Three Way Light Switch Wiring Diagram

3 way and 2 way light switch wiring with the line and load in the same switch box.. The larger square box was used to accommodate the extra wires. In this instance the white wire in the 3 conductor cable was reidentified with blue electrical tape to indicate that it is not a neutral conductor. The line hot wire from the 2 conductor feed cable is spliced through to go to the 3 way switch at the other end of the room.
3-way light switch wiring above with the LINE and LOAD in the same switch box. The blue arrow points to the black LOAD wire. The red and blue wires are called travelers. The larger square electrical box was used to accommodate the extra wires. A 4" square switch ring will be added before finish. In this instance the white wire in the 14/3 Type NM four conductor cable was re-identified with blue electrical tape to indicate that it is not a neutral conductor. The black LINE hot wire from the 14/2 NM feed cable is spliced onto the black wire in the 14/3 cable to go to another 3 way switch at the other end of the room. The white LINE neutral wire is spliced to the white LOAD neutral wire. Note the green 10/32 grounding screw where the box gets grounded. The same wiring schematic is used for two way light switch installations.

Dear Mr. Electrician: 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: Two way electrical light switches and 3 way light switches are the same thing, they just have different names according to country.  I am guessing that one of the three-way electrical light switches broke down.  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.  I suggest that you change one switch.  If that doesn’t fix it, then change the other one.  It’s a good idea to replace both switches at the same time anyway as the other one could fail soon after.  Be very careful to identify the LINE and LOAD wires BEFORE you disconnect the switches. 

You cannot rely on a color coded schematic wiring diagram to figure out what each wire’s function is.  The original installers used whatever materials and wiring methods were acceptable at the time of installation.  Of course there are plenty of two way and 3 way  electrical switch installations that do not follow any acceptable industry practice or electrical code requirements.  That is why it is important to identify the function of the wires for two way and 3 way electrical light switches.  The LINE wire is usually the easiest to identify because it is hot at all times.  It should be terminated on a copper or black screw on one of the 3-way switches.  The other three way switch will have the LOAD wire connected to the copper or black screw.  A voltage tester such as a “Wiggy” is good for testing the live wires with neutral and/or earth ground.

It is possible to simply replace the switches without having to identify the function of each conductor.  In this case you would just take one wire off of the old switch 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.  On older wires where the color is not very 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.

All three-way switch and 2 way switch wiring has 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, then you will need to identify the function of each wire.  Try to do this before you disconnect any wires from the switches.  Note the colors of the screw terminals on the existing 3-way switches.  The dark or red color screw is the most important to get right.

Between each three-way switch or 4-way switch is a pair of “Travelers” which are connected to the common terminals.  On one of the 3-way switches a LINE or hot wire gets connected to the 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 copper or black screw terminal.

Below is a simple schematic diagram that can be applied to all three-way electrical light switch connections.  Please note that this is only a wiring schematic and not the actual wiring method used for 3 way switch installations.

A three way and two way light switch wiring diagram. No matter where the conductors are located in the circuit, they always get connected like this.
No matter where the switch boxes are on the wall or the light fixtures on the ceiling, or where all of the cables are terminated, the conductors for a 3-way and 2-way light switch always get connected like above. Please note that this is only a schematic diagram. The actual installation of the wiring is different.

There are several three-way switch wiring methods that can be used and it is usually the installer that determines what is the best way for his or her purposes.  The “National Electrical Code” requires that a neutral conductor (White wire) be installed at most light switch locations (Article 404-2(C).  

I think that the most common method used to wire a set of 3-way switches is to bring the two wire LINE cable into one switch box and bring the two wire LOAD cable into the other switch box.  A  three conductor cable with a ground is then installed between the two 3-way switch boxes. 

At the LINE switch box, the black wire of the two wire LINE cable gets connected to the 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 common terminals on the three-way switch.  It doesn’t matter which traveler goes on which common terminal. 

The white LINE neutral wire gets spliced to the white wire of the 14/3 cable.  At the other end the white LOAD neutral gets spliced to the white wire of the 3 wire cable.  If 4-way switches were added in-between the two 3-way’s, the travelers would be attached to the 4-way switch according to the manufacturer’s diagram, and the white wire just gets spliced through.

