Which one is considered a primary distribution box

A primary distribution box is the main electrical distribution point that receives power from a transformer and distributes it to secondary distribution boxes or specific loads.OverviewA primary distribution box (also called a main distribution box or cabinet) is typically located in a distribution room or near a transformer. It serves as the central hub for distributing low-voltage power (commonly 0.4 kV) from the transformer to various secondary distribution points or directly to large equipment . Unlike secondary or tertiary boxes, it generally does not supply power directly to end-use devices but acts as the main control and protection point for the electrical system .Key CharacteristicsConnection to Transformer: Directly linked to the low-voltage side of a transformer, receiving three-phase power .Voltage Level: Typically handles 0.4 kV for distribution to buildings or major loads .Components: Includes main busbars, isolating switches, circuit breakers, and sometimes residual current devices (RCDs) for safety .Protection and Control: Equipped with metering systems, protective devices, and sometimes tie points for network flexibility .Physical Design: Often features bottom entry and exit cables, front-opening doors, and rainproof tops for outdoor installations .Load Distribution: Supplies power to secondary distribution boxes, which then distribute electricity to specific areas, floors, or equipment .Function in Electrical SystemsThe primary distribution box ensures safe, organized, and reliable power distribution. It allows for centralized control, fault isolation, and protection of downstream circuits. In larger systems, it may be part of a radial or looped primary distribution network, enhancing reliability by connecting multiple feeders and tie switches .Distinction from Secondary and Tertiary BoxesSecondary Distribution Box: Receives power from the primary box and distributes it to specific buildings, floors, or machinery, often handling three-phase loads .Tertiary Distribution Box: Supplies power directly to end-use devices, such as household outlets or small equipment, typically at single-phase 220V . In summary, the primary distribution box is the main distribution point in a low-voltage electrical system, providing centralized control, protection, and distribution to secondary systems while ensuring safety and operational efficiency.