Editing Mercury switch (section)

{{Short description|Type of electrical switch}}
[[File:Mercury Switch without housing.jpg|thumb|A ''Single-Pole, Single-Throw'' (''SPST'') mercury switch on millimetre graph paper, device length approximately 1.5 cm]]
[[File:Mercury switch.jpg|thumb|Another mercury switch design]]

A '''mercury switch''' is an [[electricity|electrical]] [[switch]] that opens and closes a [[electrical circuit|circuit]] when a small amount of the liquid metal [[mercury (element)|mercury]] connects metal electrodes to close the circuit. There are several different basic designs (tilt, displacement, radial, etc.) but they all share the common design strength of non-eroding switch contacts.

The most common is the ''mercury tilt switch''. It is in one state (open or closed) when tilted one direction with respect to horizontal, and the other state when tilted the other direction.  This is what older style thermostats used to turn a heater or air conditioner on or off.

The ''mercury displacement switch'' uses a 'plunger' that dips into a pool of mercury, raising the level in the container to contact at least one electrode. This design is used in relays in industrial applications that need to switch high current loads frequently. These relays use electromagnetic coils to pull steel sleeves inside [[hermetically sealed]] containers.