Dear Mr. Electrician: I need to see some three-way switch wiring diagrams. I have two switches that control one light in my kitchen. I am not sure if they are 3-way switches or 2-way light switches. I find that one switch has to stay in the up position at all times just so the other switch will turn on the light. How do I diagnose and fix this?
Answer: This article has a few different three-way switch wiring diagrams and one 2-way diagram, along with some good advice. One diagram is above, the rest are below.
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Table of Contents:
- Components of Three-Way Switch Wiring
- More Three-Way Diagrams
- LINE and LOAD in the Same Switch Box
- All Wires Are in The Ceiling Electrical Box”
- United Kingdom Two-Way Switch Wiring Diagram
- Three-Way WiFi Smart Switch
- How to Identify Three-Way Switch Wires
Two-way electrical light switches and 3-way light switches are the same, they have different names according to country. One of your three-way switches may have broken down.
Shut off the electrical power for the circuit at the circuit breaker box. Due to multiple wires being hot in this particular type of switch wiring, it can be a little tricky for an amateur to diagnose which 3-way switch failed.
Assuming that the 3-way switches were wired correctly, I suggest that you change one switch. If that doesn’t fix it, then change the other one.
I take one wire off the old switch at a time and put it on the new switch, then repeat with the other wires. Please note the different color screw terminals. It’s a good idea to replace both switches simultaneously as the other one could fail soon after.
If the 3-way switches were not correctly wired, then you must be very careful to identify the LINE and LOAD wires BEFORE you disconnect the switches. LINE is the power and LOAD goes to the light or other things controlled by the 3-ways.
The LINE wire will be live (Hot) with electricity at all times regardless of the 3-way switch positions which makes it the easiest to identify. Use a voltage tester with two leads or a pigtail light socket with an incandescent or halogen light bulb.
Non-contact voltage testers may give you false readings due to the proximity of the wires on the switch. It is best to remove the suspected hot wire from the screw terminal to test it with a non-contact voltage detector.
Wear insulated electrical gloves when working with live electrical circuits.
Click here for my blog post about working around your home safely.
Do not remove all of the wires from the one three-way switch at once, and then try and figure out what each wire is. First, take notice of the color of the screw terminals on the old switch.
One screw terminal will be a different color than the other two screw terminals and will be labeled “Common” (See photo below). That screw should have a LINE or LOAD wire connected to it.
Thank you to John S. for the above photo depicting the common terminals on three-way switches. The common terminals are the ones with the different colors used for LINE and LOAD. The unlabeled brass terminal screws are for the traveler wires to get connected to.
You cannot rely entirely on the wire color coding on three-way switch wiring diagrams to determine each wire’s function in an existing 3-way switch installation. The original installers used whatever materials and wiring methods were acceptable during installation time. It is best to identify the LINE and the LOAD wires.
A white wire connected to a regular single pole switch is not a neutral.
There are existing 3-way electrical switch installations that do not follow accepted industry practice or electrical code requirements. That is why it is essential to identify the function of the wires for 3-way electrical light switches.
COMPONENTS OF THREE-WAY SWITCH WIRING
All three-way switch and 2-way switch wiring diagrams have the same basic components: Wires consisting of a LINE, a LOAD, a neutral, a pair of travelers, and two 3-way switches. If you are trying to troubleshoot a 3-way switch operation, you will need to identify the function of each wire. Do this before you disconnect any wires from the switches.
The LINE wire is usually the easiest to identify because it is always live (Hot). It should be terminated on a common copper or black screw on one of the 3-way switches. The other three-way switch will connect the LOAD wire to the common copper or black screw. A voltage tester is good for testing the live wires with neutral and/or earth ground.
Note the one black screw on each of the above three-way switches. Only the LOAD or LINE wire gets terminated on the common black screw. The green screw is only for grounding purposes and must have only one ground wire connected to it.
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It is possible to replace the switches without identifying each conductor’s function. In this case, you would remove one wire at a time and put it on the same terminal on the new switch. Take note of the color of the screw terminals on the old and the new switches. Check the rear of the old switch for the “Common” terminal.
With older wires where the color is not significantly distinguishable, I use colored electrical tape to identify the conductors. It is very helpful and makes replacement much easier the next time the switches need to be changed. I always have black, white, red, green, and blue electrical tape on my truck.
A pair of “Travelers” between each three-way switch is connected to the unlabeled brass terminals. The traveler wires are interchangeable between the two brass-colored terminal screws.
On one of the 3-way switches, a LINE or hot wire connects to the common copper or black screw terminal. On the other three-way switch, the LOAD wire (The LOAD is the wire that feeds power to the light fixture) gets connected to the common copper or black screw terminal.
Below is a simple three-way schematic that can be applied to all three-way electrical light switch connections. This is only a wiring schematic and not the method used for 3-way switch installations.
More three-way switch wiring diagrams depicting actual wiring methods are further down.
Two very old three-way switches are depicted in the photo above. The screw terminals were on the front of switches many years ago. This was unsafe to have live electrical terminals close to a metal wall plate. I have seen a few instances where the metal wall plate was coming in contact with the live terminals and creating a short circuit resulting in a tripped circuit breaker.
