Whether you’re adding an outdoor light to your home, installing a new outlet in your kitchen, or repairing a failed circuit breaker, you may need to connect wires. But doing so safely and properly is important, because a wiring mistake can cause short circuits or shocks, and even fires.
Mistake: No electrical box | Never connect wires outside of an electrical box, which is also called a junction box. These boxes protect connections from accidental damage and contain sparks and heat caused by a loose connection or short circuit.
They’re also helpful for splicing wires together, because they provide a safe place for these connections to be made. In addition, they make it easier to locate the wiring splice area when you need to connect cables to switches or other devices.
You should also check your wiring carefully for stranded or mismatched wires, which are common and cause trouble. If you have mismatched wires, cut them off and strip their insulation back to the copper conductor, using a wire stripper tool (see “Wire Stripping”).
To connect the hot, neutral, and ground wires in a box, follow these steps:
Remove the switch cover by unscrewing its two or four screws and inserting a screwdriver through the knockout on the side of the box. Alternatively, use a hammer to punch the knockout out.
Next, pull each individual hot or neutral wire out of the box and strip off about a half-inch of plastic insulation from its end, using a wire stripper tool. You should then have about 6 inches of exposed wire beyond the sheathing on each end, and each individual wire should be smooth and free of nicks and cuts.
Once you’ve stripped off all the plastic insulation, route each individual wire along the back of the switch box to a central location and cut it to length. Repeat for each cable in the box, exposing about 3/4-inch to 1-in. of copper conductor on each wire.
After cutting each wire, twist the conductors tightly together with pliers, and cap them with a wire nut. Carefully fold the bundle so that it lies flat in the box.
Wire splicing is a time-consuming process, but it’s often necessary when replacing a worn out flex or a thermal fuse. You’ll need to use a connector that’s designed for splicing. If you’re not sure which type to purchase, consult the package.
Typically, you’ll need to use a special green wire nut to join the grounding wires together, and a pigtail–a 6-inch length of the same type of ground wire–to attach the ground screw in the box. If the box is metal, you’ll need to wrap the ground wire around the screw in the same direction that the screw tightens.
In some cases, the best way to splice is to simply twist the wires together, then dip the twisted ends in molten solder and twist them together. This method is usually the simplest and most reliable. But it can be difficult to do when you’re splicing stranded or mismatched wires, so it’s best to try other methods first.