A duplex switch contains two switches on one body. They come in single pole and 3-way. 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.
Duplex switches can replace a single switch without expanding the switch box. They can be used for ceiling fans where one switch controls the fan and the other switch controls the light kit.
Single Pole Duplex Switches
A single pole duplex switch contains two single pole switches.
Single Pole Duplex Switch Diagrams
Metal tab connects line voltage together
Common terminals black or bronze color
Metal tab removed to isolate common terminals
Duplex switch common terminals connect to one line
Duplex switch each common terminal connect to a different line