Four-Way Switch

A four-way switch has two sets of traveler wires running between it and a pair of threeway switches. There is no common wire nor is there a common terminal. The continuity test for a four-way switch requires a few extra steps. You need to put the clip on any pair of traveler screw terminals separately and then touch each of the other screws with the probe. This is a total of six tests for each position of the toggle (see the following figures). The test should show two continuous currents for each position of the toggle switch. (The paths between specific traveler screw terminals vary with different manufacturers.)

A four-way switch box has two cables with three conductors coming into it (thus four hot conductors or wires). Two are black; the other two are a second color, most likely red. When you replace the switch, be sure to match the wires to the correct traveler terminals. New four-way switches either match their terminals up by color (two are brass and two are copper), or the back of the switch might have wiring instructions. This makes your job easier. You simply have to match one color of wire insulation to one set of screws (red wires to brass screws, for example). See the following figures for a typical installation.

Three-Way Switch

Replacing a three-way switch is more involved than replacing a single-pole variety. Now you have traveler wires to deal with (these connect the two three-way switches) as well as the common wires.
This means the cable running between the switches is 12/3 (or 14/3) cable rather than the more common 12/2 (or 14/2).
Follow the same safety and testing procedures that you would with a single-pole switch. Because three way switches (and four-way switches) are more expensive than a common single-pole switch, you want to be certain that the switch is really broken before throwing it away and replacing it. When removing a three-way switch from its box, note to which terminal screws or
back-wired slots the wires are connected. Mark the common wire with a small piece of masking tape, or attach each wire to the new switch as you remove them from the old switch. The common terminal screw usually is copper; the traveler terminals are brass or sometimes silver. Note whether the neutral wire is being used as a hot conductor.

New Switches

The easiest switch to replace is the single-pole switch. Before popping in a new one—and this is true with any device—read the specifications on the old switch. These usually are listed on the metal mounting strap and include the following:

• The amperage and voltage ratings
• The type of current it will carry (AC only for house current)
• The type of wire that’s compatible with the device (CU for copper only, CO/ALR for copper or aluminum, ALR for aluminum only)
• Its Underwriters Laboratory or other testing service listing

The back of the device will indicate the acceptable wire gauge and a stripping gauge for measuring the amount of insulation to be removed prior to installation. The location of your switch will determine how its replacement gets wired. A switch can be at either the middle or the end of a run (one complete circuit). These positions in the run are simply defined:

• A middle-of-the-run switch can be anywhere between the beginning and the end of the circuit. There will be at least two cables entering the box (at a minimum, one on the line side coming from the panel and one leading to a fixture or other device).
• In an end-of-the-run switch (also referred to as a “switch loop”), the cable runs from the fixture to the switch. This requires special treatment of the white wire.

Remember to shut the power off at the service panel or fuse box and to test the switch with a voltage tester before removing the wires. Note the condition of the ends of the wires. You don’t want to reuse damaged or nicked wires. If you find any damage, cut off the minimum amount of wire necessary to remove this section and then strip off sufficient insulation (about 5/8 of an inch) so the wire will make a solid contact.