Wire splicing is a standard electrical procedure that allows you to extend wires and add devices, while often reducing drywall demolition and repair.

Wire splicing can be done inside a standard fixture box, such as an outlet or ceiling light box. Wire splicing can also be done outside a standard fixture box. The cable connections are made inside a junction box that is installed expressly for the purpose of splicing. The box has a blank cover that can be accessed whenever you need to work on the wires.

When to Splice Wires

Many electrical projects require you to join (splice) circuit wires together. Wherever possible, the best method is to run a solid, uninterrupted cable from the service panel to the device or from device to device. This is preferable in many ways: it reduces the possibility of severed wires in an emergency, provides a smoother wall or ceiling surface, and eliminates confusion.

But this is not always possible, and this is where wire splicing comes into play. Learning how to splice wires makes it possible to tackle countless projects that enhance your living space.

• Moving an outlet
• Moving a light fixture
• Removing a wall
• Finishing a basement
• Dealing with loose wires
• Bringing improperly connected wires up to code
• Branching a circuit into two or more directions
• Leaving a junction box in place for future devices

Type of Materials to Use

Junction Box

Junction boxes come in both plastic and metal varieties. Some electricians prefer the durability of metal boxes, but if you use a metal junction box, remember that it will need to be connected to the ground system with a grounding pigtail wire.

One end of the pigtail is grouped together with the circuit grounding wires, while the other end is screwed directly to the metal box.

Plastic junction boxes may also be acceptable. Do-it-yourselfers often prefer plastic boxes because they are lighter weight, have softer edges, and the punch-outs are easier to remove. No grounding pigtail is required with plastic junction boxes.

Wire Connectors

The method demonstrated here is the correct way to splice electrical wires using UL-approved wire connectors joined inside an approved electrical box.

These connectors can be the familiar twist-on wire nuts or newer-style push-fit connectors. This is the method approved by the National Electrical Code (NEC). Either wire nuts or push-fit connectors are acceptable, as long as there is sufficient space in the box to contain them.

The old, informal method of splicing wires with electrical tape should never be used. Splicing wires with electrical tape creates a bond that is less solid than with wire nuts or push-fit connectors. Do not splice wires with electrical tape.¹

While you should not splice wires with electrical tape, tape is often used to bind wire nuts to the wires.

Safety Considerations

Making wire splices is not a difficult technique. But like any electrical repair that involves handling circuit wires, DIYers should have a good understanding of electrical systems as well as some experience with basic electrical repairs.

Any project that involves working with circuit wires requires that you first turn off the power to the circuit at the service panel (breaker box).

Electrical splices can never be left on their own in a wall or ceiling cavity. Instead, all splices must be contained within an approved junction box or fixture electrical box. 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.

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What You’ll Need

Equipment / Tools

• Cable ripper
• Wire stripper
• Hammer
• Screwdriver
• Pliers
• Cordless drill with driver bit
• Drill bit extender (if needed)

Materials

• 1 metal junction box with cover
• 2 cable clamps for box
• UL-approved wire connectors
• Wood screws for mounting box
• Grounding pigtail wire

Instructions

How to Splice Electrical Circuit Wires

The project shown here assumes that the wall surfaces are open to provide access and that the electrical cables have already been run inside the wall cavities. If not, the process of fishing cables will make the project more complicated and time-consuming.

