What is a relay in an irrigation controller circuit?

• A. A potentiometer
• B. An electrically operated switch
• C. A fuse
• D. A transformer

Answer: (B)

A relay is an electrically operated switch that uses a small control current to switch a larger current in a separate circuit. In an irrigation controller, the controller sends a low-voltage, low-current signal to the relay coil. Energizing the coil creates a magnetic field that pulls the switch contacts to close (or open, depending on the design), thereby powering the valve solenoids without the controller having to supply the valve current directly. This provides electrical isolation between the controller and the valve circuits and allows one controller to drive multiple valves safely.

Compared to the other components: a potentiometer adjusts signal levels rather than switching power; a fuse protects against overcurrent rather than enabling or disabling a circuit; a transformer changes voltage but does not provide the on/off switching action used to control valves.