Mercury relay is a type of electromagnetic relay with liquid contact formed by mercury - the only liquid metal element.
It was used quite often in the past, but then due to the toxicity of mercury
it started to be replaced by other types of switches, such as relays and contactors with conventional contacts (which, however, have
less durability and reliability) or semiconductor devices (MOSFETs, IGBTs, thyristors, triacs and SSR - Solid State Relay).
The principle of operation of the relay on the pictures: iron cylinder floats on mercury. If the current flows in the coil, cylinder is forced into the coil
and thus immersed in the mercury. The mercury level rises to the upper contact.
Warning - poison! Environmental hazard!
This type of relay should be handled very carefully to avoid breaking the glass tube of the switch and spilling the mercury!
If the mercury is spilled, the area must be decontaminated! When the mercury is not sealed in gas-tight container,
it produces poisonous vapor.
Mercury displacement relay Křižík n. p. Děčín, MRA15 type with one normally open contact 15A / 220V~. The coil is rated 120V~.
The relay in cabinet.
The relay from bottom.
Opened relay. Operating position must be left side up.
Switch that I removed from the relay for the moment to take a picture.
Mercury switch again.
Mercury Switch (it is upside down - short electrode must be at the bottom and a long one at the top in operation).