Categories
Self-organization

How three-way light switches work

How three-way light switches work

A three-way wall switch is a common type of light switch that makes it possible to control a ceiling light or other electrical fixture from two different locations in a room. In a hallway or large room, for example, installing three-way switches at both ends lets you turn the light fixture on or off from both locations. Three-way switches are always used in pairs and include special wiring connections.

What Is a Three-Way Switch?

The three-way switch is a variation of the standard single-pole switch, which controls a light only from one location. Three-way switches control a light fixture from two locations in a room.

Another type is the four-way switch, which is used in conjunction with two three-way switches to control lighting from more than two locations. This configuration may be used in open-plan homes or in large kitchens or great rooms, where a central bank of lighting fixtures might be controlled from more than two entry points.

Watch Now: 5 Main Types of Electrical Switches Explained

Three-Way Switch Screw Terminals

If you examine a three-way switch, you will notice several differences when compared to standard single-pole switches. First, the body of the switch will be thicker and bulkier than that of a single-pole switch. Also, the switch toggle lever on a three-way does not have the ON-OFF markings found on a single-pole switch. This is because the switch may turn the light on or off in either position, depending on the position of the other three-way switch in the pair.

The biggest difference between switch types is found in the screw terminals. While standard single-pole switches have two screw terminals on one side of the switch, plus a third green grounding screw terminal connected to the metal strap, three-way switches have three screw terminals plus a ground screw.

One of the screw terminals is a darker color than the other two terminals. The darker terminal is known as the common connection of the switch. Depending on where the switch will be in the circuit layout, the purpose of this common connection is to deliver electrical current from the power source (the circuit-breaker box) either to one of the switches or to deliver the current onward from the second switch to the light fixture.

The other two screw terminals on the switch body usually are brass-colored and are used to connect the circuit wires that run between the two three-way switches. These are known as the traveler terminals, and the wires running between the switches are known as traveler wires.

In a circuit situation, the traveler wires typically will have black and red insulation. When the switches are installed, these wires allow electrical current to pass between the switches—or they interrupt the circuit flow to turn the light fixture off. At any given moment when the light fixture is on, the power may be flowing through either the black or the red traveler wire. This will vary depending on the positions the switch toggle levers.

Three-Way Switch Wire Connections

Three-way switches have different methods of connection, depending on the brand of the switch. The switch may also have several ways to make the wire connections. All switches have screws on the side, but some also come with push-fitting holes or slots to slide the wire into. Still others come with a quick-mount, spring-loaded slot alongside the screw terminals that are designed to hold the wires in place.

Although these push fittings or slot-fittings may be the quickest way to connect a switch, this method is not recommended, as it is generally less secure. Professional electricians who want to avoid callbacks always use the screw terminal connections, which rarely come loose.

Tips for Replacing Three-Way Switches

Three-way switches are tricky to install, especially for DIYers who are replacing a bad switch. One of the most common problems is improper wiring due to connecting the circuit wires to the wrong screw terminals. It’s very easy to mix up three-way switch wiring when replacing a three-way switch, especially because in older wiring systems the standard color-coding of wires may look different than it does in newer installations.

The best way to get the wiring right is to take the time to mark the wires before you remove any from the old switch. The wire connected to the common screw terminal is the most important to mark. It must always connect to the darkest-colored terminal screw. By placing a colored piece of tape or label on the wire, it will be easy to find when you connect the new switch.

It’s also a good idea remove and reconnect one wire at a time when replacing switches. By doing this one wire at a time, you can ensure you are connecting the new switch correctly. This can sometimes be difficult, though, if the circuit wires in the wall box are too short—in this case, marking the wires is essential.

How three-way light switches work

­In your house or apartment, you probably have at least one light that is controlled by two separate switches. Whenever you flip either one of the switches, the light changes its state — if it is on it turns off, and if it is off it turns on.

