Relays

From TheBestCaseScenario

A relay is basically an electrically operated switch. In its simplest form it has a coil which generates a magnetic field when a current is passed through it, and a pair of contacts, one of which is pulled towards the other by the magnetic field.

The two halves of the relay, the coil and the contacts, are electrically isolated. This makes the relay useful for controlling circuits which are otherwise completely seperate. An example would be using a computer to switch on the lights, or close the curtains.

Most relays have at least three contacts: These are common (C), Normally Closed (NC) and Normally Open (NO). 'Normaly' refers to the condition where the relay coil is not energised. In this state the common is connected to the normally closed contact. Energising the relay moves the common from the normally closed to the normally open.

Relays can have multiple poles, all of which change together when the coil is energised.