Which protective device is a one-time device that opens the circuit when overloaded and cannot be reset?

Which protective device is a one-time device that opens the circuit when overloaded and cannot be reset?

• A. Fuse
• B. Circuit breaker
• C. Relay
• D. Switch

Answer: (A)

Overcurrent protection that is used up and cannot be reset is provided by a fuse. A fuse contains a metal conductor designed to melt or vaporize when the current exceeds its rating, causing the circuit to open and stop the current flow. This intentional failure protects wiring and equipment from damage due to overload or a short circuit. Because the fusible element is destroyed, it cannot be reset; you replace the fuse after it blows. In contrast, a circuit breaker also interrupts current when there’s an overload, but it trips and can be reset after the fault is cleared. A relay is an electrically actuated switch used in control circuits, not primarily a protective device for overloads. A switch is a manual control and does not automatically interrupt power due to overload.

Overcurrent protection that is used up and cannot be reset is provided by a fuse. A fuse contains a metal conductor designed to melt or vaporize when the current exceeds its rating, causing the circuit to open and stop the current flow. This intentional failure protects wiring and equipment from damage due to overload or a short circuit. Because the fusible element is destroyed, it cannot be reset; you replace the fuse after it blows.

In contrast, a circuit breaker also interrupts current when there’s an overload, but it trips and can be reset after the fault is cleared. A relay is an electrically actuated switch used in control circuits, not primarily a protective device for overloads. A switch is a manual control and does not automatically interrupt power due to overload.