What Is a Circuit Breaker and How Does It Work?

A circuit breaker is an electrical safety mechanism specifically engineered to safeguard an electrical circuit from harm caused by an excessive flow of current that surpasses the equipment’s safe capacity (known as overcurrent). The primary purpose of this device is to disrupt the passage of electric current in order to safeguard equipment and avoid the occurrence of fire. Unlike a fuse, which functions just once and requires replacement, a circuit breaker may be reset (either manually or automatically) to continue its usual functioning.

How does a circuit breaker work?

A circuit breaker automatically opens to cut off electricity when a fault condition or fault current occurs.

Type of circuit breaker determines how it does this. Mechanical circuit breakers, like those in your home, are switches that open and close to allow electricity to flow.

Instead of mechanical components, solid-state circuit breakers employ power semiconductors like Ideal Power’s B-TRAN™ to open a circuit rapidly. This saves wear and tear and may extend the lifespan.

Components of circuit breaker

• The tripping or protective mechanism, sometimes referred to as the trip unit, activates the working mechanism in the event of an electrical malfunction.
• Operating Mechanism: The operating mechanism is responsible for either opening or closing the breaker to perform its protective function.
• Molded Frame: The molded frame is the outside casing of most breakers that provides protection and support. It provides insulation for the other components of the breaker, offering protection.
• Arc Chutes: Arc chutes are positioned near the contacts to avoid damage and minimize the impact of heat on the circuit breaker’s operation. They separate when a fault occurs.
• Contacts: There are three categories of contacts: arcing, auxiliary, and main contacts, which are utilized to guarantee the most efficient airflow within the breaker.

Types of Circuit Breakers

Various categorizations of circuit breakers may be established, depending on their characteristics, such as voltage classification, construction style, interruption type, and structural attributes.

However, there are four main mediums for circuit breakers:Oil/Air/Vacuum/Sulphur Hexafluoride

higher dielectric strength of the insulating medium enables arc quenching mechanism.

Low Voltage Circuit Breakers (V < 1000 Volts)

• Miniature Circuit Breaker (MCB) is a small device used to protect electrical circuits from overcurrents or short circuits.

The MCB, or Miniature Circuit Breaker, is a widely used kind of circuit breaker designed for low voltage use in households. The device may be manually activated and deactivated, and operates based on the principles of magnetism. The bimetallic strip within the miniature circuit breaker (MCB) detects the presence of excessive electrical current and subsequently disengages a mechanical latch. MCB is available in many variants, including kinds A, B, C, D, G, H, and K.

• Air break circuit breaker is a device used to interrupt an electric circuit by using compressed air to extinguish the electric arc that forms when the circuit is broken.

Air break circuit breakers are employed in low voltage applications and have a contact life of around 6 short circuits. There are two types of circuit breakers: conventional air break and magnetic blow-out air break circuit breakers. The air break circuit breaker utilizes high resistance interruption to extinguish arcs. Reducing the cross-sectional area and extending the length of the arc increases the resistance of the arc. The arc can be extinguished by rapidly cooling and redirecting it into the circuit breaker.

• Molded Case Circuit Breakers (MCCBs)

1. Circuit breakers are within plastic cases. Large circuit breakers for high-voltage systems.
2. Up to 1600A current and 150 KA fault levels are typical for MCCBs.
3. These circuit breakers are stronger and can take more current than MCBs.
4. MCCBs use bimetal and solenoid components, although microprocessor-based ones are preferred because to their rapid, electronic release mechanism.
5. MCBs and MCCBs come in single-pole, two-pole, and three-pole forms to satisfy electrical needs.

Medium Voltage Circuit Breakers (1 kV – 33 kV)

• Minimum Oil Circuit Breaker (MoCB): Oil circuit breakers employ transformer oil as an insulator to extinguish the arc. Oil’s 110 kV/cm dielectric strength makes it a strong dielectric medium. The arc-producing ions react with oil to release hydrogen (70-80%), methane, ethylene, and acetylene. The hydrogen bubble at the contact cools the system to assist de-ionization for the electric arc since hydrogen conducts heat well. Oil turbulence in the arc route also hinders production. These circuit breakers have a contact life of 6 short circuits and are changed often.
• Vacuum Circuit Breaker: A vacuum circuit breaker employs a medium with a pressure less than 760 mm of Mercury. Low pressures are measured in Torr (1 mm Hg). In vacuum circuit breakers, 10-5 to 10-7 Torr vacuum arc quenching medium is utilized. The medium has the highest dielectric and insulating strength among circuit breaker media. The vacuum permits microprojections to generate metal ions and an electric arc. The vacuum breaker interrupts defective current in the first cycle. Vacuum circuit breakers have a 100-short circuit contact life and no explosion risk.

