The 24 volt double pole relay is a simple to fit module wherever a dry contact, voltage free switching is required or where there is a need for higher than usual currents and voltages to be switched. The polarised function enables it to be used in Fire Alarm and similar systems where the polarity of the output to the bells, sounders etc. is reversed when in alarm.
Polarity must be correct for the relay to activate. The 24 Volt relay is mounted on a printed circuit board that has screwed terminals, complete with LED indication that the relay is activated.