Definition
An electrical switch that opens or closes its contacts in response to a change in temperature. The switching action is driven by a temperature-sensitive element, typically a bimetallic strip or a fluid-filled bulb, which physically moves the contacts when a preset temperature is reached.
Plain English
A switch that turns a circuit on or off automatically when something gets too hot or too cold. Heat does the work of flipping the switch instead of a person pressing a button.
Context Anchor
Seen in aircraft electrical, engine, heater, and warning systems where temperature must start or stop an action automatically.
Derivation
From Greek therme, meaning heat, and Latin actuare, meaning to set in motion. Together: a switch set in motion by heat. The word origin matches the function exactly.
Why Pilots Care
These switches automatically alert the crew to dangerous overheating or fire conditions so immediate corrective action can be taken.
Analogy
It works like a home device that turns heat on or off when the room reaches a chosen temperature.
Intuition Check
Do not think of this as a normal cockpit switch that the pilot flips. The temperature itself is what makes the switch operate.
Example Sentence 1
The fire warning light in the engine bay is triggered by a thermally actuated switch that closes when temperatures exceed a safe limit.
Example Sentence 2
During the preflight inspection the mechanic tested the thermally actuated switch to confirm it would activate at the correct temperature limit.