How Circuit Breakers Work


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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 the alternative, fuses), household electricity would be impractical because of the potential for fires and other mayhem resulting from simple wiring problems and equipment failures.

In this article, we'll find out how circuit breakers and fuses monitor electrical current and how they cut off the power when current levels get too high. As we'll see, the circuit breaker is an incredibly simple solution to a potentially deadly problem.

To understand circuit breakers, it helps to know how household electricity works.

Electricity is defined by three major attributes:

  • Voltage
  • Current
  • Resistance

Voltage is the "pressure" that makes an electric charge move. Current is the charge's "flow" -- the rate at which the charge moves through the conductor, measured at any particular point. The conductor offers a certain amount of resistance to this flow, which varies depending on the conductor's composition and size.

­Voltage, current and resistance are all interrelated -- you can't change one without changing another. Current is equal to voltage divided by resistance (commonly written as I = v / r). This makes intuitive sense: If you increase the pressure working on electric charge or decrease the resistance, more charge will flow. If you decrease pressure or increase resistance, less charge will flow. To learn more, check out How Electricity Works.

So how does all of this come together in your home? Let's find out.