What is a relay and how does it work?
A relay, in layman’s terms, is simply an electronically operated switch.
When the coil is connected to a supply (typically 12-24volts DC) this creates a magnetic field which ‘Pulls down’ the lever, which in turn pushes the centre contact ‘C’ from the normally closed contact ‘NC’ to the normally open contact ‘NO’.
The switch contacts are not connected to anything in the relay shown below, they are ‘Clean’.
For simplicity they are sometimes shown on a wiring diagram as this: –
Example 1 (relay not in use). Example 2 is when the relay is activated
Bentley Security Projects & Interface Solutions UK supply a wide range of relay based devices, some of which can be seen below: