The second thing that may have occurred to Thomas Edison after getting his first light bulb turned on was how will I now turn it off? This application is now a large and central consideration of everything we do in electrical systems. The initial concept is quite easy to understand - current is flowing to an electrical load causing it to operate as designed. We now wish to turn this load off, hence stop the current flow. At lower voltages and currents, a manually operated switch is usually sufficient. Even at these lower levels though, most of us are aware of the potential for arcing when a switch is "teased" (slowly opened or closed). This arcing or ionization of the air between two separating potentials is the primary critical design criteria for a circuit breaker. A circuit breaker by simple description is any device, which inserted in an electrical circuit will successfully interrupt the current flow on demand. In this definition all manner of switches, contactors and breakers are included.
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