Electrical Wire Splice Basics for Homeowners
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Safety Warning:

Do not attempt to work on your electrical wiring, switches, or outlets unless you are properly trained and equipped to do so. Electrical components in a building can easily cause an electrical shock, burn, or even death.

Even when a hot line switch is off, one terminal on the switch is still connected to the power source. Before doing any work on the switch, the power source must be turned off by set­ting a circuit breaker to OFF or removing a fuse. See SAFETY FOR ELECTRICAL INSPECTORS and Electrical Wiring Books & Guides

Splicing electrical wires is a task that can be learned easily, but if the splice is not made correctly, the electrical system will be unreliable and unsafe, risking fire or shock hazards.

Our photo at left shows some pigtail splices inside of a metal junction box - in this case, because the wires are aluminum, the connectors shown are not the proper ones, and these splices are a fire hazard. We introduce the proper connectors used for aluminum wire below. This photo shows how electrical connections can burn up if you use the wrong device or do not make the connection properly.

The proper way of making safe, secure splices is to make a good mechanical and electrical joint-that is, strong enough not to pull apart and tight enough so there is no loss of voltage. As this is tricky work, a continuous run of new wire is always better than any splice.

Splices in electrical wire that carries electrical current in a building (such as for lights or electrical outlets) must be completed using an approved mechanical connector and must be enclosed in an approved junction box which itself is secured to the structure.

In addition, the NEC and other electrical codes specify lots of precise details describing the number of wires of various sizes that can be enclosed in junction boxes of various sizes, where these boxes must be located, how they can be covered, etc.

Our photo at left shows an improper and certainly not code-compliant mess of pigtail splices in electrical wires. Courtesy of Tim Hemm.

Electrical wires that connect appliances, lamps, stereo equipment, etc to wall outlets should never be spliced for permanent use, but occasionally, it may be necessary to splice these wires when repairing or modifying appliances or for emergency repairs.

Our photo shows an improper, unsafe, and certainly not code-compliant splice in lamp cord used to wire a wall-mounted light fixture. Exposed electrical connections like this are a fire and shock hazard.

Further, this is an un-approved use of lamp cord or "zip cord" to replace what should have been approved electrical wire, a junction box, etc. When we see exposed electrical work like this we know that someone un-trained has been doing electrical work on the building and we need to be alert for other faulty electrical wiring practices.

Our our enlargement at left and our page top photo shows a pigtail splice at the lower left of the drawing.

Strip off at about 1 an inch of insulation from the end of each wire.

When you are joining electrical wires used to carry current in a home you'll be using a solderless twist-on connector such as we show at left. In this case the length of wire from which you need to strip insulation depends on the number of wires being joined together and the size of the twist-on connector you're going to use.

In good practice you don't want to strip off too much insulation - when the splice has been completed and the twist-on connector has been installed, you should not see any bare wire exposed extending beneath the bottom edge of the mechanical connector.

If you are stripping wires that are not part of the building's electrical system, such as speaker wires, you may not be using a mechanical connector, just tape, and the length of wire that you need to strip depends on the number of wires being joined and your ability to twist them securely together.

Don't damage the wire during stripping of insulation: Be careful that you don't nick the metal wire when cutting the insulation in preparation to strip it off.

If you do nick the wire, as shown in Carson Dunlop's sketch at left, the risk is that the nicked end will later break off, destroying your connection, and perhaps also becoming unsafe.

If you have nicked the wire by accident, cut the nicked portion of the wire end off and start over again.

Splices in an building's electrical circuit must be connected using an approved wiring connector, such as a twist-on connector ("Wire Nut" is a trademarked name for a brand of twist-on connectors.)

Twist-on connectors come in different color-coded sizes, and you must choose the proper twist-on connector, depending on the thickness (gauge) of the wire and the number of wires you're combining in your splice.

The connector is placed over the end of your twisted splice, pressed onto the wires, and turned clockwise until it is tight.

Be careful when pushing an electrical splice back into the junction box - don't loosen the connector you've installed or your connection will be poor and possibly unsafe.

Using the wrong type of electrical splice connector, or one for which studies have shown poor performance, can lead to a melted or failed electrical connection, possibly risking shock or fire.

Our photo at left shows an expert using a Scotchlok 3M electrical connector to cap a splice which was also coated with an antioxidant. We discuss this connector (now obsolete for aluminum wire repair) in more detail at How to Reduce the Risk of Aluminum Wiring.

Electrical wires in a building are sometimes joined without twisting wires together. Instead we use special approved connectors.

The AlumiConn ^TM connector shown here is used to splice a copper "pigtail" wire together with one or two aluminum wires as a step in reducing the fire hazard associated with aluminum electrical wiring.

This connector performs well provided that the wires are properly secured in the connector. We discuss this connector in more detail at How to Reduce the Risk of Aluminum Wiring.

The AMP COPALUM connector (now sold by TYCO) is also used to connect copper to aluminum wiring, and is also discussed at How to Reduce the Risk of Aluminum Wiring.

This connector must be installed by a an expert trained in aluminum wire repair and using a special crimping tool which forms a cold weld between the metals.

The Wago Wall Nut is a device which connects several wires of different gauges and types, as you can see in this photo.

Sometimes it is desirable to join one wire to another at some midpoint without cutting the second conductor. The tap splice can be used in this case. What characterizes a tap splice is that one wires to be joined is not cut, but rather is kept continuous.

Remove insulation from about two inches of the continuous run wire.

Wrap the joining wire tightly around the continuous wire. Solder and tape the spliced wires.

A tap splice is shown in our page top sketch at lower right and again here. If the joining wire is stranded, such as speaker wire, the strands may be separated into two bunches and then wrapped in opposite directions along the continuous wire to form a more secure connection.

Tap splices are not used in home electrical circuit wiring except for older knob-and-tube electrical wiring.

Our sketch at left, courtesy of Carson Dunlop, shows the usual ways that knob and tube electrical wiring is connected in homes.

Knob and tube wiring connections were made outside of electrical junction boxes. In normal practice knob and tube wiring splices are soldered and also taped.

We do not use plastic electrical tape on these installations, but rather the heavier cloth-based black electrical tape.

Review our discussion below to see when you can just tape electrical wire splices.

In some jurisdictions (especially in the U.S.) knob and tube electrical wiring was code-approved and used into the 1970's or later.

In most jurisdictions there is no requirement that knob and tube wiring be removed or replaced, but it is not permitted to extend a knob and tube electrical circuit - say by adding wires to connect additional devices like receptacles.

If the knob and tube wiring system is not in good repair it may need to be replaced for fire safety.

In a jurisdiction where it is permitted to extend a knob and tube electrical circuit, it's necessary to change from open soldered and tape-wrapped electrical wire splices to splices contained in electrical junction boxes, as we show in Carson Dunlop's sketch.

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