How To Wire A 3 Way Switch - Wiring Diagram

Wiring a 3 way switch

How to wire a three way light switch is not a particularly difficult task - there are only 3 connections to be made, after all. Making them at the proper place is a little more difficult, but still within the capabilities of most homeowners - that's where understanding a wiring diagram can be of help.

To replace a switch is not difficult at all; simply put the wires back on the new light switch in the same relative position. The problems arise when a new switch is being added, or the handyman forgets which wire went where. Then it is necessary to understand a little more just how a three way switch works, and perhaps how to read and understand a wiring diagram.

There are many possibilities for methods of getting the proper wire to the proper place but in every case the actual wiring has the same effect and uses the same concept - if that effect and concept is known the task becomes much simpler. This article is designed to explain these things for a better understanding of how to wire a 3 way switch, and wiring diagrams are shown for common wiring methods for these switches.

4 way switches are often used in conjunction with three way switches; whenever more than 2 switches are used to control a single light fixture the additional switches are of the 4 way variety. Additional information is available in the article written on how to wire a 4 way switch, with additional wiring diagrams for these switches.

3 way switches

An old switch.  This switch has no ground screw and is no legal longer to use.  Make sure your switch has a ground terminal.
An old switch. This switch has no ground screw and is no legal longer to use. Make sure your switch has a ground terminal. | Source
The common terminal is on the top in this view, with a traveler on the lower end.  The ground screw is showing up as silver colored at the very bottom.
The common terminal is on the top in this view, with a traveler on the lower end. The ground screw is showing up as silver colored at the very bottom. | Source
All three terminals are visible here.  The ground screw is on the top side of the switch.
All three terminals are visible here. The ground screw is on the top side of the switch. | Source

How a 3 way switch works

The photos to the right show the back of a 3 way switch. There are 3 screw terminals on the sides of the switch, along with one on the end, and every switch will have the same three terminals. The small screw terminal on the end is the ground terminal and is usually painted green, although the picture does not show that color well. It can often be recognized as the screw that is part of the metal framework of the switch and is not insulated from other metal parts. The green, or bare of insulation, ground wire always goes to this terminal. Older switches often did not have this ground screw, but are no longer legal to use and all current light switches must have a ground screw to attach the ground wire to.

One of the three other terminals is a different color, usually darker, and is called the common terminal. Mechanically and electrically this common terminal is connected internally to one of the other two brass screws, called the traveler terminals. When the switch is flipped the other way that connection is broken, and the common terminal is then connected to the other traveler terminal. This common terminal is always connected internally to one (but only one) of the traveler terminals; which one is dependent on whether the switch is up or down.

It should perhaps be noted that the traveler terminals are essentially interchangeable. Given that each one is to have a traveler wire attached to it, and there are two traveler wires and terminals, it doesn't matter which traveler wire goes to which traveler terminal.

Terminology of the 3 way light switch

The terms "traveler" and "common" have already been explained, but there are other terms that will be used in this article that also need some explanation.

  • Cable. The term "cable" refers to an assembly of two or more wires, bundled together, usually in a sheath of insulating material. Each wire is insulated separately, with the possible exception of the ground wire. This wire may be insulated with a green color or left bare, without insulation.
  • Power in. The power in cable is that cable that eventually ends in the circuit breaker panel, or fuse box. It is the cable that provides the power to the lighting system.
  • Neutral. This is the white wire contained in the power in cable. It does not terminate at any switch, although it may be present in a switch box and spliced straight through the box.
  • Ground. The grounded wire in each switch or light fixture box. It is either colored green or left bare of insulation
  • Hot wire. This is the second, black wire, contained in the "power in" cable. It is "hot" at all times unless the entire circuit is turned off at the circuit breaker panel
  • Circuit breaker panel. Commonly called a "fuse box" it may contain either circuit breakers or fuses. This panel is where all the power in the building is derived, and where that power may be shut off.
  • Two rope. Two rope is the designation given to a cable that has two individual wires, plus a ground wire. These wires will be colored white and black, with a green or bare ground.
  • Three rope. Three rope is a cable with three wires, plus a ground. Normally the colors are white, black and red with an additional green or bare ground.

Understanding a wiring diagram

Each diagram will show the two 3 way switches (but not the wall box they are contained in), the various cables and wires used in the configuration being discussed, the light box and light fixture.

To understand the wiring diagram, it must be realized that the electrical current enters the system on the black wire in the power in cable, passes through the switches, through the light fixture, and returns to the white wire in the power in cable. If the circuit is broken anywhere (a switch turned the wrong way, a broken wire, or a bad light bulb) the current will not flow and the light bulb will not light. For discussion purposes, each 3 way switch will be considered to have the common terminal connected to the right hand traveler terminal when in the "up" position and connected to the left hand terminal when in the "down" position. This is not necessarily true, and the convention is only for discussion purposes.

Read the descriptions carefully, and compare them to the diagrams to understand the diagrams. Each diagram will have a description of how the current travels in order to light the lamp.

Voltage Testers

A non-contact voltage tester is an invaluable tool here for working on electrical circuits. Both Fluke and Klein make professional quality testers, and cheaper ones are commonly available as well.

Installing the light switch

Once the correct location of each wire is determined, using the wiring diagrams below, the light switch is connected to proper wires and installed in the light switch box. Make sure the power is off before making any connections!

Many residential light switches have a small hole in the back of the switch that wires can be pushed into, and all switches have the screws on the side as shown above. The picture of the older switch above has both the push in holes and screws; the other is an expensive switch that has holes to insert wire but the screws must be tightened as well. Many switches have only the screws, with no holes. There is a "strip gage" on the back of the switch; it shows how much insulation is to be stripped off if the push in method of connection is to be used. If the screws are to be used, a little more insulation needs removed.

If the screws are to be used for connection, bend the end of the stripped wire into a half circle, using needle nose pliers, and wrap the wire around the screw in the clockwise direction. Tighten each screw firmly. Fold the wires neatly back into the wall box and push the switch into the box. Normally the ground screw goes down, toward the floor, but it can be inserted in the up position with 3 way and 4 way switches.

3 way wiring diagram #1

3 way switch wiring diagram with the power in cable entering the light box.
3 way switch wiring diagram with the power in cable entering the light box.

Wiring diagram #1, power in the light box

In this example the power in cable enters the light box. This method of running the wire is commonly found when several light fixtures are on one common breaker, and switches for the one in question are both on the same wall. Cables need to be run into the light box, between the two switches, and from the light box to just one of the switches.

Lets follow the current as it lights the lamp in the light fixture. The current enters the light box on a black wire, as it always does. That wire is spliced to a white wire in a two rope cable that goes to the first switch box (not the switch) where it is spliced to the white wire in a three rope cable and continues on to the second switch, at the common terminal. If the switch is up (remember our assumption above?) it will exit the switch on the right hand traveler terminal and continue on the red wire back to the traveler terminal on the first switch. If that switch is also up it will exit that switch from the common terminal on the black wire in the two rope cable from the light switch. Continuing down that black wire it enters the light box, where it goes to the light fixture. The current will pass through the light, exiting the light on the white, neutral, wire and return to the power in cable.

A note about wire colors. The National Electric Code requires that every neutral wire be colored white, and that ground wires be colored green. Only neutral wires may be white in color, but the code makes an exception for white wires in a cable that are not being used for a neutral. These wires (in our example the white wire from the light box to the switch box and from that box to the second switch box) should be colored black (or some other color), using a magic marker or some other method. Many electricians will do this, but many will not, and it can make trouble shooting in the future difficult and can be a safety hazard to anyone else working on the system. I encourage you to take the few seconds necessary to color these non-neutral wires. In this example the only neutral wires are the white wire in the "power in" cable (which is always a white wire) and one of the two wires attached to the light (also always white). All other white wires should be colored.

In addition, the colors shown in these wiring diagrams are common color usages only. Not all electricians use the same color code (except for neutrals and grounds), so the wires could be different colors.

3 way wiring diagram #2

3 way switch wiring - power again in the light box, with 3 rope cables to each switch box.
3 way switch wiring - power again in the light box, with 3 rope cables to each switch box.

