The Solid State Relay (SSR) are a series of single-pole, normally open, solid state switching devices with no moving parts, capable of tens of millions of cycles of operation. It is designed to control 120V, 240V or 480V (up to 660V) alternating current (VAC), and provides zero voltage switching and 2500VAC isolation between the load terminals and the control signal.
A control signal causes the solid state relay (SSR) to switch the ac load ON or OFF just as a conventional mechanical contact switch does but with none of the problems associated with moving contact relays, such as corrosion, pitting, arcing, radio frequency interference (RFI) and bounce. The result: much longer life for the solid state relay (SSR). Advantages of Solid state relay over mechanical relays from Wikipedia.
Greegoo's Solid state relay/relais/Role/switch/modules covering panel, Din rail and PCB mount type of solid state relays, control relays, power moudules and SSR assemblies. Zero cross switching type for resistive loads or random-fire for inductive loads.