text: 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.\n\nA 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.\n\nA 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.