How does a double-pole switch work?


Quick Answer

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.

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Full Answer

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.

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