Which device is typically used to control high-current circuits with a low-current signal?

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

Answer: (B)

A relay is used to control high-current circuits with a low-current signal. It works like an electro-magnetic switch: a small current energizes a coil, creating a magnetic field that pulls contacts together (or apart) to open or close the high-current circuit. This setup lets a controller or sensor operate large loads—like pumps or motors—without having to pass high current through the control wiring, providing protection and isolation for the control side.

Fuses protect circuits by breaking when current is too high, but they don’t actively switch loads in response to a control signal. A diode conducts in one direction and doesn’t switch a high-current load with a separate low-current control signal. A simple mechanical switch can control current directly but requires heavy-duty wiring and doesn’t isolate or amplify the control signal.