The main types of circuit breakers are the miniature circuit breaker (MCB), moulded case circuit breaker (MCCB), air circuit breaker (ACB), residual current device (RCCB or RCD), RCBO, vacuum circuit breaker (VCB) and SF6 circuit breaker. They differ in voltage level, current rating, the fault they detect and the way they put out the electric arc that forms when the contacts open.
In a UK home you will normally find MCBs, RCDs and RCBOs in the consumer unit. Factories and large buildings use MCCBs and ACBs. Substations use vacuum or SF6 breakers, and SF6-free designs are now replacing SF6 for new equipment in Europe. The table below gives the quick answer. The rest of this guide explains each type, how they differ, how to read the ratings and what is changing.
| Type | Full name | Voltage | Protects against | Typical use |
|---|---|---|---|---|
| MCB | Miniature circuit breaker | Low | Overload, short circuit | Home and office final circuits |
| MCCB | Moulded case circuit breaker | Low | Overload, short circuit (often adjustable) | Factory feeders, distribution boards, motor circuits |
| ACB | Air circuit breaker | Low | Heavy overload, short circuit | Main incoming supply of large buildings |
| RCCB / RCD | Residual current circuit breaker / device | Low | Earth leakage (electric shock and some fires) | Socket circuits, bathrooms, outdoors |
| RCBO | RCD and MCB in one unit | Low | Overload, short circuit and earth leakage | Individual circuits in a consumer unit |
| VCB | Vacuum circuit breaker | Medium | Short circuit, overload | Substations and industrial plant |
| SF6 breaker | Sulphur hexafluoride circuit breaker | Medium and high | Short circuit, overload | Transmission substations (restricted for new EU equipment) |
Table of contents
- What Is a Circuit Breaker?
- How Does a Circuit Breaker Work?
- How Are Circuit Breakers Classified?
- By voltage class
- By arc-quenching medium
- Types of Low-Voltage Circuit Breakers: MCB, MCCB and ACB
- Miniature circuit breaker (MCB)
- Moulded case circuit breaker (MCCB)
- Air circuit breaker (ACB)
- Earth Leakage and Arc Fault Devices: RCD, RCBO, ELCB, GFCI and AFDD
- RCCB and RCD
- RCBO
- ELCB
- GFCI and AFCI (North America) and AFDD (UK)
- MCB Trip Curves: Type B, C and D Explained
- Medium- and High-Voltage Circuit Breakers
- Vacuum circuit breaker (VCB)
- SF6 circuit breaker
- Oil and air-blast breakers (legacy)
- DC, Hybrid, Solid-State and Smart Circuit Breakers
- Circuit Breaker Ratings Explained
- How to Choose the Right Type of Circuit Breaker
- Circuit Breaker Standards and Regulations
- SF6 and SF6-Free Circuit Breakers
- Circuit Breaker Market in Numbers
- Frequently Asked Questions About Types of Circuit Breakers
- What are the main types of circuit breakers?
- What are the four main types of circuit breakers?
- Which circuit breaker is used in UK homes?
- What is the difference between an MCB and an MCCB?
- What is the difference between an RCCB and an RCBO?
- What is the difference between an RCD and a GFCI?
- Is an ELCB better than an RCCB?
- What is the difference between a VCB and an SF6 circuit breaker?
- What are B, C and D type MCBs?
- Why does my circuit breaker keep tripping?
- Can an AC circuit breaker be used for DC?
- Why is SF6 being phased out?
- What is the difference between a fuse and a circuit breaker?
- Can I replace an MCB with a higher-rated one?
- Which circuit breaker is used for high voltage?
- Conclusion
- Sources
What Is a Circuit Breaker?
A circuit breaker is an automatic switch that cuts off the current when something goes wrong in a circuit. It protects cables and equipment from overload and short circuits. With extra sensing, it can also react to earth leakage and arc faults. Unlike a fuse, it can be reset once the fault has been fixed.
A breaker is also the main protective part inside switchgear, which is the full assembly of breakers, busbars, relays and enclosure. The table shows how it differs from the devices it is often confused with.
| Device | Trips automatically on a fault? | Reusable after a fault? | Main job |
|---|---|---|---|
| Circuit breaker | Yes | Yes, after reset | Detect and interrupt faults |
| Fuse | Yes (the element melts) | No, must be replaced | Interrupt overload and short circuit |
| Isolator (disconnector) | No | Yes | Give a safe, visible gap for maintenance; not made to break load current |
How Does a Circuit Breaker Work?
