Mercury relay
![Normally closed mercury relay, with coil around top of tube and adjustable angle.](/Images/godic/202501/26/Mercury_relay5016.jpg")
![Normally open mercury relay, with coil around bottom of tube](/Images/godic/202501/26/Mercury_contactor5016.JPG")
A mercury relay (mercury displacement relay, mercury contactor) is a relay that uses mercury as the switching element.
They are used as high-current switches or contactors, where contact erosion from constant cycling would be a problem for conventional relay contacts.