Definition
A circuit protection device that opens an electrical circuit when excessive current causes a strip made of two bonded metals with different rates of thermal expansion to heat up and bend, tripping the breaker mechanism. Once the strip cools, the breaker can be reset manually.
Plain English
A switch that automatically pops open when too much electricity flows through it, protecting the wiring from overheating. It works because heat makes a small metal strip inside it bend and release the switch.
Context Anchor
Seen on aircraft circuit breaker panels, in electrical system descriptions, and in abnormal procedures for electrical equipment that stops working.
Derivation
Bimetallic comes from the Latin 'bi-' (two) and 'metallum' (metal). Two metals are bonded together; because each expands at a different rate when heated, the strip bends predictably with temperature. That bending is what trips the breaker.
Why Pilots Care
It prevents overheating and fire in aircraft wiring by automatically cutting power during overloads or short circuits.
Analogy
It is like a heat-sensitive safety latch. Too much electrical flow creates heat, the latch bends, and the switch opens to stop the flow.
Intuition Check
Do not assume it trips only because a switch was moved by hand. A bimetallic circuit breaker trips because electrical heat bends two joined metals inside it.
Example Sentence 1
When the landing light circuit drew too much current, the bimetallic circuit breaker tripped and cut power to the light.
Example Sentence 2
During the preflight inspection the mechanic confirmed all bimetallic circuit breakers were closed and properly labeled.