High Voltage Circuit Breakers (33 kV – 220 kV)

• Air Blast Circuit Breaker: For medium, high, and extremely high voltages, air blast circuit breakers replace oil. Air blast circuits are often utilized at voltages over 110 kV. Compressed air is utilized for rapid arc quenching instead of nitrogen, carbon dioxide, and hydrogen. Using air instead of other gases minimizes circuit breaker cost and size. No fires occur because air replaces oil. Air blast circuit breakers have 25 short circuit contact lives and re-closures.
• SF6 Circuit Breaker: Sulfur hexafluoride Circuit Breakers extinguish arcs in high and extremely high voltage applications with SF6 gas. Electronegative sulfur hexafluoride gas absorbs free electrons and has strong dielectric strength. Ionization for arc production requires gas-produced negative ions, which are slower than free electrons. The same gas can be utilized after 25 short circuits with SF6 circuit breakers. Fire resistance, non-explosive, noble, and non-poisonous qualities are further features.

Difference Between Fuses And Circuit Breakers

Both options have advantages and disadvantages. A fuse is often more economical. In contrast, a circuit breaker does not require replacement after each overload and is more convenient to use without risk. Although highly improbable, there have been instances where they have become obstructed and failed to interrupt the electrical circuit.

Fuses

• It must be replaced after it has interrupted an overcurrent event.
• Has a lower initial cost
• No maintenance required
• Only opens on overcurrent events
• There is no capability for optional protective features

Circuit breakers

• May be reset after interrupting an overcurrent event
• Has a higher initial cost
• Requires maintenance
• Optional protective features (i.e. ground fault)

Read More: Circuit Breakers vs. Fuses

How to test a Circuit Breaker?

A circuit breaker can be tested using an analyzer, ohm-meter, multimeter, and others. Each circuit breaker runs differently and needs distinct tests. Tests include mechanical, thermal, dielectric, short-circuit, voltage, and resistance. A licensed electrician or engineer must choose the right procedure for safety. Circuit breakers can be tested for potential difference with a digital multimeter.

• Step 1: Dry anything around the electric panel. Also, clean the damp floor and wait.
• Step 2: open the electric panel and test the circuit breaker.
• Step 3: Screwdriver reveal the circuit breaker.
• Step 4: Turn off all gadgets and appliances connected to the circuit breaker.
• Step 5: Set multimeter to “AC voltage”.
• Step 6: Connect the multimeter’s red and black leads to the circuit breaker terminal screw (hot wire) and ground screw, respectively.
• The multimeter shows breaker screw voltage.
• Step 7: Replace the circuit breaker if the potential difference is zero.
• Step 8: Set multimeter to ohm.
• Step 9: Touch one multimeter lead to the supply and one to the screw.
• Step 10: Turn-off resistance should be nil. Replacement is needed if the circuit breaker has resistance.

Features of High Voltage Circuit Breakers

• Terminal faults: Terminal faults are those that occur at the circuit breaker’s terminals.
• Short-line faults: Short-line faults are short circuits that occur within 5 kilometers of a transmission network.
• Transformer magnetizing currents: When a transformer is powered, an inrush of current occurs, which is approximately ten times the transformer’s usual current rating.
• Capacitor bank charging: Capacitor bank charging is similar to an overvoltage scenario, and the electrical system switchgear should enable the capacitor bank to charge uninterrupted.
• Transmission line energizing: Switch gears should offer safe energizing and de-energizing of transmission lines while ensuring that the equipment attached to the line is not damaged.
• Switching of the phase sequence: The phase sequence shift has a significant impact on rotating machines, and the switchgear should ensure the safe functioning of electrical rotating equipment under such situations.

Circuit Breakers FAQs

1. Is a fuse or circuit breaker better?

Both options have advantages and disadvantages. A fuse is often more economical. In contrast, a circuit breaker does not require replacement after each overload and is more convenient to use without risk. Although highly improbable, there have been instances where they have become obstructed and failed to interrupt the electrical circuit.

2. What are the signs that my circuit breaker needs maintenance or replacement?

Be vigilant for signs of a faulty circuit breaker, such as frequent tripping, buzzing sounds, or overheating. If you notice these signs, consult a qualified electrician for maintenance or replacement.

3. Why does a circuit breaker trip?

A circuit breaker trips to interrupt the flow of electricity in an electrical circuit as a safety measure to prevent overloading or short-circuiting.

The most frequent causes of circuit breaker trips are:

• Overloading: This occurs when too much current is drawn from a circuit, for example, when multiple high-power devices are used simultaneously.
• Short circuits: A short circuit occurs when there is a problem with the wiring of an appliance leading to excessive current flow.
• Ground faults: Ground faults happen in areas with high moisture, such as kitchens and bathrooms. Ground Fault Circuit Interrupters (GFCIs) are now required by electrical code for safety.

4. How to choose a circuit breaker

Selecting a circuit breaker requires knowledge of its specifications. The main considerations are:

• Voltage rating: The circuit breaker’s maximum voltage is its voltage rating. Know how much voltage your application needs and buy a circuit breaker with enough.
• Continuous current rating: Find the amperes to determine the continuous current rating. Ampere rating indicates how much continuous current a circuit breaker can handle without overheating.
• Frequency: Consider amps to estimate your circuit breaker’s frequency. For instance, 600-amp circuit breakers can handle 50–120 Hertz. Choosing the wrong one can waste energy and heat, limiting efficiency and harming components.
• Max interrupting capacity: A circuit breaker’s max interrupting capacity must always exceed the fault current that opens it. Otherwise, the circuit breaker may be destroyed.