If you have ever wondered ­how this arrangement works and how each switch knows what the other switch is doing, then read on. In this article, we will solve the mystery of three-way switches!

  • About
  • Podcasts
  • Privacy Policy
  • Ad Choices
  • Terms
  • Sitemap
  • Careers
  • Contact Us
  • Help
  • Reprints
  • Do Not Sell My Info

Newsletter

Get the best of HowStuffWorks by email!

Keep up to date on: Latest Buzz · Stuff Shows & Podcasts · Tours · Weird & Wacky

Copyright © 2020 HowStuffWorks, a division of InfoSpace Holdings, LLC, a System1 Company

We use cookies to personalise content and ads, to provide social media features and to analyse our traffic. We also share information about your use of our site with our social media, advertising and analytics partners who may combine it with other information that you’ve provided to them or that they’ve collected from your use of their services. You consent to our cookies if you continue to use our website.

Do not sell my data

  • Type of browser and its settings
  • Information about the device’s operating system
  • Cookie information
  • Information about other identifiers assigned to the device
  • The IP address from which the device accesses a client’s website or mobile application
  • Information about the user’s activity on that device, including web pages and mobile apps visited or used
  • Information about the geographic location of the device when it accesses a website or mobile application

Normal Lights

How three-way light switches work

Let’s start by looking at how a normal light is wired so that you can understand basic residential wiring for a light switch. The figure below shows the simplest possible configuration:

In this diagram, the black wire is “hot.” That is, it carries the 120-volt AC current. The white wire is neutral. (For more information on household AC current and grounding, see How Power Distribution Grids Work.) You can see in the figure that the current runs through the switch. The switch simply opens (off) or closes (on) the connection between the two terminals on the switch. When the switch is on, current flows along the black wire through the switch to the light, and then returns to ground through the white wire to complete the circuit.

The electrician who wires the house normally uses non-metallic sheathed cable, which most people know by the brand name Romex, to run power from the fuse box to the switches and outlets in the house. A piece of this cable is shown here:

How three-way light switches work

This cable consists of an outer plastic sheath (white in this picture) with three wires inside. The black and white wires are insulated, while a bare, third wire acts as the grounding wire for the circuit. Most normal household applications use 12- or 14-gauge cable.

  • About
  • Podcasts
  • Privacy Policy
  • Ad Choices
  • Terms
  • Sitemap
  • Careers
  • Contact Us
  • Help
  • Reprints
  • Do Not Sell My Info

Newsletter

Get the best of HowStuffWorks by email!

Keep up to date on: Latest Buzz · Stuff Shows & Podcasts · Tours · Weird & Wacky

Copyright © 2020 HowStuffWorks, a division of InfoSpace Holdings, LLC, a System1 Company

We use cookies to personalise content and ads, to provide social media features and to analyse our traffic. We also share information about your use of our site with our social media, advertising and analytics partners who may combine it with other information that you’ve provided to them or that they’ve collected from your use of their services. You consent to our cookies if you continue to use our website.

Do not sell my data

  • Type of browser and its settings
  • Information about the device’s operating system
  • Cookie information
  • Information about other identifiers assigned to the device
  • The IP address from which the device accesses a client’s website or mobile application
  • Information about the user’s activity on that device, including web pages and mobile apps visited or used
  • Information about the geographic location of the device when it accesses a website or mobile application

@craigelloyd
November 29, 2017, 3:00pm EDT

How three-way light switches work

If there are lights in your house that can be controlled from two different light switches (as opposed to just one), then the light is commonly referred to as a three-way light, and the switches are referred to as three-way light switches. Here’s how they work.

If you know anything about circuitry, then you at least probably know that an on/off switch is perhaps the simplest piece of circuitry there is. But once you add in a second switch to control the same object, things can get a bit complicated.

