In the average home, most switches are of the single-pole type—an on/off toggle controls a light or outlet from a single location.
The basic structure of single-pole light switches is this: There are two same-colored terminals, usually brass or silver, for the circuit’s “hot” wire connections, and there is a green grounding screw that is attached to the circuit’s bare or green ground wire. (Up until a few years ago, many light switches did not have grounding screws because their plastic toggles were considered to be shockproof, but all modern switches have them for added safety.) Some switches utilize screw terminals; others have terminal holes that you can push the stripped wire ends into. You may use copper or aluminum wire for switches marked with the symbol “AL-CU,” but unmarked receptacles, and those that have the “AL” symbol with a slash through it, can only use copper wire.
Here is how to replace or install a single-pole light switch:
1) First, shut off the power to the circuit—never work on an energized circuit. If you’re replacing an existing switch, use a screwdriver to remove the plastic faceplate and to unscrew the existing switch from the electrical box. Use an electrical tester to check the wires that go to the existing switch (or the new wires that are intended for the switch) so you can be sure they are not active. Place one probe on the bare ground wire inside the box and touch the other probe on each of the wired screw terminals of the switch or the bare end of the black wire that will carry electricity to the switch. No voltage should register. Once you’re sure the power is off to the switch, use the screwdriver to remove the existing switch (if there is one) from its wires.
2) Straighten the ends of the circuit wires you will be connecting to the switch, and then use wire strippers to remove 1/2-inch of insulation from the wire ends.3) Secure the circuit’s bare or green grounding wire to the green grounding screw on the switch. If the switch has its own grounding wire, twist the bare end together with the circuit’s grounding wire, using lineman pliers, and secure it with a copper compression sleeve or wire nut. Note: If you are using a metal box, include a grounding jumper from the ground wire connections to the box.
4) Connect the two black wires (sometimes called “hot” wires) to the switch’s screw terminals. It does not matter which wire goes to which terminal. Note: Some switches have holes in the back of the switch for the wires, which you can use instead of the terminal screws on the side.
5) Mount the switch (be sure it’s right side up). First, fold the wires behind the switch and carefully push the switch into the box. Next, align the switch vertically by adjusting the screws in the mounting slots. Also make sure the switch is flush with the wall. If it isn’t, shim it out using the break-off portions of the switch’s plaster ears or use special washers sold for shimming purposes. Screw the switch to the box.
6) Screw the faceplate to the switch using the screws included with the faceplate.
In addition to wiring a switch of the single-pole type, you can wire three-way switches that allow you to turn the light on and off at two different locations, such as at either end of a hallway or stairwell. It is also possible to wire a four-way switch that allows you to control a light from three locations. Just remember the cardinal rule when working with electricity: Make sure the power is turned off to the area you are working on.
