How switches work and their structure ?

Switches are used to facilitate or to interrupt a current flow in an electrical circuit. Depending on their design, these switches can either be pushbuttons or detenting switches.

• In the case of a pushbutton, the chosen switching position is only maintained for as long as the pushbutton is actuated. Pushbuttons are used in doorbells, for example.

• In the case of a detenting switch, both switching positions (ON/OFF) are mechanically latched. Each switching position is maintained until the switch is actuated again. Light switches in houses are an example of a latching switch in use.

A further classification and selection criterion for switches is their switching status in normal position (i.e. unactuated).

Normally open contacts

In the case of a normally open contact (or N/O contact), the circuit is interrupted when the pushbutton is in its normal position. Actuating the pushbutton closes the circuit and supplies the consuming device with current. When the pushbutton is released, spring force returns it to its normal position and the circuit is interrupted once more.

Normally closed contacts

In the case of a normally closed contact (or N/C contact), the circuit is closed by spring force when the pushbutton is in its normal position. Actuating the pushbutton interrupts the circuit.

Changeover switches

The changeover switch combines the functions of an N/C contact and an N/O contact in one device. They are used to close one circuit and open another one with a single switching operation. Both circuits are briefly interrupted during the changeover.