Wiring diagram #2, power in light box

In this 3 way switch wiring diagram the power in line again enters the light box, but 3 rope cables are then installed between the light box and each switch box.  This method might be used when power is available in the ceiling but switch boxes are on opposite walls - it is often easier to run the cable up into the ceiling to the light box instead of between switches.

If the current is again followed, it comes into the light box on the black wire, and to the common terminal on one switch using a (colored) white wire.  Exiting the switch from a traveler terminal it then returns to the light box, but is merely spliced to another wire that goes to a traveler terminal on the second switch. It goes through the switch, again exiting from the common terminal, and once more enters the light box where it goes to the light itself.  The neutral once more goes from the power in cable directly to the light fixture.

3 way wiring diagram #3

3 way wiring diagram with power entering switch #1
3 way wiring diagram with power entering switch #1

Wiring diagram #3

This time the electrician has brought power into the first switch, through the second switch and on to the light fixture.  This is a reasonable method for cases with multiple switches in the same box, as other switches then have power available and can operate other lights without having to have a separate power in line run to them.

The major difference here is that the neutral from the power in line has to be taken to the light fixture via the 3 rope.  The white wire must be used here as code requires that all neutral wires be white.

Following the current, it enters the first switch box on the black wire and is connected to the common terminal.  If the switch is in the "down" position it exits the switch on the red wire, entering the second switch at a traveler terminal.  If that switch is also down it exits that switch on the black, common, wire and continues to the light.  After passing through the light fixture the current returns to the second switch box on the white wire, is spliced to another white wire in the 3 rope used between switch boxes and continues to the first switch box where it is spliced to the white power in wire and back to the fuse box.  The circuit is complete and the lamp will light. 

3 way wiring diagram #4

3 way wiring - power in once more enters switch #1, along with a cable to the light box.
3 way wiring - power in once more enters switch #1, along with a cable to the light box.

Wiring diagram #4

This example shows the power in cable once more entering the first switch box, along with the cable to the light fixture.  This can result in a lot of wires in this box, but can be helpful when the light is near the first switch box.  A larger box may be necessary to contain all the wires.

Following the current for a last time, it enters the switch box on the black wire at the common terminal.  If the switch is up it will exit the box on the red traveler wire and continue to the traveler terminal at the second switch.  If that switch is also up it will exit the switch at the common terminal on the white (colored) wire and return to the first switch box where it is spliced to the black wire in the 2 rope going to the light.  Passing through the lamp, it returns on the white (neutral) wire to the first switch box, is spliced to the white (neutral) wire returning to the fuse box.  Once more the circuit is complete and the lamp lights up.

Commonality in all wiring diagrams

  • Common to all of these wiring diagrams is that the neutral, white, wire from the lamp connects directly to the white, neutral, wire from the power in cable without ever terminating on a switch. It may or may not be spliced to another white wire in a box, but never terminates on a switch - only on the light fixture.
  • The power in, black, wire always goes to the common on a switch, often "changing colors" through the necessity of splicing to different cables. No matter what color, one switch will have a common terminal connected directly to the power in black wire.
  • The other common terminal on the other switch always goes directly (although perhaps again spliced) to the light fixture. It does not terminate on the other switch.
  • There are two traveler wires; they always go directly from one switch to the other. Neither traveler wire ever terminates at the light fixture, the power in cable, or on anything but a traveler terminal, although it may splice to a different cable somewhere.
  • Neutral wires are always white, and white wires not connected to the white power in wire should be colored some other color.
  • Ground wires are always green or bare of insulation. Each switch, as well as the light fixture, must have a ground wire terminated to it. The only exception is older homes that do not have ground wires in the boxes; if there is a ground wire in the box it must be terminated on the switch and light.

