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3 way switches

3 way switches are very handy for allowing you to switch a light or outlet from two locations. 3 way switches are more complicated than a single pole switch. They require additional wiring to make these switches function properly. You must always use two of these switches for them to work correctly. First, we need to take a look at the components of a 3 way switch then we will cover what is happening internally when you flip a 3 way switch up and down. One good thing to remember as we go on is that for a light to come on it needs the positive and the negative wire connected. This will useful later as we cover different types of wiring methods at the bottom of this page.

What the screws are for on a 3 way switchAs you can see in this diagram, a basic 3 way switch actually has 4 screws. Most of the older 3 way switches only has 3 screws. The only difference between the older and the newer switch is, the ground screw. Code changes over the years has required the addition of the ground screw for safety reasons. However, it is not needed for the correct operation of the 3 way switch. It is needed for the safe operation of this switch or any other type of switching device. The biggest help with this switch is the colors of the screw terminals. This will help us in determining how to properly connect our wires when installing this switch. Some switches are made differently from others so the colors may not match exactly what is shown here. The common screw will always be a different color from the traveler screws.



How a 3 way switch works internally

This diagram pretty much nails down exactly what is going on inside of that 3 way switch you to operate it. This diagram illustrates the internal contacts inside of the switch. These contacts are made out of an electrically conductive metal. When these contacts touch, the electricity will flow through the contacts to the proper screw and then down the wire that is attached to the screw. The traveler screw contacts are fixed in place and don't move when you operate the switch. It is the common contacts that will move from traveler to traveler when you operate the switch. We must always remember that all any switch does is cut the positive/power wire in half and it also reattaches the wire using these internal contacts. There are exceptions to this but for learning purposes we will use this rule.

how to wire a 3 way switch; 3way switch wriring diagram

This is an ideal wiring method and the most basic wiring method for a 3 way switch. There are many different ways to wire a 3 way switch and we have some additional ways listed at the bottom of this section. The ground wire is not in this diagram since it is more of a safety issue than a working issue. What we basically have here is a piece of 3 conductor cable running in between the two switches. The red and the black wires in the cable are the traveler wires. The negative/neutral/white wire just needs to always stay connected to the light. This diagram shows the red wire on the left screw and the black wire on the right. Keep in mind that it DOES NOT matter which traveler wire goes to which traveler screw. On one switch we have the power cable coming from the panel box and the other is going to the light. Knowing this, we will add the contacts into this diagram and see whether or not we can tell if the light should be on.

how 3 way switch works with electricity flowing

We have added a very light glow to this diagram to represent the electricity flowing through the wires and the contacts in the switches. As you can see the electricity stops flowing at the switch located on the right. Since the internal contact in this switch is not connecting the light to the electricity there is no way for the light to receive energy and illuminate. flipping this switch to the up position will move the contact so that the energy can travel to the light.

how a 3 way switch works wiring diagram

Now with the switch on the right, flipped to the up position, we now have a completed circuit and the electricity can make it to our light for illumination.

how 3 way switches turn on lights

The wiring method shown in these diagrams is a more commonly used method in houses that are wired today. In much older home most 3 ways are wired in a totally different manner. However, for the 3 way switch to work properly it still uses this basic principle. Here are two other methods of wiring 3 way switches.

how 3 way switch wiring works

Is this light on or off? Trace out the wires and see if you can tell. This is a method call back switching. This is still a pretty common wiring method used today as well as 40 years ago. The thing to watch for here is that white wire that attaches to your traveler screw. It is being used as a traveler wire and not being used as a neutral/negative wire. The neutral wire to your light fixture has been connected at the first box so you pretty much have an extra wire that you can make use of as a traveler. This light fixture is on.

3 way switch wiring through the light

We have heard this method called different names. What we hear the most is breaking through the light. Whatever you decide to call it, this is what it looks like. Even when we drew this we found it hard to follow. Take your mouse and start from the panel and follow the power wire all the way through this circuit. Remember the neutral is already connected, we just need to use the 3 way switches to get the power to and away from the light. You will find that this setup also has the light on.