When relay activates, the NC terminal disconnects with the COM terminal and stays open till the relay is deactivated. How come relays click? Any time a relay clicks it is an indication of your contacts opening/closing if the coil is powered. Some relays come up with a louder clicking noise https://smtp12332.wikilinksnews.com/5255045/the_fact_about_relay_that_no_one_is_suggesting