How a Light Switch Works

Before explaining how three-way light switches work, it’s important to know how a regular light switch works. These are called single-pole light switches, and they can turn on or off a light fixture from a single location. These are the most common types of light switches and are mostly found in bedrooms, bathrooms, and other simple room layouts where you would really only need one light switch.

Note: In the diagrams below, the neutral “return” wires and ground wires aren’t shown in order to make the diagrams as easy as possible to understand. If you’re worried about this, just know that the neutral “return” wire in the circuit doesn’t connect to any of the switches and simply continues on, whereas ground wires will connect to the green screw on every switch.

How three-way light switches work

In a traditional wiring setup with a single light fixture and a single switch, you have a hot wire coming in from the electrical panel that supplies the power to the light fixture. However, a light switch is installed in line with that hot wire. So when the light switch is off, it breaks the connection of the hot wire so that power can’t get to the light fixture. When the switch is turned on, the hot wire is reconnected, thus supplying power to the light fixture.

Adding in a Second Light Switch

Things get a bit complicated when you introduce a second light switch into the mix, but it’s still pretty simple once you know how it all works.

A three-way light switch is different than a traditional single-pole light switch, as it contains an extra screw to connect an extra wire. This is known as the “common” screw and it’s usually black (instead of brass or silver). Another dead giveaway of a three-way switch is the absence of “On” and “Off” markings.

How three-way light switches work

This is why whenever you need to replace a light switch in your house, it’s important that you get the right kind of light switch, since you can’t use a single-pole switch in a three-way circuit.

The diagram below provides a simple layout of a three-way light setup, and you can see the red wire is the extra wire that’s needed to make it all happen (conveniently enough, red wire is normally used in real life in three-way circuits as well).

How three-way light switches work

How it works is that the hot wire coming in from the electrical panel is connected to the common screw of the first light switch in the circuit.

On the other side of this switch are two brass screws. The “traveler wires” (a.k.a. the wires that connect the two light switches to each other) attach to these two screws, and it doesn’t matter which of the two screws they each connect to.

On the other switch, the hot wire that continues on to the light fixture attaches to the common screw. And as with the previous switch, the two traveler wires will connect to the two brass screws (again, in no particular order).

This wiring setup uses the two traveler wires to allow for either light switch to control the light fixture. Not only that, but this also allows you to turn on the light from one switch and turn it off from the other switch. For example, the diagram below shows the inside of each switch and their “on/off” positions.

How three-way light switches work

Currently, each switch is in a different state, but thanks to the top traveler wire, the circuit is still complete and the light is on. Flipping either of the switches will break the circuit and turn the light off. However, if you were to flip the other switch, then the circuit would use the red traveler wire this time and the light would turn back on.

It sounds complicated at first, but as you’ve now discovered, it’s actually pretty simple.

Beyond Three-Way Light Switches

Three-way lights are fairly common in a lot of larger houses, but you might also find four-way, or even five-way lights, in some houses.

Four-way circuits are just a tad different than three-way circuits, mostly since the light switch that you add in has to be a four-way switch rather than just another three-way switch. A four-way switch has an extra common screw to bring the total number of screws up to four: two common screws and two brass screws (not counting the ground screw).

How three-way light switches work

This allows for the two traveler wires to travel through the four-way switch and onto the next switch in the circuit, which means four wires will connect to this switch rather than just three.

From there, you can add on as many four-way switches as you want, just as long as there are three-way switches on either end. You shouldn’t have to worry about anything more than a four-way circuit, though, as five-way circuits and higher are fairly uncommon in most residential households.

If there are lights in your house that can be controlled from two different light switches (as opposed to just one), then the light is commonly referred to as a three-way light, and the switches are referred to as three-way light switches. Here’s how they work.

If you know anything about circuitry, then you at least probably know that an on/off switch is perhaps the simplest piece of circuitry there is. But once you add in a second switch to control the same object, things can get a bit complicated.

