This relay can be used to switch High power (whether AC or DC) to a load by driving the relay coil with a far much lower voltage and current. When Current flows through the relay coil, It makes or breaks its contacts through electromagnetic induction. A relay contacts comprises of the Normally-Open (NO) and Normally Closed (NC) contacts. These refer to the state of the relay contacts when the relay coil is not energized. When driving a relay coil from a digital output or transistor, always connect a diode in reverse bias across the coil of the relay in other to avoid the resulting back-emf that appears across the coil of the relay when its turned off from damaging the digital device or transistor.