How a Circuit Breaker and Fuse Box Work
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Breaker and Fuse Basics
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Inside a house or business, copper wires carry electric current from the circuit breaker or fuse box to the various electric terminals. A second wire carries the electricity back from the terminal to the panel, and from there into the ground. As electricity flows through the copper wire, some of it is lost and turned into heat. The more electricity that flows through a circuit, the more heat is produced. Too much electricity, and the wires could overheat and melt or even cause a fire in the wall. Circuit breakers and fuse boxes prevent overheating by opening the circuit when too much electricity flows through, stopping the current immediately and allowing the wires to cool down.
Fuse Boxes
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Fuse boxes are the simplest electrical safety devices. When electricity flows into a particular circuit in the house, it first has to flow through a fuse. Inside each fuse is an extremely thin metal filament. Because the filament is so thin, it heats up easily. If too much electricity flows through a particular fuse it melts, stopping the flow of electricity through the entire circuit. Unfortunately, fuses can not be reused--when one goes out, it needs to be replaced before the circuit will turn on again.
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Circuit Breakers
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Instead of using a thin filament, circuit breakers use a mechanical switch to turn off power. In some circuit breakers, the current runs through an electromagnet, which is attached to a switch. The more current that runs through the circuit, the stronger the magnetic pull is. When the current exceeds a certain level, the magnet pulls the switch open and shuts down the circuit. In other circuits, a bimetallic strip triggers the breaker. The bimetallic strip is made out of two different metals attached together. Metals expand slightly when they heat, but different metals expand at different rates. The difference in expansion rate causes the strip to bend as it heats up. When too much current runs through the breaker, it overheats the bimetallic strip, causing it to bend until it trips a switch, opening the circuit. Both types of breakers can be reset by hand by flipping a switch.
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