When the coil is energised, by passing current through it, the core becomes temporarily magnetised.

The magnetised core attracts the iron armature.

The armature is pivoted which causes it to operate one or more sets of contacts.

When the coil is de-energised the armature and contacts are released.

The coil can be energised from a low power source such as a transistor while the contacts can switch high powers such as the mains supply.

The relay can also be situated remotely from the control source.

Relays can generate a very high voltage across the coil when switched off.

This can damage other components in the circuit.

To prevent this a diode is connected across the coil.

The cathode of the diode is connected to the most positive end of the coil.

Various coil operating voltages (ac and dc) are available.

The actual contact points on the springsets are available for high current and low current operation.

The REED RELAY has a much faster operation than the relays described above.

When the "start" button is pushed, the 12 volt circuit is completed and the relay is energised. The three sets of contacts close and 240 volts is applied to the motor.

Since there is now a closed relay contact across the "start " switch, when the button is released the relay continues to be energised and the motor continues to run.  The relay has "latched on".

When the "stop" button is pushed the 12 volt circuit is broken. The relay is de-energised and the motor stops.