What Is the Function of a Circuit Breaker?

A properly designed electrical system is very safe. However, when problems occur, electricity can generate dangerous heat and can be fatal to people and animals. Circuit breakers can cut the electricity supply when a fault is detected.

Circuit breakers are mechanical switches that open when an electrical fault is detected. Circuit breakers have replaced fuses in modern electrical systems. In a fuse, excess electricity or heat melts a metal strip, thus interrupting the flow of electricity. The problem with fuses is that they only can be used once. A circuit breaker can be switched back on as part of trouble-shooting or when the fault has been fixed.

In a circuit breaker, electricity generates a current in an electromagnet. The electromagnet is strong enough to pull down on a lever that is connected either to a spring or to another electromagnet. When the electrical flow exceeds design tolerances, the bar snaps down, thus cutting off electrical flow.

Simple domestic circuit breakers are designed to prevent damage to home wiring. Damage is usually caused by plugging too many high power devices, like electric heaters, appliances and high power lights, in to a circuit. When the circuit breaker senses the overload, it trips interrupting the flow of electricity and preventing damage to home wiring.

Ground fault, or GFI, circuit breakers are designed more to prevent shocks to people. A GFI circuit breaker is a solid state device that senses when there is a ground fault. Ground faults often occur when an electrical device is dropped in water or the user is standing in water. GFI breakers are usually found in kitchens, bathrooms and other rooms where water is often found.

Commercial circuit breakers are designed to protect extremely high voltage circuits. The basic working principles are the same, but some large commercial breakers include digital or solid state circuitry to sense and calculate pre-defined safety criterion in commercial applications.