Dear Mr. Electrician: How do I wire additional switches to control the same light fixture from multiple locations.
Answer: If more than two switch locations are wanted, one or more four-way switches would need to be installed in between two 3-way switches. 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 (Follow the switch manufacturer’s instructions). Ground wires are spliced together and bonded to the metal switch box and to the green screw on the switch. At the other end you connect the other 3-way switch with either the LINE or the LOAD.
You must use electrical boxes for your 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 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 do not count.
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, 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.
When 3-way switches are used, the LINE and LOAD wires can only go onto one specific switch screw terminal. It is usually 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 wiring diagram printed on the inside of the 4-way switch package box. The wiring of 4-way switches varies between manufacturers.
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.
My post depicting 3-way switch wiring diagrams will be helpful to you.