The most common junction box wiring diagram includes two inputs and two outputs, allowing you to power two components from one power source with the help of just one junction box. This diagram also includes important information about phase and voltage. A junction box is an enclosure designed to house electrical connections, providing a safe and organized way to connect multiple wires and circuits. These boxes can be made from various materials, including metal and plastic, and are crucial in both residential and commercial electrical systems. When wiring up a junction box, the first thing to consider is which type of junction box to use.