SPDT Relay Controller
This device has SPDT relays installed. SPDT Single Pole Double Throw Relays have three connections - Common, Normally Open, and Normally Closed. When the relay is off, the common is connected to the normally closed connection of the relay. When the relay coil is energized, the Common swings over to the Normally Open Connection of the Relay. You can wire the device you are switching to either the Normally Open or the Normally Closed position. For more information on selecting the correct relay amperage for your application see Choosing a Proper Amperage.