How Does A 3 Way Switch Work

by Linea Lorenzo

In most cases, we control our lights from one light switch. This is the most common scenario in most homes. When the control of light is done from two different light switches, it is no longer one light switch. It is referred to as three-way- light. For the switches, they are called 3 way- light switches.

It gets more interesting when you try to understand how a 3-way switch works. Unless you are an electrician, it is a bit complicated. The idea of having a 3-way switch is the ability to control a single light from more than one location.

It is vital to have some knowledge on how a 3-way switch works. This is because if it is not wired correctly, you can’t diagnose the problem. In this article, we are going to discuss more on a 3-way switch.

Let’s dig deeper to have a clear picture of how stuff works.

How Does A 3 Way Switch Work
How Does A 3 Way Switch Work

For example, if you live in a big house, you need to switch your lights from different locations. You don’t need to move from one room to another looking for the switch to switch on/off. That means the switches will be installed in different places, but you can still switch on/off from wherever you are. The installation needs special wiring connections, and it is done in pairs.

When the toggles are up or down at the same time, the electric circuit is considered to be complete. That means the lights turn on. If they are opposite, the electrical circuit is cut on, and the lights turn off. The reason behind that is to give either of the switches a chance to control the on/off function.

How Do You Identify a 3-Way Switch?

You can identify them in two significant ways

  1. The switches have a single-pole switch. So on the switch toggle, you will not find the “On and Off” marking.
  2. The body of the switch always has a grounding screw which is green in colour. But you will find three other screw terminals that are mounted. The one with the dark color more than the rest is called the common. With light brass colors are the other two called the traveler terminals.

Let’s get acquitted to the parts of a 3-way switch. The information will help us understand more about how the switch works.

Power in: This is the cable that supplies power to the lighting system. When installing the lights, the power stops on the fuse box.

Cable: This is where one or more wires are bundled together. They are bundled in with insulating material. The insulation is done on each wire separately. Note the ground wire is left bare or insulated in green.

Neutral: It is the white wire that is found in power in cable. This cable does not connect to any switch. It is usually ended with a wire nut to enable it to connect to another neutral wire.

Two rope: Some cables have two individual wires and a ground wire. They are mostly called “two rope.” They are black and white with a green or copper ground.

Fuse box: This is a box that contains fuses or circuit breakers. It is a place where all the power is controlled from. You can either switch on or off from a fuse box.

Ground: This is the grounded wire found in each switch. It is colored in green or just left bare.

We now move to wiring. How is it done?

As we discussed earlier, wiring of a 3-way switch requires special wiring. It is not done like a single pole switch. If you might have forgotten we noted that it doesn’t have on and off on the toggle. No instructions labeled on the toggle to describe whether you are switching on or off. Neither does it have a up and down feature.

There are three significant ways that 3-way switches are wired in order to control more lights. The three methods are all good. The right one for you will entirely depend on where the light enters the circuit and where the switches and the lights are placed.

  • When the power-in cable gets in the light box 

It works better if the switches share the wall and the light fixtures share a common breaker. In this case, the cables must be run straight to the light box, then between the 2 switches, and then from the light box to one of the switches.

Let’s see how the current goes up to the lighting fixture.

  1. Through the black wire, the current flows to the light box.
  2. The black wire is joined to a white wire in a “two-rope cable” which goes to the first switch box. The switch box is joined again to the white wire in a “three rope cable” and continues its journey to the second switch at the common terminal.
  3. When the switch is put up, the black it exits the switch. This happens on the right-hand traveler terminal. After that, it continues to the red wire at the back of the traveler terminal, which is on the first terminal.
  4. Still, the switch is up. It exits the switch, taken away to the terminal on the black wire in the two rope cable from the light switch.
  5. It goes down the black wire, and the electricity penetrates to the light box. After that, it proceeds to the light fixture.
  6. Later, the current goes into the light, it exits on the white wire, and then the neutral wire goes back to the power-in cable. Then it lights.
  • When the power-in gets in the light box but use 3 rope cables for individual switch box

The second method is applicable if the power is only on the ceiling and the switch boxes are not on the same wall. In that case, the power-in line penetrates to the light box, though 3 rope cables are put up between the light box and the individual switch box. It is presumed that it is easy running the cables in the ceiling rather than between the switches.

