How Original (MCB’s)Miniature Circuit Breaker Work

Understanding Circuit Breakers: Your Guide to Electrical Safety

An excess amount of current can flow into an electrical circuit due to factors like short circuits, overloading, component failure, power supply issues, and other causes.

As a safety measure to prevent this excess current / over voltage from damaging equipment and loads attached to the source, circuit breakers are used.

Circuit breakers simply act as a form of gate, preventing excess current from passing through the electrical circuit. They shut off the flow of current once a fault is detected, protecting electrical systems from damage and preventing potential fire hazards. In this post, we’ll break down common frustrations, desires, and fears that consumers experience and provide detailed solutions for each issue.

How Circuit Breakers Work

There are two types of operating mechanisms for circuit breakers: over toggle and two-step stored energy.

Over Toggle

The function of the operating mechanism is to provide a means of opening and closing the circuit breaker. This toggle mechanism is the quick-make, quick-break type, meaning that the speed with which the contacts snap open or close is independent of how fast the handle is moved. In addition to indicating whether the breaker is ON or OFF, the operating mechanism handle indicates when the breaker is tripped by moving to a position midway between the ON and OFF.

Two-Step Stored Energy

The two-step stored energy mechanism is used when a large amount of energy is required to close the circuit breaker and when it needs to close rapidly. The major advantages of this mechanism are rapid reclosing and safety. Rapid reclosing is achieved by storing charged energy in a separate closing spring. Safety is achieved by providing remote charging of the spring. The two-step stored energy process is designed to charge the closing spring and release energy to close the circuit breaker. It uses separate opening and closing springs. This is important because it permits the closing spring to be charged independently of the opening process. This allows for an open-close-open duty cycle. The closing spring can be charged (or recharged) manually via a charging handle or electrically via a motor. The motor can be operated remotely, allowing maximum safety for the operator.

Types Of Circuit Breakers

There are different circuit breakers used on different power systems, from residential to commercial, to industrial areas. Circuit breakers can be classified based on different features like voltage class, construction type, and how they interrupt currents.

Low-voltage Circuit Breakers (below 1,000 VAC): These are commonly used in homes, commercial, and industrial settings. They include:

• Miniature Circuit Breakers (MCB): These are small and protective circuits with a current rating of up to 125 amps.
• Molded Case Circuit Breakers (MCCB): These can handle currents up to 1,600 amps and are adjustable for higher-rated units.
• Direct-Current (DC) Breakers: Specially designed for DC applications like subway lines, these handle continuous arcs by using a blow-out coil that creates a magnetic field to control the arc.
• Solid-State Circuit Breakers (SSCB): These digital circuit breakers work faster and last longer. They use advanced electronics to interrupt currents, which makes them more efficient than mechanical breakers.
• Magnetic Circuit Breakers: These use an electromagnet to pull the contacts apart when the current is too high. They’re widely used in the U.S.
• Thermal-Magnetic Breakers: These combine both thermal and magnetic elements to react to different types of over currents. The thermal part handles long-term overloads, while the magnetic part reacts quickly to large surges.
• Magnetic-Hydraulic Breakers: These use a solenoid to open contacts and include a hydraulic delay to handle short surges like motor startup without tripping immediately.
• Common-Trip Breakers: These break multiple circuits simultaneously, ensuring that all live wires are interrupted when one trips. This prevents dangerous conditions where parts of the system might still be live even though it appears off.
• Shunt-Trip Units: These breakers are triggered remotely by an external signal, commonly used to cut power during emergencies like fires or floods.

Medium-Voltage Circuit Breakers (1-72 kV): Used in substations or switch gear, these breakers control electricity distribution in medium-voltage systems. They use vacuum or SF6 gas to extinguish the arc created when breaking the circuit.

High-Voltage Circuit Breakers (above 72.5 kV): These breakers manage power transmission. They use various mediums like oil, air, vacuum, or SF6 gas to control arcs during circuit interruptions. High-voltage direct current (HVDC) breakers are still in development but would be used to interconnect transmission systems.

Disconnecting Circuit Breaker (DCB): Combines the disconnecting and circuit-breaking functions, reducing space and increasing reliability in substations.

Smart Circuit Breakers: These are new types of breakers that allow remote monitoring of appliances and can be controlled via apps to manage energy usage, especially during high grid loads.

Other Breakers: Include residual current devices that detect small faults, arc-fault circuit interrupters for loose wires, and reclosers that automatically reset after a fault.

Important Ratings To Consider When Choosing A Circuit Breaker

• Handle Rating
• Frame Size
• Sensor/Plug Rating
• Short Circuit Current Rating
• Applicable Voltage
• Trip Functions And Settings (For More Advanced Breakers)
• ANSI, NEMA & IEC Standards applicable to your intended application

Common Frustrations When Choosing Circuit Breakers And Their Solutions

Many consumers lack a deep understanding of circuit breakers. Terms like amperage and voltage rating can be confusing, making it difficult to select the right product and many circuit breakers come with technical details like interrupting capacity or trip curve, which can be overwhelming for non-experts. Educating yourself on the basics of circuit breakers is the best way forward. Here are some important terms to understand:

• Amperage (Amps): This refers to the maximum amount of electrical current a circuit breaker can handle before it trips. Ensure the breaker’s amperage matches the circuit’s needs.
• Voltage Rating: The voltage rating indicates the maximum voltage the circuit breaker can handle. Check your system’s voltage and match it with the breaker’s rating.
• Interrupting Capacity: This is the maximum current the circuit breaker can safely interrupt without damage. Choose a breaker with an interrupting capacity higher than the potential fault current in your system.
• Trip Curve: This refers to how quickly a circuit breaker reacts to overloads. A quicker trip curve means the breaker will interrupt the flow faster in the event of an overload. For residential use, standard trip curves (type B or C) are typically sufficient.

By learning these terms, consumers can make informed decisions about which circuit breaker to choose and if these terms feel complicated, consult with an electrician or vendor for clarification on your specific needs.