Circuit Breaker Types: How to Identify Circuit Breakers

There are several instances where a mishap might occur when using or working with electricity. It damages houses, offices, industries, schools, and buildings. Breakers can prevent structure fires and electrocution. As an additional precaution step, it’s also essential to identify circuit breaker types.

There are two common types of breakers:

  • Miniature Circuit Breakers (MCB) are found in most residential and small commercial buildings. This type of breaker has two ways to trip; thermal overload and magnetic trip.
  • Molded Case Circuit Breakers (MCCB) are found in larger homes, commercial, or industrial applications where a high amperage is used. MCCB has a magnetic trip only and usually can be repaired if needed.

Within both MCB and MCCB breaker types are several classes of circuit breakers. Types and classes vary between residential and industrial buildings. This article will discuss the different types of circuit breakers available on the market. 

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What is a Circuit Breaker?

A circuit breaker is a safety device with an amp rating that either energizes or de-energizes a circuit through a switch.

Miniature circuit breakers, aka standard circuit breakers, have two ways to trip the circuit:

  • Thermal Overload: a thermal overload occurs when a gradual rise in both temperature and amperage occurs between 100% and 135% of the circuit’s capacity. For example, a thermal overload on the 20amp breaker occurs at 27 amps. A 60 amp breaker would experience a thermal overload at 81 amps.
  • Magnetic Trip: a magnetic trip occurs when a sudden surge of current hits the circuit. The magnetic contacts separate when this occurs immediately tripping the breaker and de-energizing the circuit.

Within the miniature circuit breaker family are breakers with sensors and microprocessors such as arc fault, combination arc fault, and ground fault circuit breakers.

  • Arc-Fault Circuit Interrupter (AFCI) is a miniature circuit breaker that has a microprocessor that monitors the electrical current and is programmed to trip when a series arcs.
  • Combination Arc-Fault Circuit Interrupter(CAFCI) is much like the arc-fault breakers but they will trip for both series and parallel arcs.
  • Ground Fault Circuit Interrupter (GFCI) is a miniature circuit breaker that detects electrical imbalances across the hot and neutral wires which occur when electricity exits the circuit in an unnatural way.

Most molded case circuit breakers are only magnetic trip breakers and are composed of parts that you can repair. These are common in larger commercial or residential applications where a large amount of electricity is needed.

Other lesser-known types of circuit breakers include shunt breakers and smart breakers.

Shunt breakers allow circuits to trip remotely, such as the other side of a room. An example of this is a breaker that controls an oversized hood and suppression system in restaurant kitchens where the breaker needs to be tripped remotely in the event of a fire.

Smart breakers allow a monitoring station to monitor and remotely control breakers through low-voltage wiring. An example of this includes where Big Box stores, for example, can receive notifications of electrical power outages in a location thousands of miles away.

How do Circuit Breakers Function?

Now that we understand what a circuit breaker is, it’s time to explain its working principle. If you have a circuit breaker in your home, it will help you understand its functionality. 

Many older houses still have fuse boxes with fuses. However, electrical panels (aka a breaker box) use circuit breakers instead of fuses. You can’t use fuses inside breaker boxes and vice versa. A breaker can trip and be reset. Fuses are sacrificial, meaning you have to replace them when they fail.

Also, a circuit breaker does not have an internal fuse. It works by internal springs and contacts that open and close to control the flow of electricity.

A circuit breaker functions through two electrodes, one being movable while the other being static. When the electrodes get into contact, the circuit becomes closed. When a circuit breaker trips, it forces the contacts to separate, which opens the circuit. A thermal overcurrent or magnetic overcurrent protection can trip a breaker in residential circuit breakers.

Assuming that the circuit is in a closed state for you to create a circuit, the logical indicator will stimulate the trip relay that disconnects the contacts when arcing occurs. 

However, when several contacts are together, there is a huge temporary potential variation between the connections that enable significant electron transition from a high to low potential. The temporary gap creates a dielectric that allows electrons to move from one electrode to another. 

Electrons move from one electrode to another when the potential variation becomes more than the dielectric strength. It will ionize the dielectric mode, leading to a big ignition between the two electrodes. The ignition is referred to as ARC. 

Even if the ignition was to last only for a few seconds, it could damage the whole circuit breaker device, translating into damage to the entire casing and equipment. 

To prevent the ignition from taking place, you must extinguish the dielectric that separates the electrodes beforehand. 

Why Arcs Occur

You should closely monitor the arc during the operation of a circuit breaker. Arcing usually occurs during faulty cases. The arc leads to a minimal resistance path resulting in a substantial current flow. Electricity is always looking for a way to ground itself and the path of least resistance.

Arcing occurs when the electricity comes in contact with a conductor that causes it to deviate from its intended path.

