A 3-way duplex switch contains two 3-way switches on one body. Two of the common terminals are connected together with a removable metal tab. These terminals are usually connected to line voltage and can be black or bronze color depending on the manufacturer. This tab is removed to isolate the tabs from each other.
3-Way Duplex Switch Diagrams
Metal tab connects the two common terminals together.
Common terminals black or bronze color.
Metal tab removed to isolate the common terminals.
Duplex 3-way switch with conventional 3-way switches
Duplex switch common terminals connect to one line. When duplex switch metal tab is removed, each common terminal connect can connect to a different line.
Ceiling fan diagram using duplex and conventional 3-way switches