While doing almost any kind of electrical wiring in your home, you'll likely run into wire connectors. These little plastic caps, often called wire nuts, twist over the bare ends of wires to make a tight connection that is also reversible, in case you need to replace the device in the future.
Wire Connectors Are the Best Connectors
If you ever find wires joined with electrical tape, or the wires are twisted together and then wrapped with electrical tape, get rid of the tape and join the wires with wire nuts. Never use tape in place of wire nuts. It's simply not secure enough, and it's vulnerable to damage. Some people like to use wire nuts and wrap them with tape. This fine to do, but you probably won't find any wire nut manufacturers advising you to do it.
Wire Nut Types
Standard wire nuts are roughly conical in shape and usually have ridges on their sides so your fingers can get a good grip. Some types have little side wings instead of ridges. Inside the plastic cone is a little square-cut spring that provides tension on the wires to hold them securely. As you tighten the wire connector, the spring draws tighter around the wires. Variations on classic wire nuts include push-in wire connectors (you push the straight wire ends into holes), waterproof wire connectors (usually gel-filled to keep out moisture), and butt-splice connectors (for joining wires end to end).
How to Use Wire Nuts
Always follow the manufacturer's instructions, as techniques vary by product. But here's the standard procedure: Strip about 1/2" to 3/4" of insulation from the end of each wire, using a wire stripper. Be sure to use the right hole in the stripper so that you don't cut into the metal of the wire. Hold the wires together so their ends are aligned. Fit the appropriate size of wire nut over the wire ends and push into the wires while twisting the nut clockwise. Twist until the nut is as tight as you can get it and there is no bare wire showing below the nut. You can also give the nut a final short twist with a pair of linesman pliers if you feel the nut isn't tight enough. Give each wire a little tug to make sure it is securely held by the nut. If a wire pulls out at all, remove the nut and start over.
Some people, including many electricians, like to twist the wires with lineman pliers in a clockwise direction before applying the wire connector. They feel that it makes for a more secure connection and may help keep the wires together in situations where vibration can possibly work the nut loose. In any case, it's best to follow the manufacturer's directions.
Tip: When joining solid-copper and stranded-copper wires, strip the stranded wire about 1/8" more than the solid wires. The stranded tends to wrap around the solid when you twist on the nut, so the extra length helps make a strong connection. Before putting on the wire nut, align the wires so the edges of the insulation are even and the stranded wire ends extend past the ends of the solid.
Wire Nut Sizes
Wire connectors come in different sizes and colors. The color indicates the size, quantity, and type of wires the nut can accommodate. The wrong size of nut is either too large or too small for the wires. Either way, this means a weak connection, which is potentially dangerous (loose wires start fires). The packaging for all wire nuts includes a chart that tells you what color of nut to use with the wires you're connecting. For example, a gray nut may work for a minimum of two 22-gauge stranded wires up to a maximum of two 16-gauge solid wires. The next size up (say, a blue nut) may be suitable for two 22-gauge solid wires up to a maximum of three 16-gauge solid. Overlap in the sizing chart is common; just make sure you're within the range for the color you're using. Colors vary by manufacturer, so always consult the chart on the packaging.