The function of relay is not limited to only the tripping of the faulty circuit. Say after the tripping occurs , there lies still some logical context like as follows- in some case if the fault is severe, then just reset-start the system would be severe, so we need a complete lock down.Again by logical when the relay contact is closed which is very light for faster response is not capable of disconnecting the loaded trip circuit.
Thus we need some extra means to do fulfill the purposes. And this is done by auxiliary contacts.Auxiliary switch is the main important thing in modern relay. It does the sealing, holding, repeat operation of relays.Its a multi-point switch like 4,6,12,24 point.
Functions of Auxiliary contacts or switch in relay:
Disconnecting the trip circuit:
After the tripping of circuit breaker, there is still current in the trip circuit. The relay contact does complete the trip circuit but it can not disconnect this. As the relay contact is so light and weak mechanically to act fast. The disconnecting of trip circuit is done by auxiliary switch or contact.
Actuating a control circuit / Mechanical interlock
When relay trips a circuit, sometime there is provision to actuate another control circuit or system such as alarm system or there might be mechanical interlocking / jamming of another system like Circuit Breaker. This purpose fulfills by Auxiliary switch or contacts.
Relays with multiple contact configuration.
Relays are available with a variety of multiple-contact configurations.