How a Light Switch Works
Before explaining how three-way light switches work, it’s important to know how a regular light switch works. These are called single-pole light switches, and they can turn on or off a light fixture from a single location. These are the most common types of light switches and are mostly found in bedrooms, bathrooms, and other simple room layouts where you would really only need one light switch.

Note: In the diagrams below, the neutral “return” wires and ground wires aren’t shown in order to make the diagrams as easy as possible to understand. If you’re worried about this, just know that the neutral “return” wire in the circuit doesn’t connect to any of the switches and simply continues on, whereas ground wires will connect to the green screw on every switch.
How three-way light switches work
In a traditional wiring setup with a single light fixture and a single switch, you have a hot wire coming in from the electrical panel that supplies the power to the light fixture. However, a light switch is installed in line with that hot wire. So when the light switch is off, it breaks the connection of the hot wire so that power can’t get to the light fixture. When the switch is turned on, the hot wire is reconnected, thus supplying power to the light fixture.

Adding in a Second Light Switch
Things get a bit complicated when you introduce a second light switch into the mix, but it’s still pretty simple once you know how it all works.

A three-way light switch is different than a traditional single-pole light switch, as it contains an extra screw to connect an extra wire. This is known as the “common” screw and it’s usually black (instead of brass or silver). Another dead giveaway of a three-way switch is the absence of “On” and “Off” markings.

This is why whenever you need to replace a light switch in your house, it’s important that you get the right kind of light switch, since you can’t use a single-pole switch in a three-way circuit.

The diagram below provides a simple layout of a three-way light setup, and you can see the red wire is the extra wire that’s needed to make it all happen (conveniently enough, red wire is normally used in real life in three-way circuits as well).
How three-way light switches work
How it works is that the hot wire coming in from the electrical panel is connected to the common screw of the first light switch in the circuit.

On the other side of this switch are two brass screws. The “traveler wires” (a.k.a. the wires that connect the two light switches to each other) attach to these two screws, and it doesn’t matter which of the two screws they each connect to.

On the other switch, the hot wire that continues on to the light fixture attaches to the common screw. And as with the previous switch, the two traveler wires will connect to the two brass screws (again, in no particular order).

This wiring setup uses the two traveler wires to allow for either light switch to control the light fixture. Not only that, but this also allows you to turn on the light from one switch and turn it off from the other switch. For example, the diagram below shows the inside of each switch and their “on/off” positions.
How three-way light switches work
Currently, each switch is in a different state, but thanks to the top traveler wire, the circuit is still complete and the light is on. Flipping either of the switches will break the circuit and turn the light off. However, if you were to flip the other switch, then the circuit would use the red traveler wire this time and the light would turn back on.

It sounds complicated at first, but as you’ve now discovered, it’s actually pretty simple.

Beyond Three-Way Light Switches
Three-way lights are fairly common in a lot of larger houses, but you might also find four-way, or even five-way lights, in some houses.

Four-way circuits are just a tad different than three-way circuits, mostly since the light switch that you add in has to be a four-way switch rather than just another three-way switch. A four-way switch has an extra common screw to bring the total number of screws up to four: two common screws and two brass screws (not counting the ground screw).
How three-way light switches work
This allows for the two traveler wires to travel through the four-way switch and onto the next switch in the circuit, which means four wires will connect to this switch rather than just three.

From there, you can add on as many four-way switches as you want, just as long as there are three-way switches on either end. You shouldn’t have to worry about anything more than a four-way circuit, though, as five-way circuits and higher are fairly uncommon in most residential households.

Switches that are sensitive to human touch — as opposed to switches that must be flipped or pushed to make and break a mechanical connection — have been around for many years. They certainly have advantages, and the most important is the fact that dirt and moisture cannot get into the switch to gum it up or damage it. Over the years, many different properties of the human body have been used to flip touch-sensitive switches:

  • Temperature – The human body is generally warmer than the surrounding air. Many elevators therefore use buttons that are sensitive to the warmth of the human finger. These buttons, of course, don’t work if you have cold hands. The motion-sensitive lamps you see on people’s patios also sense the heat of the human body.
  • Resistance – The human body, being made mostly of water, conducts electricity fairly well. By placing two contacts very close together, your finger can close the circuit when you touch it.
  • Radio reception – You may have noticed that, when you touch an antenna, the reception gets better on a TV or radio. That’s because the human body makes a pretty good antenna. There are even small LCD TVs that have a conductive neck strap so that the user acts as the antenna! Some touch-sensitive switch designs simply look for a change in radio-wave reception that occurs when the switch is touched.

Touch-sensitive lamps almost always use a fourth property of the human body — its capacitance. The word “capacitance” has as its root the word “capacity” — capacitance is the capacity an object has to hold electrons. The lamp, when standing by itself on a table, has a certain capacitance. This means that if a circuit tried to charge the lamp with electrons, it would take a certain number to “fill it.” When you touch the lamp, your body adds to its capacity. It takes more electrons to fill you and the lamp, and the circuit detects that difference. It is even possible to buy little plug-in boxes that can turn any lamp into a touch-sensitive lamp. They work on the same principle.

Many touch-sensitive lamps have three brightness settings even though they do not use three-way bulbs. The circuit is changing the brightness of the lamp by changing the “duty cycle” of the power reaching the bulb. A bulb with a normal light switch gets “full power.” Imagine, however, that you were you were to rapidly turn the power to the bulb on and off (say 100 times per second) — then the bulb would only burn half as brightly because its duty cycle is 50 percent (half on, half off). “Rapidly switching the bulb on and off” is the basic idea used to change the brightness of the lamp — the circuit uses zero percent (off), 33 percent, 66 percent and 100 percent duty cycles to control the lamp’s brightness.

Related HowStuffWorks Articles

  • How Radio Works
  • How Television Works
  • How Light Works
  • How Force, Power, Torque and Energy Works
  • How LCDs Work
  • How Three-way Switches Work
  • How do touchscreen monitors know where you’re touching?

More Great Links

  • About
  • Podcasts
  • Privacy Policy
  • Ad Choices
  • Terms
  • Sitemap
  • Careers
  • Contact Us
  • Help
  • Reprints
  • Do Not Sell My Info

Newsletter

Get the best of HowStuffWorks by email!

Keep up to date on: Latest Buzz · Stuff Shows & Podcasts · Tours · Weird & Wacky

Copyright © 2020 HowStuffWorks, a division of InfoSpace Holdings, LLC, a System1 Company

We use cookies to personalise content and ads, to provide social media features and to analyse our traffic. We also share information about your use of our site with our social media, advertising and analytics partners who may combine it with other information that you’ve provided to them or that they’ve collected from your use of their services. You consent to our cookies if you continue to use our website.

Do not sell my data

  • Type of browser and its settings
  • Information about the device’s operating system
  • Cookie information
  • Information about other identifiers assigned to the device
  • The IP address from which the device accesses a client’s website or mobile application
  • Information about the user’s activity on that device, including web pages and mobile apps visited or used
  • Information about the geographic location of the device when it accesses a website or mobile application

How three-way light switches work

Introduction

Nowadays people are widely using the three way switches. However, the usage of two switches isn’t decreasing too.

Just from the name, we can assume that these switches are different. And that’s true Both these switches have different working principles.

We’re assuming that you are up to buying new switches. And we’re guessing that you’re in a dilemma about choosing between these two options.

To help you out we have crafted out this piece. Here we have discussed the difference between 2 way and 3 way light switch.

We have divided the discussion in two parts. In first part, we have a feature specific difference table. On the second, we have a working principle based discussion.

So, let’s get going without wasting any more time-

2 Way vs 3 Way Switch

Before jumping straight into the feature specific table, let’s go through some useful information. So, what is a 2 way switch?