MORE 3-WAY DIAGRAMS
Several three-way switch wiring methods can be used, and the installer usually determines the best way for his or her purposes. In some countries, the three-way switch is called a two-way switch.
The National Electrical Code requires a neutral conductor (White wire) to be installed at most new light switch locations; however, article 404-2(C) only requires the neutral at one 3-way switch location.
The three-way switch wiring diagram depicted at the top of this post is probably the most common method for wiring three-way switches. The two-wire LINE cable goes into one switch box, and the two-wire LOAD cable goes into the other. A three-conductor cable with a grounding wire is installed between the two 3-way switch boxes.
This method is also compliant with the National Electrical Code concerning box fill and the number of wires that each electrical box is limited to having inside. Read article 314.16.
At the LINE switch box, the black wire of the two-wire LINE cable gets connected to the common copper or black screw terminal on the three-way switch. The red and black wires (Travelers) of the 3-wire cable get connected to the brass terminals on the three-way switch. It doesn’t matter which traveler goes on which brass terminal.
The white LINE neutral wire gets connected to the white wire of the 14/3 cable. At the other end, the white LOAD neutral is connected to the white wire of the 14/3 cable. At the LOAD switch box, the black wire of the two-wire LOAD cable connects to the common copper or black terminal on the three-way switch. The white LOAD wire connects to the three-wire cable’s white wire. The three-way switch connects the red and black travelers in the 3-wire cable to the brass terminals.
The above method is good because it ensures the white LINE neutral conductor is available at each switch box. In addition, this method requires only a 3-conductor cable (With ground) between the switches.
Not every existing 3-way switch installation has the same wire colors. Identifying the LINE and LOAD wires before replacing 3-way and two-way light switches. Notice which wires are connected to the common copper or black screw terminals.
LINE AND LOAD IN THE SAME SWITCH BOX
A variation of the above three-way and 2-Way switch wiring is to bring all cables into one wall switch box, as depicted in the diagram below, and branch off from there to each switch and light fixture.
The LINE and LOAD are brought into one 3-way switch electrical box. From there, a 3-wire cable (2 travelers, a ground, and the re-identified white wire) or a conduit would need to be installed over to the second 3-way switch.
Whenever the white wire is used as something other than the neutral conductor, it must be changed to a different color. This is accomplished with colored electrical tape or a permanent ink marker pen.
At the second 3-way switch, the black wire would be connected to the switch’s common copper or black screw terminal.
The bare or green wire is connected to the metal switch box with a 10/32 machine screw and onto the green screw on the 3-way switch. The bare or green grounding conductor is not shown in these wiring diagrams to keep them simple.
Click here to see my blog post about outlet and switch grounding.
The electrical box must be big enough to accommodate the number of wires. See Article 314.16 in the National Electrical Code (NFPA 70) for electrical box space requirements.
In the above diagram, the white wire must be re-identified with a different color at each switch location. The white wire between switches is not being used as a neutral; it is a traveler and cannot be white.
Use colored electrical tape other than red or black or a permanent ink marker pen to change the wire color. The photo below shows the LINE and LOAD in the same switch box.
In the photo above, the green arrow points to the LINE hot wire connected to the black wire of the 14/3 cable going to the other 3-way switch. The blue arrow points to the LOAD wire, which will be connected to the common black or red-colored terminal on the 3-way light switch to be installed in this box.
The red and blue wires in this installation are the travelers. This was added to an existing installation that had only one single-pole wall switch at the top of the basement stairs for the basement lights. The homeowner wanted an additional switch in the basement.
The photo below shows the wiring at the other 3-Way location, which was a single-pole switch initially.
The black hot wire in the electrical box above is connected at the other end to the black LINE wire and gets connected to the common black or red screw on the 3-way switch. The white wire has been taped with blue electrical tape to show that it is not a neutral conductor but a traveler. The red wire is the other traveler. The travelers connect to the two brass screw terminals on the 3-way switch.
When a white wire is being used as a traveler, it needs to have its color changed according to Article 310.110(C). Any color but white, gray, or green can be used. The extra clamp at the top of this switch box needs to be removed as it counts as one additional wire (Article 314.16(B)(2).
At the first switch box, the black wire that was run to the second 3-way switch can be connected to either the black LOAD wire or the black LINE wire. The black LINE wire or LOAD wire that is not connected to the second 3-way switch; gets connected to the common copper or black terminal of the first 3-way switch.
The LINE and LOAD white neutral wires should be spliced together. The traveler wires from the second switch get connected to the same two brass terminals on the first switch.
The ground wires should all be joined together, and one or two pigtails connected from that bunch should be connected to the metal box with a 10/32 machine screw and the green screw terminal on the 3-way switch.
ALL WIRES IN THE CEILING BOX
Another example of an alternative 3-way wiring method is bringing all cables into the ceiling light fixture electrical box. From there, a three-conductor cable or a conduit would need to be installed to one of the 3-way switch locations. A four-conductor cable with a grounding conductor; or a conduit would need to be installed to the other 3-way switch location as required by code to have a white neutral conductor in one of the switch boxes.
