A junction box is an electrical enclosure that houses one or more wiring connections. It is a standard electrical box that contains the connection of two or more circuit cables or wires. Junction boxes protect the electrical connections from the weather and accidental electric shocks. They are used in almost every modern electrical system, including commercial and residential systems. Some of the functions of a junction box include:

• Housing the splicing of wires
• Splitting off power from a single source to multiple outlets
• Protecting wiring from the elements or environment, which can sometimes be corrosive or otherwise harmful to wiring material
• Protecting wiring from unwanted tampering, whether malicious or unintentional

Junction boxes can be made of metal or plastic and can range from 2 ½” to 3 ½” deep. They must have a removable cover that is accessible at all times. Junction boxes are usually found mounted to the framing of a home or building and can be used in ceilings, under floors, or concealed behind an access panel. They are an integral part of a circuit protection system where circuit integrity has to be provided, as for emergency lighting or emergency power lines, or the wiring between a nuclear reactor and a control room. All junction boxes must be covered, installed correctly, and in compliance with the applicable building codes.