A final note; recent code changes require that each switch box have a neutral wire in it. This means not only a white wire, but a white wire that is connected to the white wire on the power in cable. It is intended to provide future capability for the use of a dimmer or other device that may need a neutral wire and to put a stop to homeowners disconnecting or using the ground wire for purposes other than providing the necessary ground to switches or lights. New work such as adding a new three way switch or a room addition with 3 way switching will need to comply with this code. The only wiring diagram shown here that is legal to use is #3, although #1 could be modified by adding a 2 wire cable from the lower box to the light. Any neutrals in the switch box that are unused are either spliced together or, in the case of a single neutral, simply capped off with a wire nut and tucked back into the box. Simply replacing a switch does not mean that the room needs to be re-wired as the existing wiring is "grandfathered" and is acceptable. Old work does not need to be re-done to comply with the code and is why the unacceptable (by current code) wiring diagrams are discussed.

Conclusion of wiring a 3 way switch

Switches in general are not difficult to replace or install, and most homeowners are quite capable of replacing a light switch. Those people adding a new light fixture, with associated 3 way switches, have hopefully found this article useful and informative.

Any of the different methods of wiring a 3 way switch shown here can be used interchangeably in old work; they merely indicate different ways to run the necessary cables. Actually wiring the switches is always the same, the different methods simply can result in easier or cheaper ways to install the cabling necessary, but keep in mind the mention above that new work must always have a neutral wire in the switch box, whether it is actually used or not.

Regardless of whether you are replacing a switch or installing new switches in a major room remodel, probably the most useful tool you might own is a non contact AC voltage detector. Make sure that whenever doing any kind of electrical work that a good voltage detector is available - it can save a lot of grief.

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Comments 48 comments

dallas93444 profile image

dallas93444 6 years ago from Bakersfield, CA

As a licensed California Contractor, I thought I knew basic wiring. I purchased what I thought was a three-way switch. Imagine my frustration after checking my wiring three times, I checked the three-way switch to determine it was a normal single pole, on-off two-way switch... Great information for those who understand the concept of wiring...

wilderness profile image

wilderness 6 years ago from Boise, Idaho Author

Thank you for the compliment. Wiring a 3 way switch is just enough different that many people have trouble with it. My hope is that the diagrams and explanations will make it understandable for those that have even a modicum of experience there.

At least you found your problem; many end up hiring an electrician to to a 5 minute job!

dgicre profile image

dgicre 6 years ago from USA

This is great! Very common problem and hooking 3/way switches up the wrong way leads to some interesting and often frustrating experiences.

wilderness profile image

wilderness 6 years ago from Boise, Idaho Author

You are absolutely right in that it can be very frustrating. I once tried to trouble shoot a friend's work and he had installed a 4 way instead of a 3 way (which is possible and will work) but had it wired wrong. It looked right if you didn't notice the 4th screw, but wouldn't work properly. Almost 2 hours of tearing all the switches and 4 little can lights apart before I noticed his error! Extremely frustrating!

stars439 profile image

stars439 6 years ago from Louisiana, The Magnolia and Pelican State.

Great information. GBY

wilderness profile image

wilderness 6 years ago from Boise, Idaho Author

Thank you. I can only hope that someone will find it useful in wiring a 3 way switch.

wilderness profile image

wilderness 5 years ago from Boise, Idaho Author

That's good to hear. Thanks for the comment - I appreciate it when someone lets me know I helped them out.

tamron profile image

tamron 5 years ago

I pinged ya! well done and well written electrical article!

wilderness profile image

wilderness 5 years ago from Boise, Idaho Author

Thank you, both for the ping and the compliment.

whitton profile image

whitton 5 years ago

Thank you for this very informative Hub.

wilderness profile image

wilderness 5 years ago from Boise, Idaho Author

Thanks for the comment - I hope you will find a use for the information.

Manna in the wild profile image

Manna in the wild 5 years ago from Australia

This is useful. Thanks.

imamsaheb 5 years ago

when i look the connectipons to learn simplify,so thanks u

wilderness profile image

wilderness 5 years ago from Boise, Idaho Author

Thanks to the both of you for the comment; it helps to know that you find the information useful.

wade 5 years ago

Im helping a friend with wiring 3 ways, he has already run 2 wire/with ground to the switches, am i asking for trouble if we skip the ground? (use the ground for a traveler)

wilderness profile image

wilderness 5 years ago from Boise, Idaho Author

Yes, in more ways than one. Without a ground there is a potential shock hazard. You will be unable to utilize the legally required ground screw on the switch. It is not legal to do what you are proposing and any future problems (house burns down perhaps) that can traced to that wiring will result in liability to whoever did it. In many states it is illegal to sell a house with known deficiencies like this without notifying the buyer, whereupon the sale probably won't go through.