Let us follow the flow of the current to the light fixture

  1. The current goes to the light box on the hot wire
  2. It uses the white wire penetrate to the “common terminal” to the 1st switch
  3. The current then exits the switch from the “traveler terminal”.
  4. After that, the current goes back to the light box. Here it is joined to another wire. Later it travels to the traveler terminal on the 2nd switch.
  5. Through the 2nd switch, it gets out from the “common terminal.” It goes another time to the light box and proceeds to the light.
  6. Lastly, the neutral wire travels from the power-in cable straight to the light fixture.
  • Power is getting in to switch one.

At this particular wiring, the power is brought to the 1st switch via the 2nd switch and the light feature. For this particular method, it is applicable when you have multiple switches sharing the same box. In such a scenario, other switches should have the power to operate other lights. They should do that without the need to have different power in line to operate them.

NB; in this method, the white wire should be used. This is a requirement which states that neutral wires must be white. By use of the three rope, the power in must be taken to the light fixture.

  1. The flow of the current
  2. The current goes into the 1st switch behind the hot wire. It is connected to the common terminal.
  3. With a down position switch, the current goes out of the switch through the red wire. Through the traveler terminal, it enters to 2nd switch.
  4. Still, the switch is down, the current gets out from it on the black and common wire and proceeds to the light.
  5. Once the current goes through the light fixture, it returns to the 2nd switch on the white wire. Then it is joined to another white wire. That is done in the 3 rope, which is between the switch boxes. After that, the current proceeds to the first switch box. There it is joined to the white power-in and goes back to the fuse box.
  6. After that process, the circuit is completed. There the bulb will light.

How does a 3-way switch work?

We have discussed all the details you need in order to understand more on three way switches. Now let’s understand how it works to bring light to our rooms. The 3-way switch has four screw terminals found on its body. The older switches don’t have the ground terminal. Each terminal has its role to play when it comes to the operation of the switch. In addition, there are wires that are used to connect to the terminals.

Wires; their colors and the role they play

  • The green or ground wire. This is the one that connects to the ground terminal.
  • The white wire is neutral. A wire nut is used to bundle it together.
  • The black wire is hot most of the time. The only exception is when the entire circuit is off.

The green screw terminal: Attached to the switch’s metal strap is always for the ground wire. The green terminal is where the connections happen. It is the framework of the entire 3 way switch.

Common terminal: This is the last terminal which is usually dark. Though the terminal is dark, the common terminal is darker. It comes in shades of brass, black, or copper. The main work of this terminal depends on its position in the circuit. Mainly it has two jobs; one of the jobs is accepting the incoming hot black wire that comes from the power source. The second job is to connect the hot black wire that goes to the light.

Traveler screws terminal: These are two, and you identify them because they are brass colored. In these traveler screws, some wires are connected. They are referred to as travel wires. For power to travel from one switch to the other, the wires create two different pathways. The positioning of these two screws depends entirely on the brands. Some have them on the same side, whereas others are on the opposite. In both cases, they work perfectly.

For the switch to work

The green wire is passed to the ground wire. All the light switches should have a ground terminal screw. This is for attaching the ground wire.

So from an electric view, the common terminal must be connected to traveler terminals. They usually are two, don’t forget.  If the switch flips on the other way, the connection is broken. That means the common terminal will be connected at that instance. That is done internally.

A point to note is that traveler terminals are interchangeable. Now that the common terminal must have a traveler wire attached, where the traveler wires are linked doesn’t matter. In other words, the travelers’ wires can be used at any place by the common travelers.

The Importance Of Installing The Ground Wire

I remember we pointed that you can do away with green screw terminals. A point of advice is that it helps in terms of safety. Note that it is connected to the metal strap. Though there are old switches that lack this terminal, you should always insist on having the one with it.

Final verdict

It is a bit complex to understand the 3-way switch works. But in our article, we have taken you through every step to help you know how it works. Every stage we have highlighted is essential because it will make you understand more. We have simplified our explanation but still maintained the vital bit. If you need to install the switch, you can always engage an electrician. But if you need to know how stuff work, read through this guide. Just to add on this, we have answered most of your questions.

About Linea Lorenzo

Linea was born to love drawing and just a few tech gadgets. While not working or sleeping, he often spends hours to look through the coolest, latest gadgets at different shopping sites, drooling about them. He also likes to keep things clean and tidy - now that the reason you see so many cleaning devices and electronics reviews at Ah yes, he made the site also just for that. Occationally, he invited friends to share their expertise around here too. Linea received Bachelor of Arts in Arts & Letters at Sacramento State University.

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