The 2 way switch or single pole double throw switch is a three terminal switch. Here 1 terminal is the input and the other two are used as outputs. It’s okay if this is too complex for you. We’ll break it down pretty soon. Now, let’s look at the 3 way switch.

So, why is it called a 3 way switch?

Because it uses two switches and one appliance. In 3 way switches you use two control a single appliance from two different locations.

Now let’s look at the feature specific differences-

These have on/off switches

Do not have an on/off switch

These switches don’t have hot wires.

These switches have hot wires

These switches have 3 terminals

These switches actually have 4 terminals

These switches use only 2 types of wires.

These switches use 3 types of wires.

Installing 2 way switches are easy.

Installing 3 way switches are more complex.

Working Principles of 2 way and 3 Way Switches

Here we will try to explain how these switches work in the simplest possible way. But we always recommend you watching real live video tutorials about these.

So, let’s go through the switches one by one-

How 2 way Switch Works?

Let’s assume that 2 switches S1 and S2 are controlling a bulb. Now we have two types of wires coming to the switches. The neutral and the hot wire.

Each of the switches have 3 terminals. One is common and the other two are output. In 2 way switching, the live wire connects with the common terminal of S1. On the other hand, another hot wire connects the S2 common terminal and the bulb.

The remaining output terminals are connected with each other through two sets of wires.

The neutral wire goes directly to the bulb.

Now let’s name the output terminals as S1L1, S1L2, S2L1, and S2L2. It’s better if you draw a diagram at this point.

The terminals are named like this; Switch name – Terminal Number. So, S2L1 means the 1st terminal of Switch 2.

Now, if the switch terminal are disconnected in any combination, then the bulb will remain off. If the circuit gets completed, then we’ll see a lit bulb.

How does three way switch work?

The three way switch comes with three terminal screws and one ground wire screw. In total it has 4 terminal screws.

There’s a dark colored terminal named ‘COM’ in 3 way switches. The remaining two terminals are called as interchangeable and travelers.

You’ll typically find the traveler wires with black and red insulation. Once the switches are installed, these wires come do the main action. These wires pass or interrupt electrical current between the switches.

When the connected appliance or light fixture is on, the current goes through any of those black or red travelers.

Final Thoughts

We’re at the end our journey. We believe that now you can give out lecture on these switch types. However, don’t go on working on these switches if you’re not sure about some details.

Working with electricity is extremely dangerous.

However, if you’re thinking about installing light switches, then we would recommend 3 way switches. Because these are super safe.

Good luck and don’t forget to ask us about anything that seemed confusing to you.

How three-way light switches work

Test a 3- Way Switch

  1. Turn off power to the switches at the circuit breaker and using a tester, make sure power is off. Remove the two 3- way switches so you can access the switch terminals. The wire connections do not have to be removed.
  2. Using a continuity tester, check continuity between the common (black) terminal and each of the traveler terminals (brass colored) of each 3- way switch.
  3. There should be continuity between the common terminal and only one of the traveler terminals. After toggling the switch, there should be continuity between the common terminal and only the other traveler terminal.

When a 3- way switch fails, there will usually be no continuity between the common terminal and one (sometimes both) traveler terminals of one of the 3- way switches.

Place leads of continuity tester on the common (black) terminal and one of the traveler (brass or silver) terminals

Place leads of continuity tester on the common terminal and the other traveler terminal

Toggling 3- Way Switches

Locate a Bad 3- Way Switch

Usually when a 3- way switch fails, lights can be toggled on and off at one switch, but not the other. If one of the two 3- way switches toggles the light(s) on and off, the other 3- way switch has probably failed. Follow these steps to find which switch is bad.

  1. Toggle each switch until the light come on. Toggle one switch to see if it turns the light on and off. If it does, it is a good switch. Leave the light on.
  2. Toggle the other switch to see if it turns the light on and off. If it does, it is a good switch and the other is bad.

