What is a defining characteristic of non-restorable fusible elements in heat detectors?

• A. They reset automatically after cooling
• B. They permanently activate when the temperature is reached
• C. They require battery replacement
• D. They respond to smoke

Answer: (B)

Non-restorable fusible elements in heat detectors act as one-time triggers. When the surrounding temperature reaches the preset rating, the fusible element melts or a welded link opens, permanently activating the device so it cannot be reset. After tripping, the detector must be replaced. This behavior ensures a definitive indication that a high-temperature event occurred and prevents reuse after a fire risk. It’s not about battery replacement, which is a power issue, and it’s not about smoke detection, since heat detectors rely on heat, not smoke.