Provides a return path for current, ensuring proper system operation. Outer casing that protects internal components from dust, moisture, and physical damage. You use a distribution box to divide electrical power into smaller circuits. The Distribution box system diagram mainly includes the following parts: Incoming line part: Displays the incoming line source of the distribution box, which may be a single-line incoming line or multiple-line incoming lines (such as normal power supply and backup power supply), and marks the. A distribution box, often simply called a DB, is a crucial component in any electrical installation.