In electrical substations, an earthing switch is applied in combination with a disconnector (earthing switches may also be free-standing). Earthing switches (ground disconnectors) are used to make the corresponding parts of the electrical circuit (and the equipment connected to it) safe to access and work upon, by bringing them to ground/earth potential. The operation of an earthing switch is interlocked with the disconnector to prevent incorrect operation i.e. contact being closed whilst circuit is energised.
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Disconnector and Earthing Switch (Courtesy of Rauscher & Stoecklin)
Earthing Switch Designs
Earthing switches are often integrated into the overall assembly of the disconnector, or, are free-standing (stand-alone) devices with their own support structure. However, integration into the disconnector is the more common design.
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Free Standing Earthing Switch (Courtesy of SIEMENS)
The dielectric insulation requirements for an earthing switch are the same as those specified for its associated disconnector. Similarly, earthing switches are also required to match the short time fault/short circuit current withstand capability of their associated disconnectors. In addition, earthing switches used for transmission line switching are required to break electromagnetic inductive and electrostatic capacitive currents induced from adjacent lines/circuits.
Additional Resources
https://en.wikipedia.org/wiki/Switch
https://www.electrotechnik.net/2011/07/earthing-switches.html
http://www.tekhar.com/Programma/Siemens/Commutacia/High_voltage/pdf_pict/leaflet_e.pdf