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How Does a Circuit Breaker Work? Components and Working Principle

 How does a circuit breaker work

As a homeowner or a business owner, you likely have a rough answer to the question “what is a circuit breaker?” These nifty devices are crucial in protecting your electrical systems from damage caused by electrical faults. But how does a circuit breaker work? How does it keep your electrical circuits in check?

In this guide, we will discuss everything you need to know about how circuit breakers work—including the main components (complete with a circuit breaker diagram), and the working principle.

What is a Circuit Breaker?

So, what is a circuit breaker? Simply put, a circuit breaker is a safety device that is designed to protect electrical systems from overloads, short circuits, and other electrical faults.

It senses how much current flows through the circuit. When everything is running smoothly, the circuit breaker sits patiently in its "on" position, allowing current to flow freely through the circuit. But the moment something goes awry (i.e. when the current exceeds a certain level), the breaker automatically kicks in and "trips"—shutting off power to the circuit. This prevents damage to the system, destruction of the building from fires, and injury from electrocution.

Main Components of a Circuit Breaker

To understand how circuit breakers work, we need to peek under the hood to see what makes them tick. This will give you a much easier time diagnosing problems when they occur. So, what's inside a circuit breaker that's responsible for keeping your home safe?

As shown in the circuit breaker diagram below, circuit breakers typically have four main components—the fuse, the switch, the electromagnet or bimetallic strip, and the ground fault circuit interrupter.

Circuit Breaker Diagram

Now let’s break down the circuit breaker diagram:

  1. Fuse

What is a fuse? An electric fuse is a simple safety device designed to protect electrical circuits from overloading or short-circuiting. It’s made up of a metal wire or filament that melts when excessive current flows through it.

An electric fuse works on the principle of heat transfer. When an electric current flows through a wire, it generates heat. The amount of heat generated depends on the magnitude of the current and the resistance of the wire. If the current exceeds the rated value of the wire, the heat generated will be sufficient to melt the wire, breaking the circuit (i.e., you’ll have “blown a fuse”).

The protective casing of the fuse ensures that any sparks or flames created by the melted wire are contained—preventing a fire or explosion.

  1. Switch

At the heart of every circuit breaker is a simple switch. When the switch is flipped to the "on" position, it connects the hot wire in the circuit to the two ends of the switch. This allows electricity to flow through the circuit uninterrupted from the bottom terminal, through the electromagnet, up to the moving contact, across to the stationary contact, and out to the upper terminal.

The switch is connected to either an electromagnet or a bimetallic strip, which determines the mechanism of shutting off the electrical system.

  1. Electromagnet and Bimetallic Strip

An electromagnet is connected to the switch and is responsible for breaking the circuit when necessary. As the current passes through the electromagnet, it creates a magnetic field. When the current reaches an unsafe level, the magnetic force of the electromagnet becomes strong enough to pull down a metal lever connected to the switch linkage—shutting the electricity off.

In some circuit breakers, a bimetallic strip is used instead of an electromagnet. A bimetallic strip is made up of two different metals with different rates of expansion when heated. When current flows through the strip, it heats up and bends due to the different expansion rates. If the current becomes too high, the strip bends enough to trip the switch and break the circuit.

  1. Ground Fault Circuit Interrupter (GFCI)

Circuit breaker GFCIs (Ground Fault Circuit Interrupters) are special electrical safety devices that protect people from electrical shock caused by ground faults.

Ground faults occur when electricity finds an alternate path to the ground through a person's body or equipment. Circuit breaker GFCIs monitor the flow of current in a circuit and automatically cut off the power if they sense any current leakage.

Circuit breaker GFCIs work by comparing the current flowing through the hot wire with the current flowing back through the neutral wire. If there is a difference in the current flow, it means that some current is leaking into the ground, which could be dangerous. In such a scenario, the GFCI trips and shuts off the power to the circuit, preventing electrical shock.

This is How a Circuit Breaker Works

Now that you have a good idea of the components, how does a circuit breaker work?

At the basic level, a circuit breaker works by monitoring the electrical current flowing through a circuit. If the current exceeds the breaker's rated capacity, the breaker will trip, shutting off power to the circuit.

The function of a circuit breaker is achieved through a sophisticated tripping mechanism that can operate through thermal or magnetic effects. The thermal tripping mechanism uses the heat generated by the current to bend a bimetallic strip and release the operating mechanism, while the magnetic tripping mechanism uses the magnetic field generated by the current to move a plunger and do the same.

But that’s not all, when the contacts of the circuit breaker open, an electrical arc is generated between them, which can cause serious damage to surrounding components. The arc generates high temperatures and pressures that can damage the surrounding components. The arc quenching mechanism is designed to extinguish the arc quickly and safely. This can be achieved through air blasts, oil, vacuum, or sulfur hexafluoride gas—each with its unique strengths and advantages.

What is a Circuit Breaker - The Takeaway

Circuit breakers are essential in protecting your electrical systems from damage caused by electrical faults. And now that you know how circuit breakers work, you should be in a better position to diagnose problems when they arise to ensure the safety of your electrical system.

PS: If you need expert advice on circuit breakers, reach out to our team at Circuit Breaker Wholesale. Call (800) 211-4962 for all your circuit breaker needs. 


  • Do Circuit Breakers Need to be the Same Brand as the Panel?

Not necessarily, some circuit breakers are compatible with different electrical panels. But there are some factors that you need to observe to ensure safe compatibility

  • Why Do Circuit Breakers Trip?

There are several reasons why a circuit breaker may trip. The most common causes include an overloaded circuit, a short circuit, a ground fault, a faulty circuit breaker, old or outdated wiring, and weather-related issues like lightning strikes. 

  • Can I Install a Higher-Rated Circuit Breaker to Avoid Tripping?

No, it's not recommended. The circuit breaker's rating should match the wire and device it's connected to. 

  • What are the Signs of Circuit Breaker Damage?

Faulty circuit breakers can be identified by frequent tripping, burning smells, overheating, buzzing or humming noises, flickering lights, corrosion or rust on the circuit breaker, loose connections, and damaged wires.

  • Can I Reset a Circuit Breaker Myself?

Yes, you can reset a circuit breaker by flipping the switch. However, if it trips repeatedly, it's best to call a professional

  • How Often Do I Need to Replace my Circuit Breaker?

Circuit breakers can last for years, but it's recommended to have them inspected every few years to ensure they are still functioning correctly.

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