SSR series Solid State Relay (SSR) is a non-contact switch consisting of microelectronic circuits, discrete electronic devices, and power electronic power devices. The opto-coupling or pulse signal is used for isolation between the control terminal and the load terminal. The input of the solid state relay uses a small control signal to directly drive a large current load.Solid State Relay (SSR) is a non-contact switch consisting of microelectronic circuits, discrete electronic devices, and power electronic power devices. The opto-coupling or pulse signal is used for isolation between the control terminal and the load terminal. The input of the solid state relay uses a small control signal to directly drive a large current load.