In short, don't do it. As an electrician I wouldn't do it, and if ordered to by the boss would refuse. It just isn't worth it. These codes are in place for a very good reason and need to be followed.

Good luck with your project.

wade 5 years ago

Thanks for the response, I would not have felt good about doing it that way. But, he had run the wire and had his walls up for his room addition. I thought I might be able to save him time from the setback. Again, Thanks, I see it's not worth the risk.

wilderness profile image

wilderness 5 years ago from Boise, Idaho Author

Good. It is certainly tempting to save some time and effort by cutting corners, but this is not the place. It's just too dangerous, now and in the future.

rocco 4 years ago

thank you so much,for the multiple ways,i now have better understanding of the terminology and the wiring method

wilderness profile image

wilderness 4 years ago from Boise, Idaho Author

It's actually pretty simple, isn't it? All those wires and often colors on a 3 way light switch look confusing but once you understand what is actually going on it isn't so bad.

Glad you found it useful, and thanks for the comment. It's always good to hear that I have been able to help out.

dr 4 years ago

We have an older home and had a 3 way switch between to connected fan/lights. Power comes into Switch #1 and if we use only Switch #1 to the fan/lights they work. . . .but we are trying to add the Switch #2 back in. We had a wire marked as the "T - traveler" but we cannot get the switch #2 to work again--we cannot seem to get power to it. There is not the modern 3 wire used, it was two separate double wires originally used. Can you go from the power Switch #1 to Switch #2? Would we be better off running new 3 wire to the Switch #2 or can we try to get it to work again as it is?

wilderness profile image

wilderness 4 years ago from Boise, Idaho Author

It's really hard to diagnose from a distance, but the power coming into the second switch will always come in (when the first switch has the first power cable) on a traveler.

You should have two wires marked as travelers and one as common (which will never go "hot" without that second switch wired in). If the one marked "T" never goes hot, I would suspect that it is the common, not a traveler.

You can use a volt meter, or the non contact voltage detector to trace the wires. Make sure the wires are capped and safe in the second box and turn power on. Flipping the first switch should give you two wires that go hot, then cold when the switch is flipped - these are travelers at the second switch. From your description, that leaves two wires; hook one of them to either traveler and turn that traveler hot; if the light works that wire is then it is the common and the fourth wire should be simply capped with a wire nut.

However, it is possible that earlier owners wired in a second switch that never worked properly. If you use wiring diagram #3 above, and only use two rope wire, the switches may work, but not properly. Is that possibly what has happened?

BradG 4 years ago

Do you have any suggestions for wiring 2 separate 3 way switch setups (switch-switch-light) from the same power source? I have wired it and even separated the neutrals at the second switch but still cannot get the power to switch off. Do I need to separate the grounds also?

wilderness profile image

wilderness 4 years ago from Boise, Idaho Author

First, grounds should NOT be separated. Any and all grounds in the same box are always to be tied together (exceptions can be made for special computer circuit grounds).

Let me see if I understand what you are trying to do. You have 4 three way switches and two lights. Two switches are to run light(A) and two switches are to run light(B). Power is coming from the fuse panel into the box with the first switch, (call it 1A). The same power will then go to switch (1B). From that point, the wiring is the same for each control circuit.

I am assuming here that one light is to be wired as in diagram #3. The other light, with its own two switches is also wired as in diagram #3. If this is the case, then the power in wire (black), the power in neutral (white) and the ground (bare or green) must go to both of the first two switches, one for each light. Simply run a two rope between those two switches, splice onto the power in cable, and treat each set of switches as independent.

Please let me know if this answers your question. If not, let me know either with another comment here or with an email (contact information near the top right, under my profile information). These things are difficult to answer with limited information and with just the written word, but we can get it solved.

