Reed switches are magnetically actuated switches. They are typically manufactured with two ferromagnetic reeds (contact blades), which are sealed in a glass capsule. In the presence of a magnet, the blades (contacts) close.  Reed switch types are dry reed switch or mercury wetted reed switch.  A dry reed switch contains ferromagnetic contact blades sealed in a glass container with an inert gas.  In a mercury wetted reed switch, mercury is contact material for electrical circuit, mercury to mercury. The contacting faces are renewed by capillary action drawing a film of mercury over the surfaces of the constant switching members as the movable contact member is moved from one position to another.  The center position on reed switches can be center gap or off center gap.  The gap is the contact meeting of the switch.

 

How a Reed Switch Works

 

Pole and Throw Configurations

Pole and throw configurations for reed switches can be single pole single throw (SPST), single pole double throw (SPDT), double pole single throw (DPST), or double pole double throw (DPDT).  SPST is a switch that makes or breaks the connection of a single conductor in a single branch circuit. This switch typically has two terminals. It is commonly referred to as a "Single-Pole" Switch.  SPDT is a switch that makes or breaks the connection of a single conductor with either of two other single conductors. This switch typically has 3 terminals, and is commonly used in pairs and called a "Three-Way" switch.  DPST is a switch that makes or breaks the connection of two circuit conductors in a single branch circuit. This switch typically has four terminals.  DPDT is a switch that makes or breaks the connection of two conductors to two separate circuits. This switch typically has six terminals and is available in both momentary and maintained contact versions.  A normally open (NO) switch has contacts that are open or disconnected in their unactuated (normal) position.  A normally closed (NC) switch has contacts that are closed or connected in their unactuated (normal) position.

Specifications

Important electrical switch specifications to consider when searching for reed switches include current rating, AC voltage rating, DC voltage rating, and power rating.  Important dimensions to consider include glass encapsulated length, total length including leads, and diameter.  Common features for reed switches include hermetically sealed, CE certified, CSA certified, UL listed, and weather resistant or waterproof. 


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