Arcing damages the functionality of a circuit breaker. The arc happens for the following reasons:

  • Ionized particles between the two electrodes
  • The potential variation between the electrodes

Repeated arcing will eventually cause the breaker to fail.

Types of Low-Voltage Standard Circuit Breakers

Low-voltage circuit breakers handle voltages of less than 1000 volts.

A standard breaker is a low-voltage circuit breaker installed inside circuit breaker panels that control the flow of electrical current in an electrical circuit. These can be either double-pole or single-pole breakers.

Single-Pole Circuit Breaker

Single-pole breakers (individual breakers) have the following features:

  • They project single energized wire
  • They are employed mostly in outlets, lights, and small household appliances
  • They provide 120V to the circuit
  • They have the potential of holding 15A to 30A

Single-Pole Circuit Breakers monitor the single circuit current (120-volt). They trip when there is an overload, surge, or short circuit. It consists of one live wire with a neutral wire. 

Ground Fault Circuit Interrupter Breakers (GFCI Circuit Breakers) protect against a line-to-ground fault. They are the ones that electricians install in wet rooms such as laundry rooms, kitchens, and bathrooms. They protect you from electrical shocks when a current overload occurs.

Arc Fault Circuit Interrupter Breakers (AFCI Circuit Breakers) protect against electrical arcs. Arcs usually spark immense heat, thus burning other elements like wood and other insulators. They trip when the electrical wiring detects the arcing.

Combination Arc-Fault Circuit Interrupter Breakers (CAFCI) protect against all types of electrical faults. Electricians now use CAFCI breakers where the local codes require both arc-fault and ground-fault protection.

Double-Pole Circuit Breaker

They have the following features:

  • They protect two energized wires
  • They are mostly applied in appliances such as ranges, dryers and heaters
  • They provide 240V to the circuit
  • They have the potential of holding 30 to 200 amps

Double-Pole Breakers monitor double circuit current (240 volts total). Usually, one large breaker sits across two breaker spaces inside electrical panels.

Types of High-Voltage Circuit Breakers

High-voltage circuit breakers handle 1000 volts or higher volts in commercial or industrial applications.

Air Circuit Breaker

The air circuit breaker operates in the air. The quenching medium here is an arc that is at atmospheric pressure. In most countries, this divide is replaced by oil circuit breakers. 

You can employ an air circuit breaker in a situation where the voltage ratings are 15KV. An oil circuit can’t be used because it can catch fire in such a case. 

The available types include: 

  • Plain air circuit breaker
  • Airblast circuit breaker 

Plain Air Circuit Breaker

This type of circuit breaker refers to a cross-blast circuit breaker. The device has a chamber (arc chute) that encircles the contacts.  

An arc chute is designed from the refractory material and helps cool the air circuit breaker. It has several compartments with many divisions that are separated by metallic plates. The metallic separation behaves as an arc splitter while the small compartments act as a mini-arc chute. 

When the arc splits into several arcs, all the arc voltages become higher than the system voltage. It’s therefore ideal for low voltage applications. 

Airblast Circuit Breaker

The airblast circuit breaker is ideal for 420kV, 245kV, or more system voltages. There are at least two types of airblast circuit breakers:

  • Axial blast
  • Axial blast having a sliding moving contact

Summary of Air-Blast Circuit Breakers

ProsCons
It’s small in sizeIt needs additional maintenance
It’s risk-free from fireThe air has a lower extinguishing property
It has lesser arc energy, thus perfect when a frequent application is necessary.It has a high capacity air compressor
The arc quenching is faster There is the likelihood of air pressure leakage at the air pipe junction
It needs less maintenanceThere is the likelihood of a high rise of the rate voltage chopping and restriking current
The circuit breaker has a higher speed
The arc has a constant time duration for all current values

Uses And Applications Of Air Circuit Breaker

  • It is employed in both high and low voltages and currents applications
  • It’s applied in GND and electricity sharing electrical systems of about 15KV
  • It’s useful for the protection of generators, capacitors, transformers, plants, and electrical machines

SF6 Circuit Breaker

Here, the contacts that carry current operate in sulfur hexafluoride gas. It has a high electro-negativity and excellent insulating property.

There is a negative ion form when the SF6 gas molecule collides with a free electron. 

The negative ions generated here are heavier than free electrons. The mobility of charged particles in SF6 is generally less. The mobility of charged particles is critical in conducting current via gases. 

It, therefore, means that less mobile charged and heavier particles in SF6 gas require a higher dielectric strength. The gas has a low gaseous viscosity, thus providing a good heat transfer. 

These circuit breakers are 100 times more efficient when it comes to arc quenching compared to air circuit breakers. It’s therefore ideal in high and medium-voltage electrical systems of between 33KV to 800KV. 

