A relay is an important electromechanical safety device in a ship’s electrical circuit and is normally used to open the faulty circuit from the main supply when any kind of electrical fault occurs.
A relay is fitted in the Main and Emergency switchboard of the ship as a protective device. The relay has to be kept operational and healthy at all times, or else at the time of the fault, if it relay does not operate properly, the whole system may suffer the loss of power or damage.
The most common application of relays is for overload and short circuit protection.
A simple electromagnetic relay is shown in the below diagram and it will get activated when the magnetic effect of the iron core is sufficiently increased by the excess or high current in the coil which will attract the iron armature held against the spring force to trip the circuit.