A junction box – also known as an ' electrical box ', ' jbox ', 'or ' terminal box ' – is a protective box where wires are interconnected. Junction boxes are often built into the plaster of a wall, in the ceiling, or within concrete. A small metal, plastic or fiberglass. The answer is simple, but profound: An electrical box is defined by its mission, not its material. It stripped away the jargon and gave us a “Golden Rule” for identifying these boxes instantly. Its primary function is to safeguard wires and prevent accidental contact, which can lead to short circuits or electrical fires.