1. Examine WiringMake sure that you are joining two similar cables. The cables must match in terms of wire gauge and the number of individual conductors in the cable. Modern wiring (up to 50 years old or so) will have the gauge and number of wires printed on the outer sheathing of the cable. For example, a cable labeled “12/2 w ground” contains two 12-gauge insulated conductors plus a bare copper grounding wire.
2. Remove Outer Sheathing From CableExpose the individual conducting wires within the tough outer plastic jacket by using a cable ripper to slice through the sheathing. Do not use a utility knife, as you risk cutting into the individual wires. Insert the cable into the hole on the cable ripper until it is about 6 inches from the end of the cable. Lightly press the sides of the ripper together and draw the tool off the end of the cable to slice through the sheathing.Trim away the severed portion of the sheathing and paper filler with the cutting jaws on a wire stripper or with a utility knife.
3. Strip Insulation From ConductorsEvery conducting wire in the cable, except for the ground wire, will be coated with color-coded plastic insulation. Use a wire stripper to remove about 1/2 inch of this insulation from each wire. The stripper tool has slots to match various wire gauges; use the slot that matches the wires in your cable.
4. Inspect the CablesCheck the wiring on both cables for any sign of damage, such as cut, chewed, or burned insulation or nicked wiring. When the cable sheathing and wire insulation are properly prepared, about 6 inches of wire should protrude beyond the edge of the remaining sheathing, and individual wires should be stripped back and smooth, not nicked.
5. Remove Knockouts From Junction BoxWith a screwdriver and hammer, loosen two opposing knockout disks from the junction box. Use pliers to pry off and completely remove the discs. Often, you have to rock the disk back and forth several times before it will come free. Dispose of the disks.
6. Attach Cable Clamps to the Junction BoxPlastic cable clamps usually just snap into the knockout openings in the box. For metal cable clamps, first remove the threaded tightening ring, then insert the clamp through the knockout opening. Screw the tightening ring back onto the clamp from inside of the box, and use pliers to tighten the ring securely. Do not turn too hard or you may break the clamp.
7. Insert the CablesInsert one cable into each junction box knockout, 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. The cable sheathing should extend past the clamp into the box by 1/4 to 1/2 inch. Plastic cable clamps usually have a tab that you force closed in order to grip the cable. With metal clamps, tighten the screws on the clamp until the cable is securely gripped.
8. Attach the Box and Cover PlateThe junction box has holes in the back and sides to allow you to screw it to a wood framing member. If necessary, you can attach a bit extender to a drill to help you drive screws without disturbing the wires. Make sure the box is securely attached to the framing member at a depth that will allow the cover plate to fit securely over the box once the finished wall or ceiling surface is in place. For example, if the wall will be finished with 1/2-inch drywall, then the front edge of the box should extend 1/2 inch beyond the front face of the stud. This will ensure that the box will be flush with the finished wall surface.
9. Make the Wire ConnectionsUsing approved wire connectors, join together the conducting wires with similar insulation colors.With standard wire nuts, some electricians prefer to twist the wires together first with pliers, then screw the wire nuts over the ends of the wires. However, some wire nut manufacturers instruct to simply hold the two parallel wires together, then twist the wire nut over the bare ends of the wires in a clockwise direction. However you do it, the wires should be connected securely enough that they don’t come free from the wire nut when you tug on them. There should be no bare wire exposed at the bottom of the wire nut. Some electricians like to wrap a loop or two of electrician’s tape around the base of the wire nut and wires to help reinforce the wire connection.Another type of approved wire connector is the push-fit connector. With these connectors, you simply push the bare end of the wire into a grip-fit socket on the connector.The bare copper circuit grounding wires should also be joined together in the box, using an approved connector. For metal electrical boxes, run a third grounding pigtail (bare copper or green insulated) to the two bare copper circuit grounding wires, using a wire connector. The free end of the pigtail is then connected to a threaded screw opening on the metal box, using a green grounding screw. This technique grounds the electrical box and improves the safety of the circuit.After completing the connections and finishing the wall or ceiling surface around the box, attach the cover plate securely. Some cover plates have a matte surface that allows them to be painted.

How to Run Electrical Wire Through Walls

FAQ

• What is the safest way to join electrical wire?The safest way to join electrical wire is detailed above using approved electrical boxes and connectors. The most critical step regarding safety is turning off power to the circuit at the service panel in the breaker box first. When in doubt, hire an electrician, which would truly be the safest way to join electrical wire.
• How many times can you splice electrical wire?There is no standard answer to how many times you can splice electrical wire. It depends on the quality of the wire and your DIY skills. That said, many suggest not to splice electrical wire more than three times.
• When is it against code to splice wires?It is against code to splice wires that are not contained in a junction box.
• When should you hire a professional when splicing wires?You should hire a professional to splice wires if you aren’t confident in your personal electrician skills. Even if you are knowledgable on the topic, if the wires have already been spliced a couple of times, you should consider hiring a professional.