A Switch is a device for making and breaking the connection in an electric circuit.
Besides Connectors, Switches are probably the 2nd Most Common Electronic Part. There are so many different
Shapes and Sizes of switches. Farnsworth Electronics carries Hundreds of Switches IN Stock.
Not sure what type of Switch you need? Click here to check out the Switch Reference Guide
Click here to view The Switch Glossary of TermsCheck out some of the categories below to get started.
Switch Reference Guide - SPST, SPDT, DPST, DPDT
Courtesy of Littelfuse
SP and DP refer to Single Pole and Double Pole.
ST and DT refer to Single Throw and Double Throw.
SP: Single Pole, one circuit controlled by the switch.DP: Double Pole two independent circuits controlled by the switch which
are mechanically linked.Note: “Pole” should not be confused with “Terminal”. The DPST switch,
for example has four terminals however is a Double Pole (DP) and not
a four pole (4P) switch.ST: Single Throw, closes a circuit at only one position. The center position
is off.DT: Double Throw, closes a circuit in the up or down position (On-On).
A Double Throw switch can also have a center position such as On-Off-On.
Glossary Of Switch Terms:
Actuation Force: See Operating Force.Actuator: An actuator is the mechanical component used to manually turn a switch or circuit breaker on and off.Alternate Action (Double Action): A “Push−On/Push−Off” switch action, typically referring to maintained circuit pushbutton switches.Arcing: Sparking that occurs each time a switch is turned on or off, except in very low voltage and low current applications. This sparking can burn up the switch contacts and reduce the life of a switch. In general, the arc produced by a DC voltage will be greater and last longer than an AC voltage because DC current has a constant value in relation to ground and zero. AC current has a value that is always rising or falling in relation to zero. Whenever it reaches zero (120 times a second) it cannot produce an arc.Break−Before−Make: Switches that will only complete one circuit at a time, leaving an interval of time between the time one circuit opens and the next circuit closes.Center−Off: A switch with three actuator positions. Contact is made (with one or several circuits) in the two extreme positions; in the center position of the actuator, all circuits are off.Contact Resistance: The resitance of a pair of contacts, measured at the terminals, which effectively appears in series with the load (milliohm range).
Current Rating: The maximum current in amperes, at rated current and frequency, that a device will carry continuously under defined conditions withoutexceeding specified performance limits.Dielectric Strength: The highest voltage an insulator can withstand without allowing current to flow. Also referred to as breakdown voltage. For switches, alsorepresents the strength between live parts and operator at accessible surfaces.Double Break/Double Make: Contacts that open at two separate places on a circuit.Double Pole (DP) Switches: A switch device that opens, closes, or changes connection of two conductors in an electrical circuit.Double Throw (DT) Switches: A switch that opens, closes, or completes a circuit at both extreme positions of its actuator.Insulation Resistance: The resistance between two normally insulated parts measured at a specified high DC potential (megohm range). Also referred to asLeakage Resistance.Life Expectancy (Useful Life): Depends upon the end life criteria for a specific application. In order to determine your failure criteria, the following parameters should be known; dielectric strength, duty cycle, mechanical breakdown, contact resistance, insulation resistance, operating force. Life expectancy is normallyexperienced in minimum switch cycles before failure.Make−Before−Break: Switches that complete a new circuit before breaking an old one.Momentary Switch: A switch that automatically returns to its original, or at rest position.
Normally Closed: Often abbreviated N.C., indicates that the circuit is closed when the switch is not operated. Activation of the switch causes the circuit to open.Normally Open: Often abbreviated N.O., indicates that the circuit is open when the switch is not operated. Activation of the switch causes the circuit to close.Operating Force: Also known as Actuation Force, the force required to transfer a switch from one position to another.Pole: The number of completely separate circuits that can be active through a switch or simultaneously protected by a circuit breaker at any on time.Push−On/Push−Off: An alternate action switch, often used on lamps, vacuum cleaners, etc. When pushed, the circuit closes. When pushed again, it opens. Oftencalled “Push−Push”.Quick Break/Quick Make: Switches designed to make or break circuits in less than 5 milliseconds to make or break. Recommended for use on DC circuits.Single Break/Single Make: Contact that open and close a circuit at only one place.Single Pole (SP) Switches: A switch device that opens, closes, or changes the connection of a single conductor in an electrical circuit.
Single Throw (ST) Switches: A switch that opens, closes, or completes a circuit at only one of the extreme positions of its actuator.Slow Break/Slow Make: Switches designed to make or break circuits within 8−12 milliseconds. Typically used for AC applications.
Snap−Action: Non−teasable switch action having unstable equilibrium so that it must be either “ON” or “OFF”. Can also be referred to as “Push−Push”.Wiping Action Contacts: Self−cleaning contacts that wipe or slide against each other when opening or closing a circuit.
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