Thermal protection is activated when an overload condition occurs. In this scenario, excessive current causes a bimetallic contact to heat up and expand, ultimately leading to the interruption of the current. The thermal response is intentionally slow to accommodate short-duration overcurrent conditions, a common situation during startup in devices like electric motors.
On the other hand, magnetic protection is triggered in response to high currents associated with electric faults. In such cases, the current generates a powerful magnetic field through induction. This magnetic field is utilized to open contacts and swiftly interrupt the circuit. The immediate response is designed to minimize the detrimental effects of electric faults, ensuring rapid disconnection for safety purposes.