Junction boxes are an essential part of the electrical wiring systems for homes and buildings alike. The purpose of these boxes, which are often made from metal or plastic, is to house and safely protect a structure's electrical connections.

This sort of electrical casing typically comes in two sizes. Junction boxes that measure 2 inches x 3 inches, with a depth of 2.5 inches, generally contain three wires. Boxes that measure 2 inches x 3 inches and have a depth of 3.5 inches are made for five or more wires.

The electrical wires these boxes protect are known as hot (black), white (neutral), and grounding (green or copper). You may also see some other wire colors, which are used for secondary functions and lighting. A ROMEX, or an encased wire, runs from the main electrical panel (or a subpanel) to the junction box.

Within the junction box, wires are connected to the original ROMEX wire and are distributed to other fixture boxes. All wire gauges, or the measurement of wires' diameters, should be the same.

The junction box serves as the communal meeting spot for electrical wires, where they connect before moving on. All junction boxes must be covered, installed correctly, and in compliance with the applicable building codes. The cover protects the wires, keeps out dirt and dust, and prevents moisture from getting inside the box.