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Replacing a three way switch How To

Replacing a three way or four way switch is easy. Troubleshooting 3 way switch circuit wiring problems can be very intimidating and time consuming.

Do not try to install a new 3-way switch by copying the physical layout of the old one, for example red wire top left and black wire bottom left.
Switch manufacturers have different physical locations for the common terminal, even for different styles of their brand. To make matters worse the drawing on the wiring diagram supplied with the switch usually does not match the actual layout of the switch.

A basic 3-way and 4-way switch wiring diagram is shown below

There are 28 combinations for connecting the wires at two 3 way switches, of which only four of them will work.
The Switch Wizard tester will unscramble your mixed up 3 way switch wiring.
If you have already changed the switch and now it don't work then the wiring is mixed up. Checkout the Switch Wizard 3 way electrical switch wiring tester to see how fast and easy it can be to unscramble it.

Here are some important tips:
When light fixtures are controlled from two or more locations the wiring is called a three way switch circuit. 3-way switches have three wires connected to them ( not including green or bare ground ), one common and two travelers. 3 way switches operate in pairs. If there are only two switches for the same light(s) then they will both be 3-way switches. If there are more than two then there are still only two 3-ways and the others are 4-way switches. 4-ways will have four wires connected to them ( not including the ground ), two traveler pairs. 3-way and 4-way switches do not have ON and OFF markings on the toggle handle.

3 way switch wiring diagram


To successfully replace the switches you need to know which wire is the common at each 3-way switch location. You also need to know which wires are traveler pairs at the 4-way switches.
Also you cannot go by the color of the insulation on the wire.
Yes there is a correct color scheme for 3-way circuit house wiring but it may or may not have been followed when the original wiring was done.

Before disconnecting the wires from the 3-way switches mark the wire connected to the odd colored screw on the switch ( not the green one ). The screw is usually black or copper colored. On most switches the word "common" is stamped into the plastic next to the terminal.
On 4-way switches mark two of the wires closest to one end of the switch (not the ground wire of course). These two screws will be a different color than the other two.
Now disconnect the wires from the switches. If the wires are pushed in the back of the switch push a small screwdriver into the rectangular slot next to the wire and pull on the wire. If it won,t come out just cut it off as close as possible to the switch and strip 5/8 inch of the insulation off.
Now connect the new three-way switches. The wire that came off the common terminal of the 3-way switch must go back on the common terminal of the new switch. The other two wires known as travelers connect to the remaining two terminals, one wire to each terminal and it doesn't matter which one to which.
Install a 4-way switch by connecting the two wires you marked to the two terminal screws that are the same color. They are usually closest to the ends and on opposite sides, not side by side and not green. The remaining two wires connect to the other two terminals.
If there are any white wires connected to the switch terminals please re identify them with black tape or paint to distinguish them from a white neutral wire, an electrical code issue.
When you mount the switches into the elctrical box be careful the ground wire does not loop up and touch any of the switch terminals.

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