An electrical relay is a switch that is under the control of another circuit. Relays are usually made with electromagnets, whereas some applications use solid state relays. The main difference between electromagnetic relays and solid state relays is that electromagnetic relays have moving parts, contrary to solid state relays. It is also to be noted that electromagnet relays conserve more energy than solid state relays. An electrical relay can control electrical output that is higher than the electrical input it receives.