In heating detectors, a fusible element that cannot be reset means what happens after activation?

• A. Detector can be reset and reused
• B. Detector must be replaced
• C. Detector remains active indefinitely
• D. Detector automatically reverts to standby

Answer: (B)

A fusible element that cannot be reset creates a one-shot detector. When heat activates this element, it fuses open and permanently breaks the electrical path. Because the sensing element is damaged irreversibly, the unit can’t be reset to normal operation and must be replaced to restore protection. It doesn’t stay active indefinitely, and it doesn’t automatically return to standby—there’s no mechanism to reset a non-resettable element in the field.