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A 4-way switch wiring option is fairly complex. Power enters the first light fixture box instead of the first 3-way switch box. This wiring configuration is no longer allowed as of the 2011 NEC if a neutral wire is not present in the switch boxes.
In the diagram below, a 2-wire NM cable supplies line voltage and neutral from the panel to the first light fixture box on the left. The line (black) wire eventually connects to the common terminal of the first 3-way switch. The neutral (white) wire connects to the light fixture(s) and the white wire(s) of the NM cable(s) that connect between the light fixture boxes. This neutral wire terminates at the last light fixture box and does not travel through any switch boxes.
A 2-wire NM connects the last light fixture box to the first 3-way switch box. The black wire connects to the common terminal of the first 3-way switch. The white wire (line switched) connects the white wires of sequential NM traveler cables together and eventually connects to the common terminal of the second 3-way switch. These wires should have black tape on both ends to indicate line instead of neutral.
A 3-wire NM connects the traveler terminals of the first 3-way switch and the first 4-way switch. A 3-wire NM connects the traveler terminals of the first 4-way switch and the second 4-way switch, and so on. A 3-wire NM connects the traveler terminals of the last 4-way switch and the second 3-way switch. The traveler wires are interchangeable on each switch.
The common terminal of the second 3-way switch supplies line voltage switched from the second 3-way switch through the switch boxes and back to the light fixtures using the NM white wire with black tape on each end.
Diagrams shown on this page are simplified for clarity. Electrical outlet boxes can have numerous NM cables going in and out. See Actual Switch Box Wiring Diagram.
Ground connection diagram is shown separately.
4-Way Switch Wiring Option Diagram
4-Way Switch Wiring Option