A larger ceiling electrical box would be needed to accommodate all of the wires in this type of 3-way switch installation. A minimum of 24 cubic inches is required if #14 wire is used. See Tables 314.16(A) & (B). Two cubic inches are required for each #14 wire.
An update in the 2020 National Electrical Code requires that all ceiling light electrical boxes where a ceiling fan could be installed must be rated for ceiling fan support. See article 314.27(C).
At each switch in the above 3-way switch wiring diagram, the black wire gets connected to the common copper or black screw. In the ceiling light fixture electrical box, one black wire from a 3-way switch gets connected to the black LOAD wire on the light fixture. The black wire from the other 3-way gets connected to the LINE black wire. The LINE white neutral wire gets connected to the light fixture.
The travelers in the ceiling light junction box get spliced color to color. All of the grounding conductors are connected, including the grounding pigtails from the metal box and the light fixture. The ceiling electrical junction box must be extra-large to fit all the wires. Take note of the white neutral wire required to be in one of the switch boxes.
UNITED KINGDOM TWO-WAY-SWITCH DIAGRAM
In the United Kingdom, some electricians use an alternative method for wiring two-way switches, as depicted in the above wiring diagram. Two-way switches and three-way switches operate the same way and have the same connection points; they just have different names in the UK, which are Common, L1, and L2.
The above switch wiring diagram shows a different wire color coding than what is used in the USA. In this wiring configuration, the Common terminals on each 2-way switch are connected with one wire. The LINE wire is connected to the L1 terminal, and the LOAD wire is connected to the L2 terminal.
If you wanted to add more switches, you would install four-way or intermediate switches in Europe, which are wired to the L1 and L2 wires. The intermediate switches are wired in between the two-way switches. Using a three-core cable, the Common wire going to the 2-way switches just passes through each intermediate switch electrical box. Colored electrical tape is used to re-identify the wires.
These diagrams do not show the ground wires to save space and make for easy viewing. However, all ground wires would be joined during the installation, and a pigtail for each switch would be added. All metal electrical boxes need grounding with a separate grounding pigtail hooked around a 10/32 machine screw in the back of the box.
Changing a 3-way switch to a WiFi smart switch can be tricky. You will need a white neutral conductor to power the smart switch. You cannot use the bare or green grounding conductor instead of a neutral conductor. In addition, some changes may need to be made at the other 3-way switch in the circuit.
A white wire connected to a standard wall switch is not a neutral conductor.
The LOAD and one traveler will most likely need to be connected while the other traveler is capped with a wire connector. Every smart switch will be different, and you must follow the manufacturer’s installation instructions.
Before buying a smart switch, I suggest you check the manufacturer’s website for the installation instructions. Read the instructions before purchasing the smart switch. Read my instructions below for identifying wires.
HOW TO IDENTIFY 3-WAY SWITCH WIRES
One piece of advice my dad gave me for troubleshooting 3-way switches, which I still use now, is, “Identify the LINE and the LOAD wires first.”
LINE is easy because it is your power source and is always live. Once you have your LINE hot wire, the LINE neutral is in the same cable. The LOAD can be a little trickier to find, but using the LINE hot wire and a pigtail lamp socket with an incandescent light bulb, it is easy to test each wire without blowing the circuit breaker.
When identifying wires, it is best if they are disconnected from the switch. Mark them with numbers and take a picture of them before removing the wires from the screw terminals.
Use a large paper clip end or a tiny eyeglass screwdriver to release wires inserted into the holes on switches and outlets.
The neutrals need to be connected for this method to work, so you connect one white wire at a time to the LINE neutral and then test each other wire with the pigtail light socket connected to the hot LINE wire, and each one of the other wires until you get a dim glow in the light bulb or the ceiling lights. A dim glow means that the pigtail bulb is in series with the lighting LOAD.
When testing for outlets controlled by three-way switches, plug a lamp with an incandescent or halogen bulb into the outlet. I sometimes use a plug-in outlet to light socket adapter or a pigtail socket.
A pigtail light socket is better because a multimeter can give misleading or erroneous readings. A light bulb is either off, brightly lit, or dimly lit. When it is dimly lit, it is in series with another load. Brightly lit means that it is connected to power.
It is best to use an incandescent light bulb, though they are difficult to find these days. Appliance bulbs are still incandescent, I think. A halogen bulb will work also, but they get very hot and are dangerous if they break while in use. LED light bulbs and compact fluorescent bulbs may not work as well due to the electronic circuitry in each.
My three-way and four-way switch diagrams are available as stickers for your toolbox, hard hat, foreman’s backside, or lunch box, so they are handy when needed. Use this link: http://redbubbleus.sjv.io/0Jn05V
Some more information on UK 2-way switch wiring
For single pole light switch wiring diagrams, see my post here.
You might find my post depicting 4-way switch wiring diagrams useful.
If you plan to install a ceiling fan, visit my post depicting ceiling fan wiring diagrams for additional guidance.
To wire wall switches to control electrical outlets, see my post here.
My three-way switch wiring diagrams are available as stickers from RedBubble.
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