Every circuit breaker does three things: it senses the fault, trips its mechanism and puts out the arc. Four sensing methods are used, and many breakers combine two of them.
| Sensing method | How it works | Reacts to |
|---|---|---|
| Thermal | A bimetallic strip heats up and bends when current stays too high. | Overload (slow) |
| Magnetic | A coil pulls a plunger when current surges. | Short circuit (instant) |
| Electronic | Current transformers feed a microprocessor with adjustable settings. | Overload, short circuit, earth fault (MCCB and ACB) |
| Residual current | A ring-shaped core compares live and neutral current. Any difference means current is leaking to earth. | Earth leakage (RCD, RCBO) |
When the contacts open under load, current keeps flowing across the gap as an arc. The breaker must stop that arc quickly or the contacts will burn and the fault will continue. Each breaker type is built around one way of doing this, which is why the arc-quenching medium is a main way to classify them.
The MCB is the simplest example. Current passes through a bimetallic strip (for overload), then a coil (for short circuit), then the contacts, and any arc is pushed into a stack of metal plates called an arc chute.
How Are Circuit Breakers Classified?
One breaker can belong to several groups. An MCB, for example, is low voltage, air-quenched, overcurrent-protecting and AC. The four groupings below cover almost every breaker you will meet.
By voltage class
| Class | IEC-style range | Breakers | Where |
|---|---|---|---|
| Low voltage (LV) | Up to 1 kV AC (1.5 kV DC) | MCB, MCCB, ACB, RCD, RCBO | Homes, offices, factories, data centres |
| Medium voltage (MV) | Above 1 kV, commonly up to 52 kV (market reports often use 72.5 kV) | VCB, SF6, SF6-free | Local substations (11 kV and 33 kV in the UK), industrial plant, wind and solar farms |
| High voltage (HV) | Above the MV limit | SF6, SF6-free, vacuum at the lower end | Grid substations (275 kV and 400 kV in the UK) and power stations |
By arc-quenching medium
| Medium | How it stops the arc | Typical use | Status |
|---|---|---|---|
| Air | Arc chutes stretch, split and cool the arc in open air. | MCB, MCCB, ACB | Standard for low voltage |
| Vacuum | Contacts open inside a sealed bottle. Metal vapour condenses almost instantly and the arc dies at current zero. | Medium voltage | Dominant at medium voltage |
| SF6 gas | The gas soaks up free electrons, so the arc cannot sustain itself. | Medium and high voltage | Restricted for new EU equipment |
| SF6-free | Clean air, vacuum with natural-origin gases or other non-SF6 designs. | Medium voltage, and increasingly high voltage | Growing |
| Oil | Oil cools the arc and produces gas bubbles that help extinguish it. | Older substations | Legacy |
| Air-blast | Compressed air is blown across the contacts. | Older transmission equipment | Legacy |
The other two groupings, protection function and current type, are covered in the sections on earth leakage devices and DC breakers.
Types of Low-Voltage Circuit Breakers: MCB, MCCB and ACB
Miniature circuit breaker (MCB)
An MCB is the small, clip-on breaker you see in a consumer unit. It protects one final circuit, such as lighting or a cooker, against overload and short circuit.
- Rating: commonly 6 A to 63 A, with a breaking capacity of 6 kA or 10 kA.
- Trip: thermal-magnetic with a fixed setting, chosen by curve type B, C or D.
- Standard: BS EN 60898-1 (IEC 60898-1).
- Limit: it does not detect earth leakage, so it does not protect a person from shock.
Moulded case circuit breaker (MCCB)
An MCCB is a larger breaker in a sealed moulded casing. It handles higher currents and fault levels than an MCB, and most models let an engineer adjust the trip settings. It is used on feeders, distribution boards and machine circuits, ranging from tens of amps up to 1,600 A or more depending on the frame. MCCBs are covered by BS EN 60947-2.
