Solid State Relays (SSRs) are electronic switch devices that are optically isolated, based on semiconductors, and do not involve moving parts. They are similar to traditional electromechanical relays but are suitable for AC or DC loads up to 660 V and can be selected with different switch circuit configurations (such as SPST, SPDT, DPST and 3PST) to adapt to the load voltage and rated current. These devices can be mounted with bases, DIN rails, sockets or board mounting. Applying a small voltage to their control input terminals can open or close the device.