DoubleThrow

Doublethrow is a term used in electrical switching to describe a contact arrangement in which a single common terminal can connect to one of two separate output terminals, or throws. It is most commonly encountered in single-pole double-throw SPDT devices, such as toggle switches, pushbutton switches, relays, and contactors. The defining feature is that the common contact can be connected to either of two circuits, allowing a choice between two signal paths or power sources.

In practice, doublethrow devices provide three connection points: one common and two throws. The two throws form the two possible connection states, and a mechanical actuator moves the connection from one throw to the other. Some variants support an off position or center detent, while others are designed for continuous on-one-side operation. Depending on design, the contact sequence can be make-before-break (shorting) or break-before-make, which affects how quickly the new path is established relative to breaking the old one.

Doublethrow configurations are used to route signals or power, select between two sources, or implement simple control logic. They are common in control panels, signal routing in audio or instrumentation systems, and as part of relays and interlock circuits. Electrical ratings, contact material, and mechanical actuation characteristics influence suitability for a given application.

See also: single-pole single-throw, single-pole double-throw, relays and contactors, switchgear.