The top of a distribution box should be connected to the main incoming power supply, typically a single-phase 230V AC supply for domestic use or a three-phase supply for industrial setups, through the main MCB or main switch.

Main Supply Connection

The distribution box receives power from the main electrical source, which is connected at the top of the box. For single-phase domestic installations, this is usually a 230V AC supply consisting of a phase (live) and neutral wire. The incoming supply is first connected to the main double-pole MCB or main switch, which acts as the primary protective device for the entire board. Once the main MCB is turned on, it distributes power to all downstream circuits via individual MCBs or RCCBs for safety and overload protection . For industrial or commercial installations, a three-phase supply may be used, typically 400V AC, with three live wires (L1, L2, L3) and a neutral. The main switch or MCB at the top of the distribution box should be rated according to the total load and short-circuit capacity of the system .

Safety and Standards

• Ensure the main MCB rating matches the expected load; for domestic single-phase systems, a 63A MCB is commonly used .
• The incoming supply should be clearly marked as AC or DC and indicate the voltage level to prevent wiring errors .
• Proper grounding and neutral connections are essential to prevent electrical hazards.
• Follow local electrical codes and standards (IEC, NEC, or regional regulations) for installation and protection devices .

Summary

In essence, the top of the distribution box is where the main power enters, connected through a main switch or MCB. The supply type depends on the installation: single-phase 230V AC for homes or three-phase AC for industrial/commercial setups, with appropriate protective devices installed to ensure safety and compliance .