Installing an Electrical Junction Box

Installing an Electrical Junction Box

Installing a Ceiling Electrical Junction Box


Installing a light fixture or outlet in the ceiling requires an electrical junction box to hold the wire connections and the fixture or device. Installing such a box in a finished ceiling can be a bit tricky; not only must you ensure the brace bar connects to the ceiling joists securely, but you must make sure the box does not sit too far into the attic or protrude into the room below.



Find the joists near where you want to install a ceiling electrical junction box by sliding a stud finder over the ceiling. Mark the positions of the joists nearest to where you want to install the box.



Place the open side of the ceiling junction box that came with an expandable brace kit against the ceiling where you want the box installed. Make the location between joists, not on a joist. Trace around the box.



Push the end of a jab saw through the ceiling drywall along the trace line. Use the saw to cut along the line to create a hole in the ceiling.



Insert the brace through the hole. Let the brace legs rest on the drywall inside the ceiling. Use your hand to twist the brace bar clockwise until you feel resistance, indicating that the brace legs have connected with the joists. Use an adjustable wrench to continue to ensure the teeth on the sides of the brace legs penetrate the joists.



Turn off the breaker to the circuit you intend to use as a power source. In most cases this will be an existing light switch or outlet box.



Position a non-contact voltage sensor against the power source to ensure that no electricity is present at the source. The sensor will beep or flash if electricity is present.



Remove the cover from the switch or outlet at your power source. Remove the screws from the top and bottom of the switch or outlet to release it from its junction box.



Loosen the terminal screws on the side of the outlet holding the wires to the outlet or switch. Remove the wires from the screws and set the device aside.



Access your attic and feed a length of 12/2 nonmetallic electrical cable, through the opening in the ceiling. Pull the cable across the ceiling to the wall above the junction box that holds your power source.



Look along the wall’s top plate for wires that feed down through a drilled hole above the power source junction box. Drill a hole through the top plate using a 3/4-inch spade bit and a cordless drill if a hole or wires do not exist.



Ask an assistant to feed a fish tape up through the power source junction box and into the attic through the hole in the top plate. Use a screwdriver to help guide the tip of the tape through the hole.



Attach the end of the 12/2 nonmetallic cable to the end of the fist tape. Secure the cable to the tape with electrical tape. Ask your assistant to pull the fish tape from the power source box in the wall. This feeds the end of the cable down the wall and out the box. Remove the electrical tape from the end of the fish tape to release the cable.



Place the open side of the ceiling junction box face down on a sturdy work surface. Place a screwdriver on one of the round knockouts in the box. Strike the screwdriver with a mallet to remove the metal knockout from the box and leave an open hole. Push a nylon cable lock connector into the hole.



Slip the U-shaped bolt that came with the kit around the brace bar in the ceiling opening. Grab the end of the cable at the ceiling hole and push it through the nylon cable lock in the junction box. Slip the box over the two ends of the U-shaped bolt. Use the nuts provided with the kit to secure the box to the bolt.



Leave the cable disconnected from the power source until you install a fixture or device in the ceiling electrical junction box.


Things You Will Need

  • Stud finder
  • Expandable braced box kit
  • Jab saw
  • Adjustable wrench
  • Noncontact voltage sensor
  • Screwdriver
  • 12/2 nonmetallic electrical cable
  • 3/4-inch spade bit
  • Cordless drill
  • Fish tape

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