Three way switch: 3-Way Switch Wiring – Electrical 101

Three-Way Lights – How Three-Way Switches Work

To create lights that operate with two separate switches, the electrician uses two special pieces of equipment in the circuit:

  • Special switches known as three-way switches
  • Special wire that has an extra red insulated wire along with the black and white wires within the sheath

A normal switch has two terminals that are either connected or disconnected. A three-way switch has three terminals, and the switch connects the first terminal to either the second or the third terminal, as shown here:


You use two three-way switches to control the light, and wire it up as shown below:


In this diagram, a normal piece of wire comes from the fuse panel to the first three-way switch. The black “hot” wire enters the switch on the left. Three-way wire(which includes red, black and white wires) runs from the switch on the left to the switch on the right, with the white wire carrying ground and the red and black wires carrying the output from terminals in the left switch. Normal sheathed cable runs from the right switch to the light.


Assume that, with the switch up, terminals 1 and 3 are connected as shown above. If the switch is down, then terminals 2 and 3 are connected. You can see (if you trace through the wires and the switches) that in the previous figure, the light is off. You can also see that if you flip either switch, the light will turn on. And if you flip either switch again, the light will turn off. It is actually a very simple arrangement once you see it all exposed like this!

There are several other ways to wire three-way switches to a light. For example, the power from the fuse box could come in at the light fixture and there could be two switches in series running from there. Or power can enter at the fixture and then two switches can be arranged in parallel from the light.

If you are trying to understand how a set of switches are wired in your house, using an ohmmeter or a continuity detector is the only way to reverse-engineer what the electrician has done (make sure you turn the power off at the fuse panel before doing anything with electrical wiring). The great thing is that, if you know the basic idea behind three-way switches and three-way wiring, it’s really easy to figure it out. And if you simply want to understand what’s going on to satisfy your own curiosity, well, now you know!

For more information on three-way switches and related topics, check out the links below.


Related HowStuffWorks Articles

More Great Links

  • HandymanWire: Wiring a 3-Way or 4-Way Switch
  • The Magic of a “Three Way” Switch
  • Three-Way Switch Circuits
  • The Three-Way Switch How-To

Cite This!

Please copy/paste the following text to properly cite this article:

Marshall Brain
“How Three-Way Switches Work”
1 April 2000. <>
30 June 2023

3-way or Three-Way Switch Maintenance and Troubleshooting

This scene is repeated in hundreds… maybe thousands of homes every
evening. ..

A long day… really tired… and all you want to do is go upstairs to lie
down. Oh, how her feet hurt! The upstairs is dark, and as she flips the switch
at the bottom of the stairs, she howls… as nothing happens! The dang 3-way
switch isn’t working. So, to turn the light on, she carefully negotiates the
stairs to the top, and flips on the switch. That’s just not the way it’s
supposed to be, is it?

3-way circuits can be a formidable opponent.

Countless homes across the country are plagued by miswired 3-way circuits
causing not only inconvenience but a genuine safety hazard. They are very simple
in function, yet ingenious in design. It only takes a few minutes, a little
patience, and a healthy respect for electricity to get this job done right!

Right off the bat, I need to tell you that this is not an article on
designing 3-way circuits… it’s strictly regarding repair. 3-way and four-way
circuits can be confusing to design, and even more confusing to install.
However, intimate knowledge of circuit design is not really necessary for this
repair… as long as the circuit was wired correctly in the first place!

What is a 3-way circuit?

A 3-way circuit is a lighting circuit that allows one light fixture to be
controlled by two wall switches in different locations. Stairwells, hallways,
and large rooms with multiple access are all candidates for 3-way circuits.

There are also four-way, five-way, and a gazillion-way circuits! These
circuits are designed using switches known as 4-way switches between the two
3-way switches. For example, a circuit with 4 switches controlling one
fixture… not uncommon in large rooms with multiple access points… there are
two 3-way switches and two 4-way switches.

The heart of a 3-way circuit is the 3-way switch. Unlike a common wall
switch, the 3-way switch has three active terminals (plus a ground in
up-to-date installations). Only one of them is important to identify for
the purposes of replacement. .. the common

Though our graphic (left) shows the common terminal in a certain position, the
fact is that it could be any terminal on your individual switch. 

Sometimes the toughest thing to do is identify it. If there is no labeling on the
switch, there may be a different color fastening screw used for the common
terminal… may be black (for a newer switch) or “differently” colored than the two traveler terminals.

What is the common terminal?

The common terminal is one of three electrically active terminals on a 3-way
switch (not including the ground terminal that is located on the metal frame of
the mounting ears).  The common terminal is the “bridge” between the power
supply and the load (typically a light fixture).  With this in mind, the
wire that attaches to the common terminal is either (1) a hot wire from the main
board or (2) leads to the load (fixture).

What are the travelers?

Travelers are two wires connecting the two 3-way switches together.  
Referring to the graphic (above), the two traveler terminals on one 3-way
switch are connected to the two traveler terminals on the other 3-way switch by
the two traveler wires. Either traveler wire can
be connected to either traveler terminal… it doesn’t matter!

Confused?  Need a picture?

