Different Types of Joints and Splices With Pictures
JOINING WIRES; Electric Cords Connected by Splicing, Soldering and Wrapping With Tape
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February 2, 1964
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WHEN two electric wires are joined together, the joint formed is normally called a splice. A good splice should not only be mechanically secure, it inust also form an electrical connection which is just as efficient a conductor as the wire itself.
Depending on the techniques used in twisting or tying the wires together, there are three tes of splices commonly used in household wiring and repair jobs: the pigtail splice the Western Union splice, and the tap splice (also called a branch splice).
The pigtail splice is most often used when wires are joined inside an electrical outlet box, or inside a junction bo where wires come together in an electrical appliance. It is the quickest and easiest of all splices to make, but it is never used where there may be stress or strain put on the connection later on.
The Western Union splice is used wherever two lengths of wire are to be joined end‐to‐end. and it is particularly designed for those jobs where there is a likelihood of strain or pull being applied to the wires after the joint had been made. It is aiso ine correct splice to be used when lengthening extension cords, lamp cords and other appliance cords by adding a piece to one end.
The tap or branch splice is used whenever a second wire must be connected at right angles, or when a wire must be tapped into a continuous main wire. This type of splice is not to be used where a considerable amount of stress or strain will be applied to the tapped wire though its strength will be considerably increased if the splice is soldered when complete (as described later on).
To make good electrical contact at the splice, wires must first be stripped of insulant on to expose the bare metal on the inside. For most splices, anywhere from one to three inches of wire will have to be bared. An ordinary sharp knife will prove to be the handiest tool for this job, but care shouid de exercised to avoid nicking or cutting into the metal wire when stripping off the insulation. The best way to avoid this danger is to remove the insulation by cutting at an angle with the knife — much like a pencil is sharpened. Cutting into the insulation at right angles to the wire increases the danger of nicking, and may eventually result in causing a break at this point.
After the insulation has been stripped off, the bare metal should be scraped or sanded until it is bright and clean. Dirt or oxidation will interfere With a good electrical connection, and even a slight film will also make it extremely difficult to solder the joint later on.
After the bared wires have been scraped clean, the appropriate splice is completed by wrapping the wires together as indicated in the drawings above. On small diameter wires, the splice can be made by simply wrapping tight with the fingers. However, on large diameter wires the first turn can be made with the fingers but the splice will then have to be completed by twisting tightly with a pair of pliers. Note that two methods are illustrated for making the branch or tap splice—one which is to be used when working with solid wire, and the other when working with stranded wires.
When splicing lamp cords, extension cords and other twoconductor wires, cut them so that the individual splices wilnot fail directly opposite each other. Making two spliced joints so that they are directly alongside each other increases the danger of an accidental short later on. In addition, when the completed joint is wrapped with insulating tape later on there will be an unsightly bulge or lump in the cord at this point. By cutting opposite ends a few inches shorter than one another, splices can be arranged so they overlap rather than being lined up directly opposite each other.
For a really permanent splice which will be just as strong and efficient as the original wire—and for every permanent splice there is a good chance of stress being applied later on—the completed joint should be soldered before wrapping with tape. Soldering can be accomplished with the use of a small electric soldering iron, or with a soldering copper which is heated separately with a blowtorch.
To prevent future corrosion, a rosin core solder, or a solder in combination with a non‐acid flux, should be used. Apply the iron to the joint so that the joint itself becomes hot enough to melt the solder. A poor joint results if the soldering iron is touched directly to the solder to melt it. When this happens, the solder will form a weak crystalline coating over the surface and it will not form the permanent bond required.
After soldering, joints must be wrapped with insulating tape to cover the bare wire and prevent shorts. There are two tapinb methots currently recommended. The older method calls for the use of a first layer of rubber tape, covered by a second layer of friction tape. The newer method uses only a single layer of a modern plastic elec trical tape. These have a very high insulating value, so only a single layer is required to adequately protect against shorting.
In either case, the tape should be wrapped on spirally from one end of the joint to the other so that succeeding turns overlap each other. The usual procedure is to start and finish on the tapered end of the insulation on either side.
For rapid joining and covering of the pigtail splices which are so often used in household wiring, most electricians prefer to use the plastic solderless connectors which resemble an oversized thimble in appearance. Commonly called wire nuts, these have a funnel ‐ shaped spring insert on the inside. The wires to be joined are pushed into this, after which the connector is twisted tight to form the connection. Since all exposed wires are enclosed inside this plastic shell, no additional taping or wrapping is required. Another advantage of this type of solderless connector is that, should rewiring be required later on, the joint can be easily opened and closed again without need for cutting or soldering.
Different Types of Joints and Splices With Pictures
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