Types Of SF6 Circuit Breakers

  • A single interrupter circuit breaker is used for up to 220V
  • Two interrupters circuit breakers are used for up to 400V
  • Four interrupter circuit breakers are used for up to 715V

Vacuum Circuit Breakers

In a vacuum circuit breaker, a vacuum employs to extinguish the arc. It boasts an excellent interruption, dielectric recovery character, and an ability to interrupt high-frequency current. 

The vacuum circuit breaker has two electrodes that remain closed under normal operation conditions. If a fault occurs in the system, the trip coil in the breaker will energize, leading to the contact getting separated.

Advantages of Vacuum Breakers Include:

  • It doesn’t produce any noise
  • They are compact, long life and reliable
  • They can interrupt a fault current
  • It doesn’t cause any fire hazards
  • It offers a high dielectric strength
  • You’ll need less power for operation and control purposes

Oil Circuit Breaker

Oil circuit breakers use mineral oil because it offers better insulating properties than air. 

The fixed and moving electrodes are placed in the insulating oil. When the current is separated, the arc is decomposed and vaporized in hydrogen gas, thus creating a hydrogen bubble on the arc.

The high compressed gas bubble over the arc restricts the restriking of the arc. However, the oil circuit breaker is an old-school type of breaker. 

There are at least two types of this breaker:

  • Minimum oil breaker
  • Bulk oil breaker

Bulk Oil Circuit Breaker (BOCB)

Here, oil is employed to arc the breaker’s quenching media. It’s also used for insulating media between the current-carrying contacts and the earth sections of the circuit breaker. 

The working principle of this breaker states that when current-carrying contacts are separated in the oil, the arc develops between the contacts. The established arc generates a rapidly growing gas bubble on the arc.  

Moving contacts move away from fixed ones resulting in the arc’s resistance increasing. An increased resistance will lead to a reduction in temperature. There’ll therefore be a reduction in gas formation around the arc.

The arc quenching in the circuit breaker happens when the current passes through the zero-crossing. An increase in pressure increases the deionization of the gas around the arc, thus leading to arc quenching. Hydrogen gas, therefore, assists in cooling the arc quenching for this circuit breaker. 

Summary of Bulk Oil Circuit Breakers

ProsCons
The oil offers high dielectric strength.It has a long arcing time
It has one of the best cooling properties due to decomposition.It doesn’t allow a high interruption speed
It provides insulation between the live parts and the earth.
The oil absorbs arc energy while it decomposes.

Minimum Oil Circuit Breaker

This breaker uses oil as its interrupting media. The good thing about this circuit breaker is that it requires less oil. 

Summary of Minimum Oil Circuit Breakers

ProsCons
It needs a smaller spaceOil usually deteriorates due to carbonization
It needs less maintenanceIt has a high chance of experiencing fire or explosion
It’s ideal for both manual and automatic operationCarbonization increases due to its small oil quantity
Its breaking capacity cost is lessIt isn’t easy to remove gases from the spaces found between the contacts

Further classifications depend on different types, as we’ll see below:

Based on Voltage Class

The circuit breakers are mainly classified depending on the voltage that they utilize. Here, there are two types: 

  • Low Voltage: They are used primarily for voltages that fall below 1000V
  • High Voltage: They are used where the voltage is above 1000V

Based on Installation Type

Circuit breakers can also be grouped based on the installation location, either open or enclosed-air locations. They are applied at extremely high voltage levels. Enclosed circuit breakers are used internally in a building. 

However, the internal designs, such as functionality and current holding equipment, are the same. 

Depending on the Type of External Design

There are two types of circuit breakers under this category and include:

Live tank type: The switching equipment is placed at the maximum potential in the vessel. It’s also enclosed using interrupters and shielding mediums. This type is common in Asia and Europe. 

Dead tank type: The switching equipment is found at the base potential in the vessel. It’s also enclosed using interrupters and the shielding medium. They are primarily used in the United States.

Depending on the Interrupting Medium

It is a critical categorization and grouping of circuit breakers. They are classified based on the interruption medium and arc destruction approach. 

In most cases, air and oil are employed as interruption mediums. There are also vacuum and Sulphur Hexafluoride acting as interruption mediums. 

HVDC Circuit Breakers

It’s a switching device that blocks the general current flow in a circuit. When there is damage, it forms a gap between the mechanical contacts, thus forcing the circuit breaker into an open condition. 

The circuit-breaking here is somehow complicated since the current flow is unidirectional. The critical application of this breaker is to block the high voltage range of direct current ratings in the circuit. 

Conclusion

We hope you now fully understand the different types of circuit breakers for low-voltage and high-voltage applications. 

While selecting the best circuit breaker for your home or office, it would be best to consider various factors, including the design type, voltage load, and mounting style. If in doubt, contact a qualified electrician. 

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Hubert Miles

I've been conducting home inspections for 17 years. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and FHA 203k Consultant. I started HomeInspectionInsider.com to help people better understand the home inspection process and answer questions about homeownership and home maintenance.
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