An electric switch is a device – usually electromechanical – used to open and close an electric circuit. This disables and enables the flow of electric current, respectively.
Switches are synonymous with the interruption, or some form of manipulation, of the flow of electric current or, more elementarily, the flow of electrons.
The appreciation of the underlying principle behind a switch comes along with electricity and the use of conducting material for electric current to flow. A discontinuity in the conductor implies the current does not flow. Switches are as old as the discovery of the first practical application of electricity and the construction of the first electrical circuit.
As inferred, a switch effectively puts an air gap between some parts of the circuit. The air gap has different electrical properties to the conducting material building the circuit and will stop the current flow if it is big enough. That is the fundamental purpose of a switch i.e. to alter the electrical properties of some part of a circuit to alter the flow of electrons in that circuit. By contrast, the operation of some switches never involves physical movement.
Operation of Electric Switches
Switches provide a means to control the electrical current supply to electric loads. A crucial aspect of a swtitch is the ability to conduct and break and electric current as desired by the operator.
For many electric switches, breaking the circuit involves putting an air gap between two contacts. The contacts must be opened fast enough to ensure the desired operation.
For most electronic switches, the state of the connection is changed by changing the effective resistance of that connection. The resistance can be made very high to effectively make it an open circuit or made low enough to close the circuit. It is common to have no physically moving components on the switch itself.
Another important aspect is the ability to respond to the actuator. The actuator may be automatic or manual and is intended to make or break the circuit. The purpose of the actuator is to initiate some change in the state of the connection. Actuation may take the form of physical movement e.g., a lever or a slide. It can also take the form of some other event, e.g., overvoltage or light intensity variation.
In the case that equipment to be connected through the switch may not be protected, a fuse is often incorporated as part of the switch.
