Breakers

The circuit breaker is an absolutely essential device in the modern world, and one of the most important safety mechanisms in your home.Whenever electrical wiring in a building has too much current flowing through it, these simple machines cut the power until somebody can fix the problem. Without circuit breakers (or fuses), household electricity would be impractical because of the potential for fires and other dangers resulting from simple wiring problems and equipment failures.

In building wiring, the hot wire and the neutral wire never touch directly. The charge running through the circuit always passes through an appliance, which acts as a resistor. In this way, the electrical resistance in appliances limits how much charge can flow through a circuit (with a constant voltage and a constant resistance, the current must also be constant). Appliances are designed to keep current at a relatively low level for safety purposes. Too much charge flowing through a circuit at a particular time would heat the appliance's wires and the building's wiring to unsafe levels, possibly causing a fire.  For example, a fan motor might overheat and melt, fusing the hot and neutral wires together. Or someone might drive a nail into the wall,  accidentally puncturing one of the power lines. When the hot wire is connected directly to ground, there is minimal resistance in the circuit, so the voltage pushes a huge amount of charge through the wire. If this continues, the wires can overheat and start a fire.