The circuit breaker's job is to cut off the circuit whenever the current jumps above a safe level. In the following sections, we'll find out how it does this. The simplest circuit protection device is the fuse. A fuse is just a thin wire, enclosed in a casing, that plugs into the circuit. When a circuit is closed, all charge flows through the fuse wire — the fuse experiences the same current as any other point along the circuit.
The fuse is designed to disintegrate when it heats up above a certain level — if the current climbs too high, it burns up the wire. Destroying the fuse opens the circuit before the excess current can damage the building wiring. The problem with fuses is they only work once. Every time you blow a fuse, you have to replace it with a new one. A circuit breaker does the same thing as a fuse — it opens a circuit as soon as current climbs to unsafe levels — but you can use it over and over again.
The basic circuit breaker consists of a simple switch , connected to either a bimetallic strip or an electromagnet. The image below shows a typical electromagnet design. The hot wire in the circuit connects to the two ends of the switch. When the switch is flipped to the on position, electricity can flow from the bottom terminal, through the electromagnet, up to the moving contact, across to the stationary contact and out to the upper terminal. The electricity magnetizes the electromagnet See How Electromagnets Work to find out why.
Increasing current boosts the electromagnet's magnetic force, and decreasing current lowers the magnetism. When the current jumps to unsafe levels, the electromagnet is strong enough to pull down a metal lever connected to the switch linkage. The entire linkage shifts, tilting the moving contact away from the stationary contact to break the circuit. The electricity shuts off.
A bimetallic strip design works on the same principle, except that instead of energizing an electromagnet, the high current bends a thin strip to move the linkage. Some circuit breakers use an explosive charge to throw the switch. When current rises above a certain level, it ignites explosive material, which drives a piston to open the switch. More advanced circuit breakers use electronic components semiconductor devices to monitor current levels rather than simple electrical devices.
These elements are a lot more precise, and they shut down the circuit more quickly, but they are also a lot more expensive. For this reason, most houses still use conventional electric circuit breakers. One type that can be found built directly into outlets, particularly near bathroom sinks, is the ground fault circuit interrupter , or GFCI. These sophisticated breakers are designed to protect people from electrical shock, rather than prevent damage to a building's wiring.
A special type is the engine guard, which is very common in industrial environments. Its performance is exactly the same, but it is designed to cope with the current peaks generated during the start-up of electric motors. The circuit breaker or residual current circuit breaker is responsible for protecting people from electric shocks. It works in conjunction with the earthing of all the elements of the installation.
This device is used to compare the current going into the circuit with the current coming out of the circuit. If everything is correct, they should be the same and the switch remains closed, allowing electricity to pass through. Your wife is blow-drying her hair, your daughter is ironing a shirt, and your son decides to fire up the Xbox for the few remaining minutes he has before leaving for school. And you just want a piece of toast.
You pop in the bread, push down the handle, and then comes the undeniable silence signifying that everything electrical in your home has come to a halt.
Sure, you blame the toaster and curse your house, but the tripped circuit that just shut down your power is just doing its job. The sole responsibility of any given circuit breaker in your home is to protect the electrical wiring in your house and to keep you safe.
That protection occurs when the wires in your house or in a particular zone in your house are overloaded with electrical current, causing them to heat up. Instead of transferring that heat to the appliances and electronic items plugged into your outlets, causing them to burn out and potentially resulting in a fire, the circuit breaker trips. This shuts off the electricity to the entire house or to that select zone at its distribution point.
It's important to remember that it's not the number of appliances that cause your power to stop. A house has a main electrical circuit, which is made up of several minor circuits.
This circuit within your house is powered by electricity that comes from the power plant. This is necessary since an excess in the electric charge could damage the different components of the structure. But sometimes and for various reasons, the electrical charge can increase to levels greater than what a circuit can tolerate, which can cause damage to the circuit and the devices connected to it, as well as starting a fire.
Internally, circuit breakers are basically made up of pairs of metallic contacts, both fixed and moving, in addition to an operating coil. Under normal conditions — closed circuit — these contacts are touching each other, allowing the flow of electric current. These moving contacts are held together thanks to mechanical pressure exerted by another mechanism — a spring or compressed air, for example.
This pressure on the moving contacts is possible thanks to the potential energy stored in the mentioned pressure mechanism. When an overload occurs in the electrical circuit, the operating coil is charged with energy and a plunger connected to the mechanism of the moving contacts, allows the energy stored in this mechanism to be released, allowing the moving contacts to separate as well.
As the moving contacts separate, the circuit inside the CB circuit breaker opens, interrupting the flow of current and protecting the system from further damage. When electrical current passes through an air gap from an energized component to a neutral component, a plasma discharge known as arc occurs. As an example, lightning is a very large arc, crossing atmospheric space from a cloud to the ground or to another cloud.
Arcing can also occur in household electrical wiring, but also within circuit breakers during operation, which can damage them and cause fires if the arc is not controlled. Therefore, the mechanism of circuit breakers also seeks to prevent or control, as much as possible, the generation of these electric arcs.
There are different types of circuit breaker in the market, but in general, they all work under the same basic principle already explained above. The difference between the models consists basically, in the type of mechanism used to activate the separation of the moving contacts and control the generation of the electric arc.
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