Leaving the right amount of wire in an electrical box is crucial for safety and code compliance. This deliberate excess, often called “slack” or “free conductor,” is a fundamental requirement in residential and. In general, you should leave at least 6 inches of wire in the junction box. I'll go into more detail below. ) of free conductor, measured from the point in the box where it emerges from its raceway or cable sheath, shall be left at each outlet, junction, and switch point for splices or the connection of luminaires or devices. When choosing one, check the IP or NEMA rating. A. Materials: Inspect the cable distribution box and its accessories (such as fixed brackets, screws, terminal blocks, etc.