A 80a latching relay is a switch which can be used to control high current circuits using a low power signal. These relays have the added benefit of positional'memory' which means they will remain in their last actuated position until explicitly told to change by a new current pulse. This makes them particularly useful when controlling high current equipment, especially if it must be powered on/off repeatedly. They are also known as keep impulse, bi-stable, or stay relays and operate on a different principle to other relay switch types.

When the relay is energised via a short pulse of current from a +12V source (usually the output signal from an alarm system) its coil(s) generate a magnetic field which moves the armature - often shown as a strip suspended between two terminals - to either make or break a contact. This allows the relay to switch a circuit on or off and can be set up as a make/break or a common/non-common switch.

To prevent damage to sensitive equipment upstream of the relay coil, a diode is typically installed across the coil. This will absorb the sudden high voltage spikes generated by the energised relay and dissipate them internally, protecting the equipment from damage. It is important that the diode is connected with its stripe facing towards terminal 86 and that +12V is supplied to this terminal (with 85 connected to ground).

Once the relay's coil has been de-energised, its magnetic field collapses rapidly and creates a voltage across the contacts which closes them. This voltage is also created by the current that was feeding the relay's armature when it was energised and will be higher than the supply voltage. This is why it's important to use a relay with an integrated diode, which will protect the relay and any other devices downstream of it from damaging voltage spikes.

In some applications the diode may not be required, but in others it is essential to avoid damage to sensitive equipment upstream of the relay. It is also worth noting that relays can be manufactured with a Type A or a Type B layout, this will affect how the terminals are labelled on the relay body and so should be taken into consideration when designing a circuit.

The 'common' terminals on the relay are shown as either COM or NC depending on the manufacturer, this is because some manufacturers have swapped the pins around in order to make them easier to work with. It is important to understand this when buying relays so that you can ensure they are fitted correctly and the correct connections are made. If you are unsure about the terminal layout on a relay ask the supplier or consult an electrician. They will be able to confirm the correct wiring and also provide you with some helpful information on any additional safety precautions to take. This will include the need for a fuse in the circuit and the fact that the relay should not be used at voltages greater than its rated coil voltage.