Stefan 4 years ago

Thanks for diagram 4. No other book I looked at in Home Depot or online showed diagram 4. Once I hooked everything up, I color coded the neutral that was spliced to "hot" with black tape. I hope this was the correct action, since the neutral spliced to hot acts like hot when the appropriate switching combo is performed. Did I do right by labeling the neutral "hot" in the second switch box? Thanks.

wilderness profile image

wilderness 4 years ago from Boise, Idaho Author

@ stefan - if you spliced the white wire to the hot, it is then a hot, not a neutral, and should be colored at both ends so that no one will mistake it for an actual neutral. Black tape is fine for this purpose.

Understand that it is not the color that makes a neutral; it is where it eventually ends up in the breaker panel. Those wires or the electrons flowing in them don't know what color the insulation is. People do, though, and that is why the NEC has decreed that every neutral be white - when you spliced that white wire to the black hot it is no longer a neutral and should not be white.

Interestingly, that rule is so important that the NEC will not allow you to color a wire white. You may change the color from white to anything else (except green), but never from say, black, to white. The only exception is for #4 and larger wire, which is so large that the only use in most homes is from the street into your home.

fee 4 years ago

rewiring an old outlet-found 3 white wires to 1 side of the outlet 1 black to hot side-i can only assume that 1 of the white wires should be a hot as well,?since the outlet wont work?thanks

wilderness profile image

wilderness 4 years ago from Boise, Idaho Author

If you have three white wires to one side then they are all either neutral wires or grounds. Any hot put to the same side as either a neutral or ground will immediately blow the fuse or breaker.

With more information I might be able to offer more concrete advice. Is this old (pre 1950s) knob and tube wiring? Are there cables in the box that contain (or more) wires in each cable? Are there any wires in the box that are spliced together? Should this be a switched outlet, with one half hot all the time and one half switched? Are the wires old enough to have suffered a color change, at least to the point that black has become gray or dirty white?

So far I'm seeing a box with three neutrals and only one hot wire. I can't conceive of any application where this would be advantageous except perhaps knob and tube wiring, where there was no cabling. All normal house wiring has at least a black and a white in each cable. Or is this other than a house with the wires entering the box via a conduit (pipe)?

wilderness profile image

wilderness 4 years ago from Boise, Idaho Author

Thank you for the compliment. These switch may at first seem complex, but at the heart are actually quite simple. The best thing about them is that they are always hooked up electrically the same regardless of the physical realities of running wire.

Robert 4 years ago

I'm sorry, but these all four wiring digram looks to me the same. Those are not independent connection. If first switch is on second switch work corectly, if the first switch is off the second switch does not work. I'm not looking solution like this.

wilderness profile image

wilderness 4 years ago from Boise, Idaho Author

What you are missing is that there is no "on" or "off" with a three way switch. When the toggle is up, the common terminal is connected to one of the travelers, when the toggle is down the common terminal is connected to the other traveler. There is no "off" position. One or the other of the traveler terminals is always connected to the common terminal.

The wiring diagrams basically just show different methods of physically running the cables; in each and every case one common is connected to the incoming power and the other is connected to the light. Traveler terminals are always connected to a traveler terminal on the other switch - never to either the light or the incoming power.

amshad 3 years ago

this is useful but i need 3 way 3 swicth

wilderness profile image

wilderness 3 years ago from Boise, Idaho Author

Amshas, I'm not sure what you refer to. If you can be more specific in your needs and what you are trying to accomplish, perhaps I can help you out.

bob 3 years ago

i need to power one light from seven or eight different locations using 3 way and 4 way switches using 14/3 wire can i do that many

wilderness profile image

wilderness 3 years ago from Boise, Idaho Author

Yes, that will work fine. See the article on four way switches for wiring diagrams. Just keep adding more 4 way switches to the diagram, always between the two 3 way switches. There will be 2 three way switches, one at each end of the row of switches. One 3 way will have the incoming power and the other will have the cable feeding the light itself.

