What is a relay and why is it used in bus electrical circuits?

• A. A relay is an electrically operated switch used to control high-current devices with a low-current signal, enabling protection and remote operation.
• B. A fuse that protects against overcurrent.
• C. A sensor that monitors temperature.
• D. A passive resistor for current limiting.

Answer: (C)

Relays are electrically operated switches that let a small control signal switch a much larger load current. In bus electrical circuits, this means a low-power coil can be energized to open or close contacts that power motors, lights, or other high-current devices, without sending heavy current through the control wiring. This provides isolation between the control circuitry and the power circuit, protects the control electronics from faults, and enables remote or centralized operation and interlocking of multiple devices via a single control signal. A fuse, by contrast, is a protective device that sacrifices itself to interrupt overcurrent and does not act as a controllable switch. A temperature sensor merely monitors heat, not switch power. A passive resistor changes current or voltage but does not switch loads.