This is a 4 channel solid state relay module. It allows you control the switching of high voltages and currents using a 5V signal coming from a microcontroller. Maximum acceptable voltage and current are 240VAC and 2A respectively. Solid state relays have several advantages over mechanical relays including having no moving parts, faster switching, and longer periods without wearing out. Applications include turning on/off lamps, fans, solenoids, and other home appliances.