A magnetic circuit breaker is a safety device designed to cut an electrical current in the event of a power surge, thus protecting electrical equipment and circuitry from damage. Overloaded circuits, loose or faulty wiring and lightning can cause the circuit breaker to trip. There are other devices able to break a circuit during a surge or short circuit, each with its own limitations. Fuses have a filament that burns during a surge, meaning that they will not work after blowing once and have to be replaced immediately to restore power. Other commonly available circuit breakers are heat-sensitive and require a cooling period after a surge, but a magnetic circuit breaker can be reset immediately, restoring power without delay.
All circuit breakers require some method of detecting the strength of an electrical current so that they can respond to a surge. Some breakers rely primarily on temperature and trip when overheated, but a magnetic circuit breaker uses an electromagnet, or solenoid, to generate a magnetic field that is used to gauge the current’s strength. When the strength of the electric current increases, the solenoid’s magnetic field increases as well. This field pulls on a metallic lever in the breaker. This lever is held in place by a spring, and under normal conditions, the magnetic field is not strong enough to make the lever move.
The magnetic circuit breaker has a rating, a preset limit on the maximum strength of current that it will allow to flow. When the current exceeds the breaker’s limit, the solenoid’s magnetic field increases to the point where it is strong enough to move the lever. The breaker trips, the contact points move apart, and the circuit is broken before any damage can be done. There no longer is any current flowing through the circuit, so the solenoid loses power as well, and losing that, it also loses its magnetic field. This means that the circuit breaker can be reset immediately.
Although a magnetic circuit breaker is excellent for dealing with spikes from short circuits and large power surges, power will remain uninterrupted if a surge does not exceed a breaker’s limit. Prolonged low-level surges can cause equipment and circuitry to overheat, potentially causing damage to devices or causing fire. A thermal magnetic circuit breaker addresses this danger by using a pair of metal strips that cause the breaker to trip if overheated.