Air circuit breaker (ACB)
An ACB is the heavy-duty low-voltage breaker, typically rated from about 630 A to 6,300 A. It uses an electronic trip unit with detailed settings and is often a draw-out design, so it can be racked out for maintenance. You find ACBs on the main incoming supply of large buildings, on generators and on bus-couplers in low-voltage switchboards.
| Feature | MCB | MCCB | ACB |
|---|---|---|---|
| Role | Final circuits | Feeders and machines | Main incomer, large feeders |
| Typical current | 6 A to 63 A | Tens of amps to 1,600 A or more | About 630 A to 6,300 A |
| Trip settings | Fixed | Often adjustable | Electronic, highly adjustable |
| Build | Compact, DIN-rail mounted | Moulded case | Large frame, often draw-out |
| Found in | Consumer units, small boards | Industrial and commercial panels | Low-voltage main switchboards |
| Standard | BS EN 60898-1 | BS EN 60947-2 | BS EN 60947-2 |
Earth Leakage and Arc Fault Devices: RCD, RCBO, ELCB, GFCI and AFDD
MCBs protect cables and equipment. These devices protect people and reduce fire risk, and they are the main source of naming confusion between the UK, India and the US.
RCCB and RCD
A residual current device compares the current going out on the live conductor with the current coming back on the neutral. If they differ, current is leaking to earth, perhaps through a person, and the device trips within milliseconds. A 30 mA rating is used as additional protection against electric shock. Ratings of 100 mA and 300 mA are used for fire protection or where a time delay is needed. An RCCB gives no overload or short-circuit protection, so it must work alongside an MCB. Press the test button regularly, as the manufacturer advises. For the earthing side of this protection, see our earthing and surge protection guides.
RCBO
An RCBO combines an MCB and an RCD in one unit. Fitting one per circuit means a fault trips only that circuit, instead of everything behind a shared RCD.
ELCB
ELCB is an older name. Voltage-operated ELCBs are obsolete because they can miss faults. Modern current-operated devices do the same job as an RCCB and are called RCCBs or RCDs. If your property still has an old ELCB, ask an electrician to check it.
GFCI and AFCI (North America) and AFDD (UK)
A GFCI is the North American equivalent of an RCD, built to UL 943 and set to trip at about 4 to 6 mA. An AFCI detects the electrical signature of a dangerous arc, such as one caused by a loose connection or damaged cable, which an MCB or RCD can miss. The UK equivalent is the arc fault detection device (AFDD), covered by BS EN 62606. BS 7671 requires AFDDs on socket circuits in certain higher-risk residential buildings and treats them as a recommendation elsewhere.
| Device | Overload | Short circuit | Earth leakage | Arc fault | Name used in |
|---|---|---|---|---|---|
| MCB | Yes | Yes | No | No | UK, India, IEC countries |
| MCCB | Yes | Yes | No | No | UK, India, IEC countries |
| RCCB / RCD | No | No | Yes | No | UK, EU, India |
| RCBO | Yes | Yes | Yes | No | UK, EU, India |
| AFDD | Varies | Varies | Varies | Yes | UK, EU |
| GFCI breaker | Yes | Yes | Yes | No | US, Canada |
| AFCI breaker | Yes | Yes | No (unless dual-function) | Yes | US, Canada |
| ELCB | No | No | Legacy method | No | Older installations |
These devices matter because electrical faults cause a large share of home fires. Electrical Safety First’s analysis of Home Office data puts electrical causes behind 53.4% of accidental dwelling fires in England, or 14,186 fires.
MCB Trip Curves: Type B, C and D Explained
The letter on an MCB tells you how big a current surge it will tolerate before it trips instantly. Some equipment draws a large surge for a moment when it starts. If the breaker is too sensitive, it trips for no real fault. If it is not sensitive enough, a fault may not trip it quickly enough.
| Type | Instant trip range | Suits | Examples |
|---|---|---|---|
| B | 3 to 5 × rated current | Low surge, resistive loads | Lighting, sockets, heaters |
| C | 5 to 10 × rated current | Mixed loads with moderate surge | Small motors, commercial lighting, air conditioning |
| D | 10 to 20 × rated current | High surge loads | Transformers, welders, large motors |
All three share the same thermal (overload) behaviour. Under the standard, the breaker must not trip within an hour at 1.13 times its rated current, and must trip within an hour at 1.45 times. Types K and Z are specialist curves for motor and sensitive electronic circuits, and their exact bands vary by manufacturer. When you work on motor circuits, always check the starting current against the curve.
