What is a Junction Box?

Junction boxes are metal or plastic enclosures used as housings for wiring connections. The connections within are called branch circuits and usually represent the end of a conduit run. Junction boxes make wire access easy, since all one must do is remove the covering to make alterations, repairs, or additions to a conduit. Junction boxes also protect wiring from the elements or environment, which can sometimes be corrosive or otherwise harmful to wiring material. Finally, junction boxes protect wiring from unwanted tampering, whether malicious or unintentional.

Junction Box Wiring Basics

Essentially, a junction box houses wire connections in order to split off power from a single source to multiple outlets. For instance, a junction box might contain one wire power source that is connected through multiple wires to power several different lights.

Junction boxes are usually between 2 ½ to 3 ½ inches long and made of metal or hard plastic. The functional difference between plastic and metal depends whether or not the junction box is supposed to support any weight. Some metal junction boxes can support light fixtures; plastic junction boxes cannot withstand this weight. Additional differences include installation, in that plastic junction boxes are typically quicker and easier to install than metal ones. However, a standard junction box designed to simple cover wire splices can be either metal or plastic.

Wire Splices in Junction Boxes

All wire splices must be contained within a junction box for a building to meet electric code, although sometimes splices are missed and may present hazards as a result. Any exposed wiring can be dangerous, but exposed wire splices are especially prone to accident because they can be tripped over, expel sparks or misrepresent themselves be misperceived as playthings by children or pets. Junction boxes are helpful for wire splices because they also allow one to easily locate the wire splice area.