At the LOAD switch box, the black wire of the two wire LOAD cable gets connected to the copper or black terminal on the three way switch.  The white LOAD wire gets connected to the white wire of the three wire cable.  The red and black travelers in the 3 wire cable get connected to the common terminals on the three-way switch.

The above method is good because it ensures that the white LINE neutral conductor is available at each switch box as required by the “National Electrical Code”  In addition this method requires only an additional 3 wire cable (With ground) between the switches.

Please note that not every existing 3-way switch installation has the same wire colors.  It is important to identify the LINE and LOAD wires before replacing 3-way and two way light switches.  Note which wires are connected to the copper or black screw terminals.

Three way and two way light switch wiring with the line and load in the same 4" square box. The green arrow points to the line hot wire connected to black wire of the 3 conductor cable which is going to the other 3 way switch somewhere. The blue arrow points to the load wire which will be connected onto the odd colored terminal on the 3 way switch. The red and blue wires are the travelers which.
Three way switch wiring with the LINE and LOAD in the same 4″ square box.  The green arrow points to the LINE hot wire connected to black wire of the 14/3 cable which is going to the other 3 way switch.  The blue arrow points to the LOAD wire which will be connected onto the odd colored terminal on the 3 way light switch.  The red and blue wires in this installation are the travelers. The same wiring is also used for two way light switches.

Another variation of three-way switch wiring is to bring all of the cables into one box as in the photo above, and branch off from there to each switch and light fixture.  For example, the LINE and LOAD are brought into one 3-way wall switch electrical box.  From there a 4 conductor cable (2 travelers, a ground, and the LINE or the LOAD) or a conduit would need to be installed over to the second 3-way switch.  At the second 3-way switch, the black wire would be connected on the copper or black screw terminal on the switch.  The bare or green wire is bonded to the metal switch box and onto the green screw on the 3-way switch.  See the next photo for the other 3 way switch.

Three way and two way switch wiring with no load or line feed entering the switch box. The hot wire is spliced at the other end onto the black wire. The white wire on the 14/3 cable 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.
Three way switch wiring with no LOAD and no LINE feed.  The hot wire is spliced at the other end onto the black wire. The white wire on the 14/3 cable 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 extra clamp at the top of the switch box needs to be removed as it counts as one additional wire (Article 314.16(B)(2). The same wiring method is also used for two way switch wiring.

The remaining colors will be used as the travelers and get connected to the common screw terminals.  When a white wire is being used as a traveler, it needs to have its color changed.  I sometimes use blue electrical tape to differentiate it from other wires.  Article 310.110(C).

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 onto the 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 common terminals on the first switch.  The ground wires should all be spliced together and one or two pigtails connected from that bunch should be connected to the metal box with a 10/32 screw and to the green screw terminal on the 3-way switch.

Still another example of an alternative 3-way wiring method is to bring all of the cables into the ceiling light fixture electrical box.  From there a four conductor cable or a conduit would need to be installed to one of the 3-way switch locations.  A five conductor cable or conduit would need to be installed to the other 3 way switch location as required by code to have a white neutral conductor at the switch.  Please note that a larger ceiling electrical box would be needed to accommodate all of the  wires in this particular 3-way switch installation.  A minimum of 24 cubic inches is required if #14 wire is used.  See Tables 314.16(A) & (B).

At each switch the black wire gets connected to the copper or black screw.  In the ceiling light fixture electrical box, one black from a 3-way switch gets connected to the black 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.  In the light fixture box, the travelers get spliced through color to color.  The grounds are connected together, to the metal box, and also to the light fixture.

If more than two switch locations are wanted, a four-way switch would need to be installed in between the 3-way switches.  You would just continue from one three-way switch box with the 14/3 four conductor cable (Two travelers, a neutral, and a ground wire) in and out of each four-way switch box.  The white wires get spliced through.  The red and black wires are connected to the four way switches (Follow the switch manufacturer’s directions).  Ground wires are spliced together and bonded to the metal switch box and to the green screw on the switch.  At the other end you connect the other 3-way switch with either the LINE or LOAD.  See the diagram below.

Four way light switch wiring diagram.
Four way switch wiring diagram.  A four way switch is added when there are more than two switch locations operating the same light. This wiring schematic is also used when installing a 4-way switch with 2-way light switches.