Junction boxes are the places in an electric circuit where two or more electric cables come together. They also serve as a support for switches, power receptacles or fixtures, and sometimes--particularly when cable is running through conduit--the box merely serves as a convenient and safe place to connect electrical wires. The most difficult part of connecting wires at a junction box is actually getting the wires to the box by running them above the ceiling or behind a wall. The actual connection at the box can be done in minutes.
Turn off the electrical power to the circuit you are working on.
Make the appropriate cuts for the junction box in the ceiling or drywall using the utility knife or saw. If you're feeding wire behind a wall or ceiling, make a small cut above the power source (normally an existing receptacle) where the wall meets the ceiling. If your circuit includes a switch, make a similar cut above the location of the switch. If you are using conduit, attach the conduit to the wall.
Attach the junction box to its support hardware. If you're using the box to hang a fixture like a fan or light, attach it to an expandable brace bar that will stretch between two joists above the ceiling. Do not rely on the strength of the ceiling to support any fixture. Light switch boxes and receptacle boxes can be attached to the drywall. In a conduit configuration, the junction box attaches to the conduit.
Feed the fish tape through the access holes and across the ceiling to the junction box. Attach the electrical cable to the fish tape and pull it back toward the access hole. Drop the cable down behind the wall to the source receptacle. For conduits, feed the fish tape through the conduit to the junction box and attach the cable. Pull the cable back toward you.
Make the connections at the junction box. In a fixture configuration, join the individual wires to the wires to the fixture with plastic connectors. Follow the circuit diagram that accompanies the fixture, which should be determined by the path of the current (e.g., from the source to the fixture to a switch). Attach the green ground wire to the junction box’s ground terminal with a screwdriver