- A circuit breaker is a mechanical device that controls the flow of electrical current through a wire. True to its name, it "breaks" the connection if the current running through the wire is more than the wire can handle. A basic breaker design has a switch handle on the front, which is connected to either an electromagnet or a bimetallic strip. The breaker works automatically, but it is also possible to manually flip the switch and break the current. A breaker usually has four settings: on, off, tripped and reset. The breaker will display the "tripped" setting when it has automatically turned itself off.
- When electricity enters a house, it runs through the breaker box, and each wire circuit is connected to an individual breaker. As electricity travels through a wire, it produces heat and a magnetic charge. When the current is at or below the capacity of the wire, the breaker keeps the circuit open. But if the demands on the wire are greater than capacity, as with a power surge, the wire will overheat. Once the wire overheats, at best it will melt or burn out or damage whatever appliance is connected to it. At worst, the overheated wire will start a fire. Breakers are an essential part of the home's electrical system, because they prevent fires and electrical malfunctions by stopping the electrical current before the wire overheats.
- A bimetallic breaker has a strip made up of two different metals bonded together. The different metals have different conductivity and expand at different rates. As current runs through the breaker, the two metals heat up (and expand) at different rates, causing the strip to bend. The strip is connected to a series of levers, which are connected to the breaker switch. When the strip bends too far, it presses on the levers, which flip the breaker switch. Once the switch is flipped, it blocks the flow of current through the breaker, breaking the circuit and protecting the wire from overheating.
- A magnetic breaker has a metal coil placed close to a metallic plate. The metallic plate is connected to a series of levers connected to the breaker switch. As current flows through the breaker, it magnetizes the coil. Under normal conditions, the magnetic field around the coil is not enough to move the metal plate. If the current exceeds the threshold of the wire, the magnetic field increases until the coil moves the plate, flipping the switch on the breaker and breaking the circuit.
