How Relays Work Relays are switches that open and shut circuits electromechanically or electronically. Relays control one electric circuit by opening and shutting contacts in another circuit. As relay diagrams show, once a relay contact is generally open (NO), there's an open contact once the relay isn't energized. When a relay contact is generally Closed (NC), there's a closed contact once the relay isn't energized. In either case, applying electrical current to the contacts can amendment their state. Relays are sometimes accustomed switch smaller currents in a very feedback loop and do not sometimes management power intense devices with the exception of small motors and Solenoids that draw low amps. Nonetheless, relays will "control" larger voltages and amperes by having an amplifying impact because a little voltage applied to a relays coil may result in a very large voltage being switched by the contacts. Electromechanical Relays vs Solid Sta...