How to Splice Electrical Circuit Wires

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When doing remodeling work, it may be necessary to splice wires to relocate circuits or add new devices. A splice is a mechanical connection between two wires so they can continue as one wire. A plastic connector called a wire nut is used to insulate and secure the splice.

Use a wire nut size appropriate for the number and gauge of the wires you're using. Wire splice connections must be spliced inside a covered electrical box, known as a junction box. A junction box is usually square and made of metal. When installed, the junction box must not be concealed inside walls or ceilings, so it remains accessible at all times. Keep on reading to understand how to splice electric circuit wires:

Safety Precautions for Splicing Electrical Wires

Before starting any work to connect electrical wires, turn off the circuit breaker supplying electricity to the wire, you want to splice. Use extreme caution when working with electricity, as it can cause serious injury or even death when not handled properly. It’s important to calculate safe electric load capacities so you always stay out of danger.

Safety Precautions for Splicing Electrical Wires
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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 junction box provides a safe environment for your splices, protecting them against impact and having sparks and fire if anything should go wrong.

While junction boxes may seem unwieldy and unnecessary at first, you'll find that they're easy to work with and will make your work safer. Another precaution you should consider is never working on electrical wiring alone, find a partner to help you. Also, never work on electrical wiring in wet or damp conditions. Make sure you wear rubber-soled shoes to insulate your body.

What You'll Need

  • Cable ripper
  • Wire stripper
  • Hammer
  • Screwdrivers
  • Pliers
  • Cordless drill with a driver bit
  • Drill bit Extender
  • Cable clamps for box
  • Grounding pigtail wire
  • Wood screws for mounting box
  • UL approved wire connectors
  • Metal junction box with cover

Here is the step-by-step guide on how to splice electrical circuit wires.

Remove Outer Sheathing from Cable

Make sure that you're joining two similar cables. The cables must match in terms of wire gauge and the number of individual conductors in the cable. Modern wiring will have the gauge and number of wires printed on the cable's outer sheathing. For example, the cable labeled 12/2 w ground contains 12-gauge insulated conductors plus a bare copper grounding wire.

Begin by exposing the individual conducting wires within the tough outer plastic jacket using a cable ripper to slice through the sheathing. Do not use a utility knife, as you risk cutting into individual wires. Insert the cable into the hole on the cable ripper until it's 6 inches from the end of the cable.

Strip Insulation from Conductors

Once the wire is exposed, grasp the sheathing with one hand and push down on it while holding a wire stripper in your other hand. This will force the cutting blade into the plastic insulation, allowing you to carefully slice through it without damaging individual wires beneath. Strip every grounding wire, except the ground wire, which will be coated with color coded plastic insulation.

Strip Insulation from Conductors
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Inspect the Cables

It is extremely important that you inspect each wire after it's been stripped. Damaged insulation could expose the wire to environmental damage, which will cause a short circuit later. 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.

Remove Knockouts from Junction Boxes

If you are using an existing junction box, the knockouts for individual circuit wires must be removed. If you are installing a new junction box, it should come with knockouts to connect to each wire beneath the sheathing. Using a hammer and a screwdriver, loosen two opposing knockout disks from the junction box. Use pliers to pry off and completely remove the discs.

Remove Knockouts from Junction Boxes
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Attach Cable Clamps to the Junction Box

For plastic cable clamps, snap them into the knockout openings in the box. Remove the threaded tightening ring for metal cable clamps, then insert the clamp through the knockout opening. Screw the tightening ring back onto the clamp from inside the box, and use pliers to tighten the ring securely. Do not turn too hard, or you may break the clamp.

Insert the Cables

Insert one cable into each junction box knockout through the clamp. Make sure 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 a 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.

Attach the Box and Cover Plate

Attach the mounting strap to the knockout in the junction box with a screw. Tighten, secure, but do not overtighten and damage the cable or clamp.

Mount the electrical box on the wall at about eye level using screws provided or by using your drywall anchors and screws. Place the faceplate over the cable and metal clamp. Tighten the screws on the plate's mounting ears, if your box didn't come with them already attached to the faceplate.

Make the Wire Connections

Using approved wire connectors, join 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 end of the wires.

In addition, 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 do not 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. Using a wire connector for metal electrical boxes, run a third grounding pigtail, bare copper or green insulated to the two bare copper circuit grounding wires.

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, attach the cover plate securely. Some cover plates have a matte surface that allows them to be painted.

FAQs on How to Splice Electrical Circuit Wires

Can you splice wires without a junction box?

No, all splices must be in a junction box, and the junction box must be accessible.

Can you splice wires behind drywall?

The splices must be contained within an approved junction box or fixture electrical box. The box must remain accessible and cannot be hidden behind drywall or other building materials that would require removal to get to the box.

What are the benefits of splicing electrical circuits at home?

As long as you have the knowledge of electricity, you can splice your electrical circuit wires at home, hence saving on the electrical project costs.

Final Thought on How to Splice Electrical Circuit Wires

As you can see, knowing how to splice wires can save you time and money on several electrical and lighting projects around your home. However, if you're apprehensive about working with electricity or lack basic electrical knowledge, do not hesitate to hire a licensed electrician for your project. 


Kristina Perrin

Kristina Perrin

Kristina is an expert DIY home remodeler and mom to three. When she's not cooking or experimenting with new recipes, you can find her working on new home improvement projects or writing about her favorite kitchen appliances or DIY projects on Kitchen Infinity blog.

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