14 guage wire is fine, as long as it is being fed from a 15 amp fuse. DO NOT use 14 gauge wire on a circuit with a 20 amp breaker. is the article on 4 way switches.

phillip 3 years ago

I have a friend doing work in my bathroom which has old wiring coming from the circuit breaker. The new light fixture we're adding has a ground wire. He stated that it would be OK to twist the ground wire into the black wire. Is this correct;

wilderness profile image

wilderness 3 years ago from Boise, Idaho Author

If you put both black fixture and ground wires to the black wire from the circuit breaker the best thing that will happen is that it will blow the breaker. More likely, in residential construction, it will cause all the metal of the fixture to become "hot" whenever the light is turned on. Touch both the light and a ground source such as the sink faucet and you will be shocked.

So, it is absolutely NOT OK to put the ground wire to the black wire. If the house does not have ground wires, simply tuck the fixture ground back into the box. The primary purpose of the ground wire there is to blow the breaker if the fixture is defective somehow and the black wire is touching the metal parts of the fixture somewhere inside the fixture. As long as the fixture is in good condition (presumably a new fixture is) there will be no problem.

Jerry Leviner 2 years ago

My problem after wiring for a new light with two 3 way swithes is that if both switches are down then the light will not come on at either switch. It loses power at the non power switch! What did I do wrong?

wilderness profile image

wilderness 2 years ago from Boise, Idaho Author

It is almost certain that at one or the other of the switches the common wire has been switched with a traveler. Check at the switch where the power originates and verify that first one and then other other traveler is powered when the switch is flipped. If not, one of the travelers is interchanged with the power here.

Then verify at the other switch that the switch can transfer power, or not, regardless of which traveler is hot, to the common wire. If not, one of the wires is interchanged with the common going to the light fixture.

From your description, the problem lies with the power switch. That switch should always produce power at one of the two travelers.

Jacob 2 years ago

I have a 3 way in my hall way my 2 new motion sensors have the 3 red black and ground but the old switches have 2 black wires I know witch one is the common but with only 3 wires how do I hook up the 4th wire

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wilderness 2 years ago from Boise, Idaho Author

Doesn't sound as if your motion sensors are 3 way. Are you absolutely positive that they are? In addition, the old switches, if 3 way, had three terminals on them, plus a ground, that all had to have a wire. Two black wires is not enough - what other wires/colors are in the boxes?

Spencer 2 years ago

I have a 3 way switch that is working correctly In my basement. I want to add another switch, to make it a 4 way, in between the existing two switches. I have 12-3 run from switch to switch. The power to the lights comes out of switch one with 12-2. Is that possible without taking drywall off?

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wilderness 2 years ago from Boise, Idaho Author

You will need to install the new 4 way switch in between the two 3 way switch. In between meaning electrically, not necessarily physically. You will need a 12-3 from a 3 way, to the 4 way and on to the other 3 way.

Instructions and diagrams are available here:

donald 2 years ago

I was just looking to see if the Code called for color specific wires for the travelers and happened upon your site. I am happy to see that there are individuals out there that take the time to describe the functioning of a 3-way circuit in understandable detail as you have. Pat on the back. I have a question. What article calls for there to be a neutral in every switch box? Haven't been in "The Book" for sometime and it makes sense to me. However it would be benificial to be able to show a customer they have to pay more for a job! Thank you.

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wilderness 2 years ago from Boise, Idaho Author

Article 404.2(C) is what you're looking for. "For switches control lighting loads supplied by a grounded general purpose branch circuit, the grounded circuit conductor for the controlled lighting circuit shall be provided at the switch location"

And thanks for the pat; 3 way switches really aren't that difficult, just a little different than most people are used to thinking of for switches.

moses 12 months ago

good job

piet 7 months ago

I have a 3 light switch in 2x4 box and I want every light have a switch

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wilderness 7 months ago from Boise, Idaho Author

Piet, you will have to have a power line in that box, plus at least 3 wires going out; one to each light. It would be possible to put two of them on one 3 wire romex, though, using the black and red as switch legs (one for each light) and the neutral.

Does that answer your question?

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    Dan Harmon (wilderness)921 Followers
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    Dan has been a licensed, journey level electrician for some 17 years. He has extensive experience in most areas of the electrical trade.

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