An electrical junction box is a container for electrical junctions, usually intended to conceal them from sight and to some extent to eliminate tampering. It can be a small metal or plastic container, such as those intended to form part of wiring, especially in buildings; in this type of application, it may form part of an electrical conduit wiring system, or may be buried in the plaster of a wall, concealed behind an access panel or cast into concrete with only the lid showing. It may or may not include terminals etc. for joining wires. A similar container used for joining wires to electrical switches or sockets is called a pattress.
The term may also be used for a larger item, e.g. of street furniture; in the UK, this is sometimes called a cabinet. See Enclosure (electrical).
Junction boxes form an integral part of a circuit protection system. In the event circuit integrity has to be provided, as may be necessary for emergency lighting or emergency power lines, or the wiring between a nuclear reactor and a control room. In such an event, the fireproofing afforded to the incoming or outgoing cables must also be extended to cover the junction box to prevent short circuits inside the box during an accidental fire.