A three-way switch is which type of switch?

• A. SPDT
• B. SPST
• C. DPDT
• D. Four-way

Answer: (A)

A three-way switch is SPDT, which stands for single pole, double throw. This means the switch has one common terminal (the pole) that can connect to either of two terminals (the throws). In a typical setup, two SPDT switches control one light: each switch selects which traveler path is connected to the common, so flipping either switch changes the circuit path and whether the light is on or off. This is different from SPST, which is just a simple on/off with one path; DPDT, which has two poles; and a four-way switch, which is used between two SPDT switches to allow control from more than two locations. The key idea is that a three-way switch provides a single input that can be directed to one of two outputs, enabling two-location control of a single load.