X-Ray View of a typical 3-way circuit…

The above graphic courtesy Leviton
Manufacturing Company

NOTE: If your 3-way circuit uses an outlet or outlets
instead of light fixtures, you might get confused with the wiring if the outlets
are “split”… one of the plugs is always on and the other is controlled by the
wall switch.

Replacing a defective 3-way switch…

(The graphic above will help you understand the text below… and visa

NH’s rule for replacing defective 3-way switches is to
! There is a common sense
reason for this. If one switch has failed, how much longer can the other one
last? Besides, it’s a chore to determine which of the two switches has become
defective. So in the long run it behooves you to spend a few extra dollars now
for a reward that will last for years or even decades!

Once you locate the common terminal, replacement of a defective switch is

1) Attach the common wire to the common terminal on the new switch.
The remaining two insulated wires are then attached to the remaining traveler
terminals.  Depending on the wiring in your home, the bare ground wire is
attached to the ground terminal on the metal frame of the switch’s mounting
ears. If you wiring is up to modern codes, the common wire will be black
and the travelers will be white

2) Screw the switches back into their boxes, put the switch plate covers on, and
turn the power on to test the switches.
Amazing, isn’t it!  You should now be able to turn your light on and off
from either switch.

What… it doesn’t work? No luck? Well, you must not have connected the
common wire to the common terminal! So now your assignment is to identify the
common wire.

Identifying the common wires…

Sometimes, a 3-way circuit doesn’t work because someone tried to replace a
defective switch and did not properly connect the wires.

Sometimes, one of the switches has become defective.

The following method will address both problems
at once.  The steps I am going to describe may not be the most time-efficient way
to troubleshoot a 3-way circuit. Laid out with y”all handyman-electricians
in mind, it allows you to identify the common wires in both switch boxes with no
possibility of error! You will need a multimeter to test voltage and continuity
in the circuit.

1) Turn off the power to the circuit at the main panel. Disconnect all three
wires (or four, if the outlet is grounded) from both switches. Separate the
wires so that they are as far away from each other as possible.

2) Turn the power back on. Now, using your multimeter, you are going to
determine which of the three colored wires is the HOT
wire. There should be only one HOT wire in one of the two switch boxes. This is the common wire for that
box. Set your multimeter to at least 110 volts. Hold one of the probes on a
known ground, such as a metal outlet box or a bare ground wire. Touch the other
probe to the colored wires, one by one. The wire that registers voltage is the HOT
wire, and the common wire for this box.

NOTE:  It is wise to also test the three colored wires in the other box for voltage
also, if you haven’t already. There should not be any, but with the strange
wiring I have seen over the years, it is worth taking a minute to do this. Using
a voltage tester, touch one probe to a known ground (metal outlet box or
bare ground wire) and the other probe to each wire.  You should not
get a voltage reading.  If
you do find voltage, this means that this switch is meant to control another
appliance, light, or outlet. Perhaps you are checking the wrong switch? 


Once you have finished testing for

HOT wires, turn the POWER OFF! You will not need power again until the switches are

3) Install the first 3-way switch in the box with the
HOT wire, attaching the
HOT wire to the common terminal of
the switch.  Attach the other two wires, the travelers, to the other two
terminals of the switch.  If there is a bare ground wire, attach that to
the ground lug of the switch.

4) Go to the other box (without a HOT wire). Set your multimeter to infinite resistance or to “continuity”. Touch one of the probes of the
multimeter to a known ground, such as the metal outlet box or bare ground wire.
Touch the other probe each of the three wires. Only one of them will register
resistance or, if you have a continuity tester, will cause a “beep”. You have
identified the common wire for this box.

5) As with the first box, connect the common wire to the common terminal on the new
switch. Connect the other two wires to the TRAVELER terminals, and the
ground wire if applicable.

Screw the switches back into their boxes, put the switch plate covers on, and
turn the power on to test the switches.

NOTE:  If your 3-way circuit uses an
outlet or outlets
instead of light fixtures, you might get confused with the wiring if the outlets
are “split”… one of the plugs is always on and the other is controlled by the
wall switch. 

“hot” side, there is a metal strip that connects the two screws.  If this
strip is broken, then the two plugs are independent of each other.  There
will be black (hot) wires attached to each screw terminal, though this alone
does not indicate that the outlet is split.  It may mean that the outlet is
connected to another outlet.  IF THE METAL STRIP HAS BEEN BROKEN OFF, YOU


The first two graphics show the metal strip or tab.  The third and
fourth graphics show how the tab is easily removed with a set of needle-nose
pliers.  Once the tab is removed, the upper and lower outlet plugs are
independent so one can be, for example, controlled by a wall switch while the
other is always on.

If you have a split outlet, follow the same 3-way switch troubleshooting as
with a light fixture EXCEPT you will need to determine which outlet is always

After disconnecting all the wires from the switches and from the switched
outlet(s), turn the power on and test the wiring at the outlet.  The hot
wire leading from the 3-way switch circuit will have no power, since all power
must travel through the switches.

If one of the black (hot) wires does have power, then that is the wire for
the “always on” plug.  Turn off the power and mark it so you don’t confuse
it with the 3-way circuit wires.  Enjoy!!

Return to Electrical Article List

EKF Three-position switch Basic tps-2-32

EKF Three-position switch Basic tps-2-32

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EKF Three position switch Basic tps-2-32

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Three position switches EKF Basic are mechanical switching devices.

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