Relays are switches that are used to control one circuit with another.. Relays control one electrical circuit by opening and closing contacts in another circuit. When a relay contact is Normally Closed , there is a closed contact when the relay is not energized. Applying electrical current to the contacts will change their state. Relays are generally used to switch smaller currents in a control circuit and do not usually control power consuming devices except for small motors and Solenoids that draw low amps. Nonetheless, relays can “control” larger voltages and amperes by having an amplifying effect because a small voltage applied to a relays coil can result in a large voltage being switched by the contacts.