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How to Wire a 4 Way Switch when Power and Light Wires Run to the Same Electrical Box

Do you know how to wire a 4 way switch when all the wires seem to go to the same electrical box?  This situation can confuse some homeowners who are faced with more complicated 4-way wiring.  Hopefully the diagram below helps illustrate how the circuit works. In this setup, a white conductor (typically used for neutral) is taped on each end to designate the wire as a hot conductor rather than the neutral.

 Four-way switches are used to control power to a light from three or more different locations.  You must purchase switches labeled as 4-way switches rather than 3-way or normal light switches.  4-way switches can be quickly identified by the 4 screw terminals (in addition to the green/gnd screw terminal).  Two of the terminals are brass and labeled "input", the other two are black and labeled "output".  It is very important to pay attention to these as shown in the 4-way switch diagram.

When wiring a 4 way switch circuit as shown below, you will use two 3-way switches and one 4-way switch.  If you wanted to add a fourth switch to the circuit you would need another 4-way switch wired in the middle in the same way as the first 4-way switch.  You might ask, how can I wire a 4 way switch with regular light switches, or all 3 way switches, or all 4 ways switches?  The answer is you can not.  You must have a 3 way (3 terminal) switch on each end of the series and then a 4-way (4 terminal) switch in the center.  If you don't have the right switches you need to get the right switches rather than wasting time attempting to make it work.  I only say that because I've seen people try to figure out ways to make it work, using the wrong switches, and they end up with switches that have to be in certain positions for other switches to work and it's a huge mess to straighten out.


4-Way Switch Diagram (Power and Light into Same Box) - (pdf, 33kb)


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