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Switch Basics[edit]

It has been suggested that [[::Switch Terminology|Switch Terminology]] be merged into this page or section. (Discuss)

A switch is often to turn something on or off. In the simplest case it is just a wire that is connected or not. Unplugging an appliance is one way to switch it off. A switch is usually a mechanical device where some sort of handle connects or disconnects conductors inside the switch. Another way of thinking of a switch is that it is like a resistor that sometimes has infinite resistance and sometimes has 0 resistance. A computer keyboard is made of a large number of switches. Some switches stay in the on or off position, others only stay on or off while you switch them, these are called momentary switches. A light switch is normally not momentary, a doorbell switch normally is momentary.


  • On Off control
  • Range change, as in a meter
  • Data input



It has been suggested that [[::relays|relays]] be merged into this page or section. (Discuss)

A Relay is a switch that is turned on and off by an electro-magnet ( actually there are new forms that do not use an electro-magnet ). Like other switching devices it allows a small amount of power to control a large amount of power. A nice feature of relays is that there is no electrical connection between the control circuit and the circuit connected to the switch. ( this is called electrical isolation ). They are often used to let low power digital circuits control normal 110v power in a home.


  • Turn on several circuits with one control circuit.
  • Control motors.
  • Isolate a low voltage circuit from power line.
  • Reverse current ( double pole double throw relay )