USCG Exam PracticeElectrical troubleshooting and maintenance
The thermal tripping element in a molded-case circuit breaker is designed to respond in which manner to a sustained overload condition?
- A. It trips instantaneously regardless of the magnitude of the overload current
- ✓ It trips with an inverse time delay, tolerating brief inrush but tripping faster as the overload increasesCorrect
- C. It trips only after the magnetic element has first operated and reset
- D. It trips at a fixed time delay of 30 seconds regardless of overload magnitude
Why B is correct
NEETS Mod. 3 §2-2 describes the thermal element (bimetallic strip) as having an inverse time delay characteristic — it tolerates brief inrush current but trips faster the greater the overload. Instantaneous tripping on short-circuit current is the function of the magnetic element, not the thermal element.
Cited:NEETS Mod. 3 §2-2