One of these switches will not turn the light on and off (while the light is on) and that is the bad switch.

Once you identify the bad switch, follow the steps below to verify it is bad and needs to be replaced.

Note: This article only applies to conventional 3- way switch wiring, and not alternate 3- way wiring.

Switches are spring loaded to minimize arching and prolong their life. However, a very small amount of arcing is present when a switch is toggled. A bad switch may not fail completely, burned contacts may cause intermittent failure. Keep this in mind when troubleshooting switches. Intermittent failure could make troubleshooting difficult, especially with 3 and 4- way switches. If one 3- way switch needs to be replaced, the other one should be replaced too.

How three-way light switches work

Black common wire is usually wrapped around the two traveler wires on a 3- way switch.

How three-way light switches work

Together, three-way bulbs and sockets provide a convenient method for choosing one of three levels of light output—lumens—from a single light bulb. For that reason, they are usually found in bedside lamps or floor lamps near a favorite chair. They’re also useful in a desk or table lamp.

Variable Light Output

Three-way bulbs are most often used where people tend to spend a fair amount of time doing a variety of activities, such as in the living room or den. For instance, reading print material is often better with a medium level of light. When watching TV or working with a backlit screen, you may prefer a lower level. If you’re doing a task which requires viewing it clearly, such as sewing, that’s when you’ll want more light.

With a three-way bulb in a three-way socket, those options are easy. Most often, this set up uses a bulb with a standard screw base (E26) and either 30/70/100 or 50/100/150 watts of power to produce the three levels of light.

Some floor lamps with a bowl-shaped shade take a larger PS25 bulb with a Mogul screw base (E39). These will generally use 100/200/300 watts of power to throw a lot of light up onto the wall and ceiling.

How Do They Work?

Screw base three-way light bulbs and sockets work by supplying power first to the low-wattage element or filament—the 30W or 50W or 100W element in the three examples above. It will then send power to the middle-wattage element or filament (the 70W or 100W or 200W element), and finally to both at once. That’s why the highest wattage for an incandescent or CFL three-way light bulb is the sum of the two lower wattages.

LED three-way light bulbs receive and apply power in the same way since that’s the way the sockets work. However, due to the different technology, the wattages don’t always add up, though they are close.

The variable output is achieved with two sets of contacts in the socket and on the base of the bulb.

Starting with the bulb, the threaded outside of the base—the part that screws in—is connected to the “neutral,” or grounded conductor in the power supply. The contacts for the “hot,” or ungrounded, conductor are at the end of the base. To see those, turn a light bulb upside down.

A standard screw base light bulb will have one metal contact in the center, with insulating material—usually molded glass—between that and the threaded metal shell. That’s the contact for the hot power.

A three-way screw base light bulb has the same center contact as a regular light bulb. It’s in the center of the base and it’s usually pretty small. That’s where the power connects to the middle-wattage element in the bulb. There’s a ring of insulating glass around that, then a metal ring, and then a second insulating ring before you get to the threaded shell. That isolated metal ring is the second contact. That’s where the power is connected to the low-wattage element in the light bulb.

In every screw base socket, there’s a center contact to match the one on every screw base bulb. In a three-way socket there is a second contact to supply power to the ring-shaped contact on the base of the three-way bulb. It’s a little tab, and it’s sitting to one side, midway between the center contact and the shell of the socket.

When You Turn the Switch

Electrical switches work by connecting and disconnecting the circuit from the panel to the load and back again.

  1. When you turn the switch control on a three-way socket one click from “off,” the switch connects power to the socket’s tab-shaped contact. This sends power to the bulb’s ring-shaped contact and its lower-wattage element.
  2. When you turn it one more click, it disconnects the tab and connects the power to the center contact. That takes it to the higher-wattage element in the bulb.
  3. Turning the switch one more time connects power to both the tab and the center point contacts. Both of the elements in the bulb have power at the same time, using the maximum wattage.
  4. One last click of the switch disconnects all of the power, and the light bulb goes off.

