Thermal protectors or thermostats use a snapaction, bi-metallic, disc type switch to open or to close the circuit when it reaches a certain temperature. A thermal relay switch is usually used to protect motors from thermal damage by automatically disconnecting them when the motor. Thermal switches and thermal protectors are thermally-actuated electro-mechanical on/off switches. The switch is activated by a temperature differential. Common terms include thermal switch, heat-activated switch, thermostat, temperature controller, thermal cut-out, thermal relay, or thermal protector. It's a small but absolutely essential device that keeps an eye out for the electrical equivalent of a fever—a sustained overcurrent—and steps in to shut things down before catastrophic damage occurs. It has a set of input terminals for one or more control signals, and a set of operating contact terminals.
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