This is the first and crucial connection—attach the incoming live wire (typically marked with brown or red insulation) to the main terminal in the distribution box. Before we dive into technical details, let's establish why this matters so much. That cable running from your main service entrance to. Analyze the incoming line part: Determine the incoming line source of the distribution box and the configuration of the incoming line circuit breaker, and understand the power supply method of the distribution box. Covers wiring, placement, standards, and expert tips for a compliant setup. A DB box, also known as a distribution board, is responsible for distributing electrical power to various circuits in a building or facility.