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Switches are classified by the number of circuits they control (poles) and the number of positions they switch between (throws)

Fact L1Foundations E · Modular, Eurorack, grooveboxes & dawless

Switch nomenclature uses two dimensions: poles (how many independent circuits are switched simultaneously) and throws (how many positions each circuit can connect to). Single Pole Single Throw (SPST) turns one circuit on or off. Single Pole Double Throw (SPDT) routes one circuit to one of two destinations. Double Pole Double Throw (DPDT) routes two independent circuits simultaneously. The additional categories are Normally Open (NO — circuit open at rest, closed when operated), Normally Closed (NC — circuit closed at rest, opens when operated), and Common (C — the shared terminal). Momentary switches return to their default position when released; latching switches stay in position. This nomenclature is universal across all switch types: toggle, pushbutton, slide, rotary, relay.

Examples

A SPDT toggle on a guitar routes the pickup to one of two amp channels. A DPDT footswitch wired as a true-bypass routes both the signal path and any indicator LED simultaneously.

Assessment

What is the difference between SP and DP switches? Draw the circuit symbols for SPST, SPDT, and DPDT switches and label NO, NC, and C terminals.

Sources

“Number of Poles Sometimes a single handle or button can switch two or more separate circuits simultane- ously (think of the huge double-bladed switches in Frankenstein, thrown by one ominous handle).”
corpus · nicolas-collins-handmade-electronic-music-the-art-of-hardwar · chunk 25

Taught in modules