Off-On-On-Off Pattern

If you think this through, you’ll see that the switch in a three-way socket is sending the power to the lower-wattage element in an on-off-on-off pattern. It’s also sending power to the middle-wattage element in an off-on-on-off pattern.

If you have a bulb in a three-way socket that’s going off-on-on-off, one of three things is happening:

  • The bulb may be a standard bulb rather than a three-way bulb.
  • The lower-wattage element in the three-way bulb may have burned out.
  • The contact for the lower-wattage element may be defective.

It’s usually pretty easy to troubleshoot and fix the problem and fix or repair it. Take it one step at a time and you’ll have your favorite lamp functioning on all three “speeds” again.

How to Wire a Three Way Switch – Diagram, Tutorial & Lighting

The Purpose of a Three Way Electrical Switch

Knowing how to wire a three-way lighting switch comes down to understanding the operation of this contraption. A three-way switch is fundamentally different in its operation from a regular two-way switch. you must completely forget about the notion of a switch being a simple open/closed circuit and look at the diagram of the circuitry of this modern alternative.

The goal is to place two switches at separate locations which control the exact same device. Usually, it is a light source, but it can be anything which requires a phase and a neutral to operate.

How Does a Three Way Switch Work

How three-way light switches workA typical three-way switch will have, you guessed it… Three terminals. See the description of each one of them below.

The principle is that the switch will have one main input terminal and two output terminals. In each position (ON/OFF), the switch will connect the input to only one of the outputs. In other words, the current will always flow from one input pin to either output pin.

The main input terminal is critical. It will usually be marked by the fact that the terminal screw is colored black. The other two will be left as is (brass).

Terminal 1 Input Terminal (Black Screw) – This terminal is used as an input. It is where you connect the wire which needs to be switched.

Terminal 2 Output Terminal – This terminal is used as an output. In the initial state, the current will flow from Terminal 1, into Terminal 2.

Terminal 3 Output Terminal – This terminal is used as an output. When the switch is toggled, the current will flow from Terminal 1 into Terminal 3.

How to Wire a Three Way Switch

Now that you understand how a three-way switch works, it’s time to get into the wiring of two switches which control a single light source.

Although we have provided you with a diagram above, here’s another look at what the circuit is like. Below the diagram, you will find easy to follow steps which will guide you through the process.

How three-way light switches work

The diagram above may not seem obvious at first. Read through the following steps in order to understand what needs to be done.

Step 1 – The breaker phase (black wire), neutral (white wire), as well as the ground (green wire), must be landed in the first switch enclosure.

Step 2 – Connect the black wire to the Input 1 of your switch. Secure the white wire to the second wire with the same color using a wire nut.

Step 3 – Connect the secondary cable (going from Enclosure 1 to the light) to Output 1 and Output 2 on the switch.

Step 4 – Inside the light enclosure, connect the neutral (from the secondary wire) to the light. Connect the black conductor to a white conductor of a tertiary cable. Connect the red conductor to the red conductor on the tertiary cable. Connect the black conductor of the tertiary cable to the light terminal.

Step 5 – Inside the second switch panel, connect the black conductor to Input 1. Connect the other two wires (white and red) to the brass terminals.

At this point, you should have a light which may be controlled independently by one of the two switches. If you are having trouble, I recommend going back to the diagram to review your connections. Make sure that you got the colors right as they do switch inside the lightbox.

Keep in mind that as you work with this switching system, you can choose to go Switch – Switch – Light instead of Switch – Light – Switch. If you understand the fundamentals of the circuit itself, the possibilities are endless.

Recommended Reliable Three Way Switches

Once you have mastered the technique above, you will begin installing three-way switches all over the house. Here’s a short review guide on some of the switches I have personally used and relied on just like many other electricians in the field.