Glenda Taylor | posted April 30, 2021 3:29 PM

In a standard single-pole switch, one light switch controls one light fixture-on/off. Things get a little tricky when wiring with a 3-way switch, which has two switches and one light. But when you understand how current is transmitted in this circuit, everything becomes meaningful.

Although installing new wires is almost always done by a licensed electrician, DIYers can usually successfully replace old switches with new ones if local regulations allow it. Replacing a 3-way switch is a simple task, but it is more complicated than replacing a single-pole switch. Anyone preparing to replace a 3-way switch should have working knowledge of switch wiring. If you are not used to changing switches, call an electrician.

When carrying out any wiring, safety is always the primary consideration. The power must be turned off at the circuit breaker box, and the wires in the switch box should be tested with a voltage tester to ensure that they do not get hot before proceeding.

Going home late at night, staggering to the other side of the dark room to look for the light switch, this is not a pleasant thing. This is the convenience of three-way switches-they allow users to turn on the central lights from different sides of the room or the upper and lower ends of the stairs. The 3-way switch setting can even be used with the dimmer switch, as long as the dimmer switch is designed for 3-way wiring.

A single 3-way switch is similar to a single-pole switch. However, they are not marked as "OFF" or "ON" because they allow or stop current according to another switch position in the settings. Essentially, the three-way switch is a toggle switch.

Two different types of cables are used for the wiring of standard 3-way switches, the most common are 14/2 cable and 14/3 cable. 14 represents the wire size (rated for 15 amp circuits), and the number 2 or 3 below represents the number of wires in the cable. The number of wires in different cables is important because an extra wire is required in one part of the 3-way switch setting. If there is no 14/3 wire, it is impossible to let two switches control the light.

Some households may use the 12th line instead of the 14th line, which only means that the line can carry more amperes. 12 specifications can carry 20 amps. Houses built since the mid-1960s may contain non-metallic sheathed cables (NM), commonly referred to as Romex, named after the popular wire brand.

The 14/2 NM cable contains two wires: one black and one white. It also contains a third bare copper wire. In the typical 3-way setup described here, the cable is connected from the power supply to the first switch box, but other wiring configurations are also possible (see below). The following wire colors are standard, but different wire brands can use different colors of wires.

The 14/3 NM cable consists of a bare copper wire and three wires: one black, one white, and one red. In a typical 3-way setup, the 14/3 cable runs from the first switch box to the second switch box.

The standard 3-way switch has four terminals, and each terminal is represented by a colored screw. The screw position of each switch is usually similar. Some manufacturers locate screw terminals in different locations, so be sure to study the diagram that comes with the switch.

In a typical 3-way switch, the white neutral wire is not connected to the actual switch. Instead, they are connected to each other. This creates an uninterrupted return circuit for the power supply, which is usually the bus terminal on the circuit breaker panel.

The neutral wire can be connected by twisting two wires together in each switch box, but today's lever nut connectors make it simpler. Wire connectors (such as Aigreat's lever nut connectors) work by lifting the lever, inserting the end of the wire, and then pushing the lever down to lock the wire in place.

To make the 3-way switch setting work, power must be supplied through a traveler or another wire, and the route depends on whether the toggle switch is in the up or down position.

When the first switch turns on the light, current will flow through one of the wires. However, if the second switch is used to turn off the light, when the first switch turns on the light, current will flow through the other wire. Think about how a conductor can switch a moving train from one track to another—this is how the three-way switch transmits power along the red or black travel wires so that both switches can control the lights.

Although the above wiring configuration is typical, it is not the only way to connect a 3-way switch. The configuration depends on where the power enters the circuit (at the switch or at the lamp). Alternate wiring configuration can only be done by an electrician.

If the DIYer opens a switch box and finds a white wire with black tape-the white wire is hot. This does not mean that a professional is required to replace a switch, because replacing a 3-way switch does not require laying new wires—just disconnect one switch and connect the new switch.

Regardless of the wiring configuration, the easiest way to successfully replace an old 3-way switch with a new 3-way switch is to mark each wire with its connected terminal before removing the wire from the old switch. Then, connecting the correct wires to the correct terminals of the new switch is a simple process.

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