Dear Mr. Electrician: How do I wire four way switches? I need additional light switches to control the same light fixture from multiple locations. Are there 4-way switch wiring diagrams available?
Answer: Yes, 4-way wiring diagrams are below. You can add as many 4-ways as you want as long as you have the LINE and LOAD correctly connected on the 3-way switches. NOTE: Text links go to applicable products on Amazon.com
4-WAY SWITCH WIRING DIAGRAMS
The schematic diagram below shows how all four way switches are wired. The wiring diagram further down depicts another choice of wiring method.
In some countries the four-way is called an intermediate switch. You would just continue from one 3-way switch box with the 14/3 three conductor cable (Two colored traveler wires, a white neutral, and a bare or green 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. At the other end you connect the other 3-way switch with either the LINE or the LOAD. See the light switch wiring diagrams above and below.
Follow the switch manufacturer’s instructions and wiring diagram as the connections on the switch vary by manufacturer. Sometimes the switch wiring connection diagram is printed on the inside of the 4-way switch packaging box (See example below).
Bare or green ground wires are spliced together with a pigtail or two and then connected to the metal switch box with a 10/32 machine screw, and to the green screw on the switch.
Due to the proliferation of WiFi smart switches and electronic dimmers the National Electrical Code now requires that a neutral conductor be installed in at least one of the switch boxes. See Article 404.2(C). This is easily accomplished by bringing the power feed into the switch box instead of the ceiling light. It is not acceptable, and can be dangerous, to use the equipment grounding conductor as the neutral connection for a smart switch.
At one time there were electronic switches and dimmers that were approved to connect the neutral of the switch to the grounding conductor. That is no longer allowed. There may be some smart switches for sale that do not require a neutral conductor to operate, but their functions may be limited.
You must use electrical boxes for your light switches that are approved for the number of wires and devices that you will be installing. See article 314 in the National Electrical Code (NFPA 70) to determine what size electrical boxes you should use.
Keep in mind that each light switch will count as two wires when calculating your box fill. In addition any clamps inside of the box will count as one wire. Connectors that are outside the electrical box with only the locknut inside do not count as a wire.
An update in the 2020 National Electrical Code requires that all ceiling light electrical boxes where a ceiling fan could possibly be installed must be rated for ceiling fan support. See article 314.27(C).
Below is another method for wiring 4-way switches. The electrical switch box that contains the LINE and LOAD wires may need to be bigger than the other switch boxes, especially if there are other wires going into the switch box.
Whenever the white wire in a cable is not being used as a neutral conductor, it must be re-identified with a different color other than white, gray, or green. There is no limit as to how many 4-way switches can be used in a lighting switch circuit.
In the diagram above splices are made and a three conductor cable is installed between all the switches. The white wire needs to be re-identified as a hot conductor because it is not being used as a neutral in this installation.
I usually use blue electrical tape for re-identification, but any color besides white, gray, or green can be used. Some electricians will use a permanent marker type pen to change the color.
When 3-way switches are used, the LINE and LOAD wires can only go onto one specific switch screw terminal. It is a different color screw from the other two screw terminals.
With 4-way switches you must read the manufacturer’s instructions or wiring diagram. Sometimes there is only a switch wiring diagram printed on the inside of the 4-way switch package box. The wiring connections on 4-way switches varies between manufacturers.
It is possible to bring all of the wiring into the ceiling light electrical box and wire your 3-ways and 4-ways from there. It can get crowded with so many wires in the ceiling box so you must use a larger size electrical box to be code compliant.
Two cubic inches are required by the National Electrical Code for each #14 wire. See Tables 314.16(A) & (B). I have a diagram for all conductors in the ceiling box on my 3-way switch diagram page.
I did not include grounding conductors on the 4-way switch wiring diagrams in order to keep them simple. However each switch and metal electrical box is required to be grounded. This is commonly achieved by splicing all of the ground wires together and than adding a pigtail to them for each switch at that location.
Click here for my post on single pole light switch wiring diagrams.
My wiring diagrams for switched outlets might be useful to you.