Connect the incoming live (hot) wires from the main supply to the main switch terminals. • 3-phase 4-wire distribution system In this video, I'll show you step-by-step how to wire a distribution board (DB) safely and professionally. Fix the box securely to the wall, ensuring it's at an accessible. Understanding the wiring diagram of an electrical panel box is essential for electricians and homeowners alike, as it allows them to troubleshoot any electrical issues, carry out repairs, or make additions to the system. All the electrical sub circuits are originated from a Distribution Board.