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    How Do Circuit Breakers Work?

    A circuit breaker is a vital part of any electrical system. Circuit breakers protect homes from various electrical hazards (such as fault or overload) and interrupt the power whenever the electrical current becomes unsafe. Remember that time everything shut off when we had many power tools plugged in, along with the radio, work lights, and chargers? Bingo! We may work with them regularly, but many of us do not understand how circuit breakers work. Have you ever wondered how circuit breakers do all of this? Continue reading this article to unveil the answer!


    What is a Circuit Breaker

    A circuit breaker is a type of electrical switch designed to protect a circuit by heating up and cutting power when current levels exceed safe amounts and become a hazard. Doing so helps prevent damage, injury, and even fire! There are many types of circuit breakers in which features vary per the specifications and requirements for that design.


    Some instances that may occur where a circuit breaker offers protection include short circuits and overload. A circuit overload may be experienced in scenarios when too many appliances or power tools, as mentioned earlier, are plugged into one circuit. A short circuit may happen when electricity flows along a path it is not supposed to. 


    How Do Circuit Breakers Work?

    We have now considered what a circuit breaker is, and why they are so important to us. How do they work? In order to understand how circuit breakers function, we need to talk about some basics of electricity first! 


    How Electricity Works and What’s a Circuit

    Most of us depend on electricity and cannot imagine going without it, as long as we aren’t trying to live off-grid. Despite this, not all of us understand how electricity works. 


    You probably remember from science class that all matter is made up of atoms, and electrons are contained inside those atoms. Electricity is the flow of electrical charge from one atom to another. The electricity that we use is called a secondary energy source because it is generated from a primary energy source such as natural gas or coal. 


    It is good to know some basic terms when dealing with electrical circuits. The ampere (amps) are used when measuring the electrical current flowing through the circuit. Volts are the amount of pressure (aka voltage) within an electrical circuit. Electrons can flow through pretty much anything, but how easily they flow is called resistance. When resistance is measured, it is done so using units of measurement called ohms. Electrical power is measured using watts, which you get after you multiply the total amount of volts by the number of amps. 


    An electrical circuit always contains a source of power, with a positive and negative terminal. The power source pushes electrons out through a conductor, which is a material that allows the flow of electrical current, such as a copper wire. The current flows from the source to the load (what you are powering) and then back to the source in a consistent cycle. 


    Basic design of a circuit breaker

    Circuit breakers interrupt the flow of electrical current when it exceeds a predetermined amount, which is where a circuit breaker’s ratings come into play. Circuit breakers are rated based on the amount of current that they can safely carry and the amount they can safely interrupt. There are a few kinds of circuit breakers, but they all typically have these components in common.



    The frame is the outer shell of a circuit breaker usually made up of molded insulating materials. This protects the components on the inside and anything on the outside of the breaker if a hazard occurs. 



    The terminal is a block of metal with a bolt emerging on the outside of it. Wires that carry electrical current from the power supply, through the breaker, and to a load are connected here. 



    The lever (switch) is connected to the trip unit and allows a breaker to be flipped on or off. When a circuit breaker trips, the lever will be positioned in the middle to quickly identify which one needs troubleshooting.



    The contacts are two pieces of metal that move to close or open (interrupt) the circuit. One contact is attached to the actuator mechanism, while the other is connected to the main panel.


    Actuator Mechanism

    The actuator mechanism is a metal arm inside the circuit breaker. One end is attached to the lever, and the other is attached to a contact. When the lever is flipped, the actuator mechanism forces the contacts together or pulls them apart. 


    Trip Unit

    A trip unit is a part that tells the breaker when to trip automatically in the event of an overload, short circuit, or fault. 


    How Does a Circuit Breaker Work Then?

    When the lever of a circuit breaker is switched to the “on” position, it allows electricity to freely flow from the power supply (typically the electrical panel or main) through the trip unit, contacts, and out the upper terminal to power the loads on a circuit. 


    A thermal magnetic trip unit’s bi-metallic strip overheats in an event such as overload, causing it to bend and open the circuit (automatically cutting off power). During a fault or short circuit, the electromagnetic force causes the contacts inside the circuit breaker to separate, tripping the breaker and shutting off the power to the circuit with the issue.


    What Are the Common Causes of a Circuit Breaker Tripping?

    Circuit breakers trip and interrupt the power supply when it detects a problem within the circuit. What are some potential dangers that would cause a circuit breaker to trip? 


    Overloaded circuits: Overloaded circuits are the most common reason why circuit breakers trip. This happens when there is too much on one circuit, and everything is demanding more of a load than the circuit can safely carry. 


    Short Circuit: Short circuits happen when a “hot” and “neutral” wire come into contact with each other. This can be dangerous and generates a lot of heat, therefore tripping a breaker. It can be caused by many things, such as a loose connection, and you can usually smell it when it happens!


    Ground fault surges: Similar to a short, ground fault surges happen when a “hot” comes into contact with a ground or the metal on a box connected to a ground. This causes a surge of electricity that is more than the circuit can safely handle and trips the breaker.


    Arc fault: An arc fault is a spark that can happen due to loose terminals or bad connections. An arc will cause an AFCI breaker to trip to prevent overheating and fire. 


    What can you do?

    Keep in mind that many common causes for tripping breakers are preventable. Be aware of how many loads you have pulling power from the same circuit, ensuring that it doesn’t exceed the safe amount. Many of these causes can happen from poor connections, faulty wiring, or old hardware. It is always wise to double-check to ensure all parts are secure so that a circuit breaker doesn’t have to come to the rescue in the first place!



    Circuit breakers are designed to protect our electrical circuits from danger caused by an electrical hazard such as circuit overload. They are designed with a rating, which tells us how much electrical current that breaker can carry or interrupt safely. There are many kinds of breakers, but most breakers have some main components in common. The frame protects what’s inside, a terminal where wires are connected, a lever to flip the breaker on or off (and show us when a breaker has tripped), contacts that move to open or close the circuit, actuator mechanisms, and trip units. All pieces work together, and when the amount of electrical charge exceeds safe amounts, they interrupt the current. Many electrical hazards can be prevented, so ALWAYS double-check that there are not too many loads on one circuit, and look for any loose connections or outdated hardware! After taking a closer look, circuit breakers are pretty cool! The fact that they help keep us safe from injury or fire is just an added bonus.