How Does a Double-Pole Switch Work?
A double-pole switch has two connectors (poles) that can control two circuits. A double-pole, single-throw switch (DPST) turns two circuits on or off. A double-pole, double-throw switch (DPDT) manages two circuits and turns both on and off together.
Most manufacturers use the abbreviations DPST and DPDT to indicate switch types. The term pole (P) refers to the number of connections on a switch, while throw (T) refers to the number of possible positions (on or off) for a given circuit, with single (S) or double (D) referring to quantity.
The simplest switch is a single-pole, single-throw (SPST) with one input and one output controlling a single circuit. Most household light switches use SPST. The DPST switch has three connections, one input and two outputs. When there are two circuits, A and B, the DPST switch allows either circuit A or B to be on but not both circuits. The DPDT has six connectors, two inputs and four outputs that allow switching circuits A and B on or off together. These three versions comprise most of the switches used in circuits, particularly for power management. For multiple connections on a circuit, engineers may use a rotary switch, with one input and many outputs.