text: what is difference between circuit breaker and contactor?   most circuit breakers are thermal devices that when excess current run through them they heat up and trip (open up). they can also be used as a switch to open a circuit.  a contactor is a electric relay that is essentially a solenoid and a pair of electrical contacts. the solenoid is activated and it closes the contacts. they are typically used to permit a low voltage circuit or small switch to activate the solenoid so the much larger "switch" in the form of the contacts can close a higher voltage or higher amperage circuit. they can also be used for remote control of a electrical circuit.  a good example if the starter solenoid on your car. it is really a contactor activated by the turning of the key to start the car. the amperage to run the starter motor is relatively large and requires relatively large wiring and a "large" switch.