Electronics Questions: How Circuit Breakers Work

Electricity is so common place in sour society that its danger is often overlooked. The circuit breaker's simple design and ease of use has essentially mitigated the dangers that exist to us and our equipment.

Electricity is essential in our modern society. Our homes, cars, appliances and electronics all depend on reliable electricity. To ensure that the electricity that enters our home is reliable and not dangerous, the circuit breaker is used. Essentially the circuit breaker is a safety device. If too much current flows through the circuit breaker, the circuit breaker will "trip", not allowing the current to flow any further through the circuit, or into your home.

Circuit breakers are used to protect individual components as well. In an aircraft, circuit breakers protect each and every component in the aircraft. If a generator should produce a "spike" in voltage, the circuit breaker will trip. The component will lose power, but not be damaged. The circuit breaker could then be reset and the component usable again.

A car is primarily protected by fuses. A fuse is different than a circuit breaker. A fuse is a thin piece of wire included in a circuit. If too much current flows through the circuit the thin wire will melt, breaking the circuit. This too protects individual components. A fuse cannot be reset like a circuit breaker; they must be discarded and replaced.



To understand the operation and importance of circuit breakers, you must first understand the basics of electricity. Electricity is measured in three ways, amperage, voltage and resistance. Amperage is the number of moving electrons, the more powerful the power source, the higher the amperage. Voltage is the amount of current being "pushed" through a conductor, usually a wire. Resistance in a circuit is measured in Ohms. As the current flows through the circuit, it meets resistance, primarily the load or equipment. A circuit needs four things to function; a power source, the equipment being powered, and two wires to carry the load to and from the power source.

The electricity that enters a house comes from an electrical power grid. It is designed to enter your home at 120 volts. These electrical circuits are also grounded for protection. The electricity coming into the house meets resistance by being used. Appliances and other loads are designed to use a certain amount of current and produce a certain amount of resistance. The electricity coming in never goes directly to ground. If it were to do that, it would meet no resistance, increasing the current flow. Increased current flow can cause damage to equipment, and excessive heat. This is why the circuit breaker is used.

If for some reason, there is an increase in current flow, the circuit breaker will trip. Increased flow can be caused by many things; a bare wire touching ground or the motor of an appliance shorting to ground are examples.

The circuit breaker monitors current flow. When the current rises to a predetermined unsafe level, it will trip a switch. There are several types of circuit breakers, the most common being the bi-metal thermal circuit breaker. Two types of dissimilar metal are used and as the current flows though the circuit breaker, one of the metals expands faster than the other. As the expanding metal bends reaches the safe value it will pop "open" or will move a linkage, breaking the circuit and stopping the current flow. As the metal cools, it will be able to be popped back into place, re-energizing the circuit.

Another type of circuit breaker is the magnetic circuit breaker. As the current flow increases through the circuit breaker, the magnetic field increases. If it increases to a pre-determined value which is strong enough to move a linkage, moving a switch, it will terminate the current flow. As soon as the current is stopped, the magnetic field is weakened, allowing the circuit breaker to be manually reset.

Built into the circuitry of your home is an even more modern circuit breaker, the ground fault interrupter (GFI). The ground fault interrupter is designed to protect more than appliances and wiring. They are designed to protect one from electrocution. It uses current differential to determine if the current flow is going to ground. If one were to touch a live wire, the current would flow through the individual, directly to ground. The current that should be returning to the power source is measured against the current flowing from the power source. If the differential of the two reaches an unsafe level, the ground fault interrupter will trip, terminating the current flow through the circuit.

The circuit breakers in your home are usually centralized in one place, commonly called a circuit breaker panel. Circuits will be divided into sections of the home. Ground fault interrupters are placed in the smaller circuits of the home protecting one electrical outlet, or a series of outlets. Their reset switch is usually located on the outlets themselves.

Electricity is so common place in sour society that its danger is often overlooked. The hazards of fire or electrocution are as real now as they were one hundred years ago. The circuit breaker's simple design and ease of use has essentially mitigated the dangers that exist to us and our equipment.

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