.
• Circuit Breakers/Fuses: Protect circuits from overloads and short circuits.
• RCCBs/Isolators: Enhance safety by detecting leakage currents and allowing maintenance isolation.
• Enclosures: Made of metal or plastic, designed for indoor or outdoor use with appropriate IP ratings .

Selection Considerations

When choosing distribution boxes, consider:

• Installation environment (indoor vs. outdoor)
• Electrical load and number of circuits
• IP protection rating for dust and water resistance
• Material and durability (metal for industrial, plastic for residential) Understanding these levels ensures safe, organized, and efficient power distribution across all types of buildings and facilities .