Once you know how to splice electrical wires, you open a world of possibilities with home improvement. Electrical wire splicing allows you to remove or move a wall, add an outlet, move an outlet, move or add a ceiling light, refinish an existing space like a basement, tame dangling wires, and countless other projects that enhance your living space.
The method detailed here is the correct way to splice electrical wires per code. Spliced wires are not to be held together with electrician's tape. Electrical wires are never left on their own in the wall cavity or ceiling. Instead, all splices must be contained within a junction box and the individual wires attached with wire nuts. The box itself must remain accessible and cannot be hidden behind drywall or other building materials that would require removal to get to the box.
The junction box provides a safe environment for your splices, protecting them against impact and containing sparks and fire if anything should go wrong. While junction boxes may at first seem unwieldy and unnecessary, you will find that they are easy to work with and will make your work safer.
- Working Time: 30 minutes
- Total Time: 45 minutes
- Skill Level: Expert
- Materials Cost: $10 to $15
Tools and Supplies You Will Need
Rip Outer Sheathing From Wires
Make sure that you are joining two similar cables. Each cable must be the same in terms of function, the number of individual wires within the sheathing, and the gauge (thickness) of those wires. Modern wiring (even up to 50 years old or so) will have the gauge and number printed on the side.
A common example is to join 12/2 NM wire to 12/2 NM wire. The "12" refers to the gauge, or thickness, of the wire. The "3" refers to the number of wires within the casing excluding the bare ground wire.
Expose the wires within the tough outer plastic casing. Do not use a utility knife, as you risk cutting into the individual wires. Instead, use an inexpensive tool called a cable ripper.
Insert the cable into the hole on the cable ripper until it is about 6 inches in. Lightly press the ripper together and pull quickly back.
Strip Coating Off of Wires
Every wire, except for ground, will be plastic-coated. Use your wire stripper to remove the coating to about 1/2-inch back.
Stripped Cables and Wires
When the sheathing has been stripped, about 6 inches of wire protrudes beyond the edge of the remaining sheathing. All separating paper is pulled out and snipped. Wires are stripped back and are smooth, not nicked.
Knock Free the Junction Box Plugs
With a screwdriver, knock out the two opposing plugs from your metal junction box.
Use your pliers to pry off and completely remove the plugs. Often, you have to rock the plug back and forth several times before it will come free. Dispose of the plugs.
Insert the Wire Clamps on the Junction Box
Screw the wire clamps onto the junction box. Do this by first removing the tightening ring, then placing the clamp into the junction box. Screw the tightening ring back onto the clamp from the inside of the box. Use your pliers to tighten the clamps onto the box. Do not turn too hard or you may break the clamps.
Put the Cables in the Junction Box
Insert one cable into the junction box, through the clamp. Make sure that the cable is positioned flat on the clamp. If you accidentally position it sideways, you risk damage to the cable. Turn the screws on the clamp until the cable is secure.
Repeat on the other side. Insert the cable through with about 6 inches of free wire at the end. Screw down the clamp.
The sheathing section of the cables should extend into the junction box about 1/4-inch.
Screw the Wire Nuts on the Wires
With your pliers, twist together wires of the same color. Red wires attach to red wires; white wires attach to white wires; black wires attach to black wires.
Twist the wires together, clockwise, with your pliers before twisting the wire nut onto them.
An alternate method that saves a little time is to lay the two wires next to each other, then twist the wire nut onto the wires, twisting them together in the process.
For metal electrical boxes, run a third ground wire (bare wire) alongside the two ground wires that pass through the box, then secure those three wires with a wire nut. The loose end of that third wire is then attached to the inside of the metal electrical box using a screw.
Screw the Box and Cover in Place
The junction box will have holes inside to allow you to screw it onto a joist, rafter, or other sturdy wood section of your house. Adding an extender to your cordless drill bit will help you push the drill bit deeper into the box without disturbing the wires. Attach the cover securely to the box. Cover plates typically have a matte surface that allows them to be painted.