switch

In electronics, a switch is an electrical component which can break an electrical circuit, interrupting the current or diverting it from one conductor to another. The most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts. Each set of contacts can be in one of two states: either 'closed' meaning the contacts are touching and electricity can flow between them, or 'open', meaning the contacts are separated and nonconducting.

In the simplest case, a switch has two pieces of metal called contacts that touch to make a circuit, and separate to break the circuit. The contact material is chosen for its resistance to corrosion, because most metals form insulating oxides that would prevent the switch from working. Contact materials are also chosen on the basis of electrical conductivity, hardness (resistance to abrasive wear), mechanical strength, low cost and low toxicity.

Sometimes the contacts are plated with noble metals. They may be designed to wipe against each other to clean off any contamination. Nonmetallic conductors, such as conductive plastic, are sometimes used.

The moving part that applies the operating force to the contacts is called the actuator, and may be a toggle or dolly, a rocker, a push-button or any type of mechanical linkage.

Contact arrangements

A pair of contacts is said to be 'closed' when there is no space between them, allowing electricity to flow from one to the other. When the contacts are separated by an insulating air gap, an air space, they are said to be 'open', and no electricity can flow at typical voltages.

switch es can be and are classified according to the arrangement of their contacts in electronics fields— but electricians in the electrical wiring service business and their electrical supplier industries use different nomenclature, such as "one-way", "two-way", "three-way" and "four-way" switch es—which have different meanings in North American and British cultural regions as is delineated in the table below.

Some contacts are normally open (Abbreviated "n.o." or "no") until closed by operation of the switch , while others are normally closed ("n.c. or "nc") and opened by the switch action, where the abbreviations given are commonly used on electronics diagrams for clarity of operation in assembly, analysis or troubleshooting. They serve to synchronize meaning with possible mistakes in wiring assembly, where wiring part of switch one way and part another (usually opposite) way will pretty much guarantee things won't work as designed.

A switch with both types of contact, that can switch on a circuit in one position & can switch another circuit on in other position, is called a changeover switch or "make-before-break" switch contact, whereas most switch es have a spring loaded action which momentarily disconnect the load and so are "break-before-make" types by contrast— which type is used could be important, if for example, the switch selects two different power sources instead of switch ing circuit loads, or the circuit load will not and cannot tolerate any interruption in applied power.

The terms pole and throw are also used to describe switch contact variations. A pole is a set of contacts, the switch 's electrical terminals that are connected to and belong to a single circuit, usually a load. A throw is one of two or more positions (the nomenclature is also applied to rotary switch es, which can have many 'throw' positions) that the switch can adopt, which normally, but not always correspond to the number positions the switch handle or rotor can take when connecting between the common lead of the switch and a pole or poles. A throw position which connects no terminals (poles) has a mis-match between positions and positions which connect terminals, but are quite useful to turn things "Off" or for example, alternatively select between two scaled modes of operation. (e.g. Bright illumination, moderate illumination, no illumination.)

These terms give rise to abbreviations for the types of switch which are used in the electronics industry such as "single-pole, single-throw" (SPST) (the simplest type, "on or off") or "single-pole, double-throw" (SPDT), connecting either of two terminals to the common terminal. In electrical power wiring (i.e. House and building wiring by electricians) names generally involving the suffixed word "-way" are used; however, these terms differ between British and American English and the terms two way and three way are used in both with different meanings.