How to Install an Electrical Junction Box

Junction boxes are typically used for adding another wire into a single electrical circuit. The metal or plastic box can also be used to reattach or repair a broken wire. Typically a household wire system will use a cable assembly called Romex. A Romex cable assembly is sheathed with an outer covering of insulation. Underneath the plastic covering are the current-carrying wires. Romex comes in a three-wire and a two-wire configuration for most home usage. A two-wire cable contains an insulated black and white wire with a bare copper wire for the earth grounding safety. The three-wire cable contains the same wires but has an additional insulated red colored wire. By following a basic process you can install the junction box and wires.

Things You'll Need

• Round metal junction box with cable clamps 1-inch long wood screws Screwdriver Wire cutters Pocketknife Wire strippers Wire pliers Wire nuts Round junction box cover

Instructions

The Steps

1. Remove all electrical power from the circuit. Attach the junction box to a firm wood frame. Use two wood screws and secure the box using the screwdriver. Cut the wires in half, centering on the junction box, using the wire cutters. Clean any broken ends of the wires if they are being repaired.

2. Remove the knockout opening for the insertion of the wires or Romex cabling. Generally one set of wires can enter through one knockout opening. Stick the end of the screwdriver into the slot of the knockout and twist. The metal plug will come free.

3. Push the wires or Romex through the hole in the box and allow six inches of the cable to protrude from the front of the box. Tighten the cable clamp securely around the wires.

4. Remove the outer insulation of the cable assembly with the pocketknife. Slit the plastic covering to the rear opening of the box. This will expose the full length, six inches, of the individually insulated wires. Use the wire strippers and remove three-quarters of an inch of the outer insulation to each wire, exposing the bare copper beneath.

5. Twist the appropriate pairs of wires together using the pliers. In other words, if you are repairing a break you will want to twist the black wire to the other black wire, the white to the white and the bare copper to the other bare copper wire. Individual wiring schemes will be different for various wiring connections.

6. Cover each twisted pair of wires with a wire nut. Install the junction box cover.

Tips & Warnings

• Some metal junction boxes may have a small green grounding screw. If so, attach a short, bare copper wire to this screw. The other end of the wire will be twisted with the bare copper connection already made in the box. Plastic junction boxes do not require a grounding wire. Some plastic junction boxes do not require a knockout to be removed. Simply push the wire through the one-way connector. Follow all state and local electrical codes.

References

• Install a Junction Box
• Junction Boxes