Which device is a limit switch that automatically controls circuits, preventing dangerous operation?

• A. Microswitch
• B. Rotary selector
• C. Fuses
• D. Relays

Answer: (A)

A limit switch is a safety device that detects the position or end of travel of a mechanism and automatically opens or closes a circuit to prevent hazardous motion. A microswitch is a small, snap‑action limit switch with a lever or button actuator designed to respond quickly and reliably. When the mechanism reaches its limit, the microswitch rapidly changes its contacts, cutting power or changing the circuit to stop movement and keep things from operating in a dangerous way.

Rotary selectors are manual controls used to choose settings, not to automatically stop motion. Fuses protect circuits by breaking the circuit when current is too high, but they don’t actively control operation to prevent dangerous movement. Relays are switches operated by a control circuit, capable of controlling circuits, but they aren’t specifically limit switches used to detect position and automatically prevent unsafe operation.