Definition
A circuit-protection device that opens an electrical circuit when excessive current flow heats a bimetallic element enough to cause it to bend and trip the breaker open. Once the element cools, the breaker can be manually reset to restore the circuit.
Plain English
A safety switch that uses heat to detect electrical overload. When too much current flows, the heat bends a small metal strip inside, which snaps the switch open and stops the flow. After it cools, you can push it back in to reuse it.
Context Anchor
Seen on aircraft electrical panels, circuit breaker panels, and equipment troubleshooting checklists.
Derivation
Thermal comes from the Greek therme, meaning heat. The name describes how the breaker works -- it senses overload by heat rather than by a magnetic field or fuse element melting.
Why Pilots Care
Prevents wiring damage and fire risk by automatically disconnecting overloaded circuits.
Analogy
It works much like a home breaker that trips when too many appliances are drawing power on one circuit. The breaker opens the path before the wiring gets dangerously hot.
Intuition Check
Do not assume thermal means the breaker trips only because the cockpit or outside air is hot. In this term, thermal mainly means the breaker responds to heat produced inside the breaker by excessive electrical current.
Example Sentence 1
After the landing light circuit tripped, the pilot waited a moment for the thermal circuit breaker to cool before resetting it.
Example Sentence 2
After clearing the short, the pilot reset the thermal circuit breaker to restore power to the avionics.