Plug-in modules are convenient add-on devices for relays which offer LED indication (for ease of viewing relay status from a distance), diode protection, RC circuits, bypass and timing facilities for all socket-mounted plug-in relays.
The modules simply plug into specific sockets to enhance the relays functionality.
Depending on module selected, they can provide;
Suppression of coil back emf on switch-off
LED indication to show when the coil in energized
Protection against reverse polarity applied across the coil terminals
By-pass of troublesome leakage currents in the coil circuit
LED + varistor module
LED + varistor modules are used for AC and DC coils, reverse voltage peaks of the relay coil are limited by the varistor to approximately 2.5 times the nominal voltage of the supply.