A _________is always used in the control circuit.

• A. Relay
• B. Contactor
• C. Switch
• D. Fuse

Answer: (A)

In control circuits, the device used to switch the power circuit with a separate, low-power signal is the relay. A relay has a coil that is energized by the control signal; when energized, it magnetically pulls contacts to close or open the main circuit. This arrangement provides isolation between the control side (low voltage, low current) and the power side (potentially high current), so the control electronics stay safe while still controlling a larger load. It also enables remote or automated operation and allows one control signal to actuate multiple contacts if needed. A fuse protects the circuit, not controls it, and a manual switch changes the state directly rather than controlling a separate power path. A contactor is essentially a larger relay for heavier loads, but the fundamental role in the control circuit is fulfilled by the relay.