Medium- and High-Voltage Circuit Breakers
Vacuum circuit breaker (VCB)
A VCB opens its contacts inside a sealed vacuum bottle, called an interrupter. With no air to ionise, the arc dies out at the next current zero. The sealed design needs little maintenance and uses no greenhouse gas. VCBs are the standard choice at medium voltage, from 1 kV up to about 72.5 kV, in industrial plant, wind and solar farms and distribution substations. They held 39.5% of global circuit breaker revenue in 2024. For the substation equipment around them, see our transformers and substations guides.
SF6 circuit breaker
SF6 gas has very high insulating strength, so SF6 breakers are compact and can handle high voltages. They have been the standard at transmission voltages and in gas-insulated switchgear. The drawback is climate impact, covered in the SF6 section below. Outdoor high-voltage breakers are built as live-tank designs, where the interrupter sits at line voltage, or dead-tank designs, where it sits inside an earthed metal tank. For the trade-offs between air- and gas-insulated equipment, see AIS vs GIS switchgear.
Oil and air-blast breakers (legacy)
Oil circuit breakers (bulk-oil and minimum-oil) and air-blast breakers are legacy technologies. You may still find them in older substations, but new installations use vacuum or gas designs. Oil adds fire and spill risk, and air-blast breakers need a noisy compressed-air system.
DC, Hybrid, Solid-State and Smart Circuit Breakers
DC current never passes through zero on its own, so the arc is much harder to extinguish than on AC. An AC breaker must not be used on a DC circuit unless it is rated for DC at that voltage. DC breakers use features such as magnetic blow-out, a longer arc path or electronics to force the current down. Demand is rising with solar PV, battery storage and EV charging.
| Type | How it works | Where | Status |
|---|---|---|---|
| DC breaker | Built and tested for DC; helps the arc stretch and cool without a natural current zero. | Solar PV, batteries, EV charging, DC grids | Growing |
| Hybrid breaker | A mechanical switch carries normal current; power electronics take over to clear a fault quickly. | DC systems, fast switching | Emerging |
| Solid-state breaker | Semiconductors switch in microseconds with no moving contacts. | DC microgrids, EV platforms, data centres | Niche but fast-growing |
| Smart (digital) breaker | Digital trip unit with metering and communications for remote monitoring. | MCCBs, ACBs, smart buildings | Established in larger breakers |
In the UK, BS 7671 Amendment 3 (2024) clarified how to select protective devices for circuits linked to solar PV or battery storage, and industry summaries say Amendment 4 adds a dedicated chapter on battery storage.
Circuit Breaker Ratings Explained
The markings on a breaker tell you what it can do. The two most commonly mixed up are rated current and breaking capacity.
| Rating | Symbol | What it means |
|---|---|---|
| Rated current | In | The current the breaker can carry continuously without tripping. |
| Rated voltage | Ue | The maximum voltage the breaker is designed to work at. |
| Breaking capacity | Icn (MCB), Icu (MCCB, ACB) | The highest fault current the breaker can interrupt safely. It must be at least the fault current available at its location. |
| Service breaking capacity | Ics | The share of Icu (for example 50%, 75% or 100%) the breaker can interrupt and still keep working. |
| Poles | 1P, 2P, 3P, 4P | The number of conductors the breaker switches. |
| Residual sensitivity | IΔn (in mA) | The leakage current at which an RCD or RCBO trips, such as 30 mA. |
| Trip curve | B, C, D | The instant trip range, as shown earlier. |
How to Choose the Right Type of Circuit Breaker
Choosing a breaker is a design decision for a qualified person, but these are the points they work through:
- Load type: resistive, motor, transformer or electronic. This sets the trip curve.
- Cable and rated current: the breaker must protect the cable it feeds.
- Voltage and AC or DC: the breaker must be rated for both.
- Fault level: breaking capacity must exceed the prospective fault current.
- Protection needed: overcurrent only, or also earth leakage and arc fault.
- Environment and standards: indoor or outdoor, and the rules that apply locally.
| Application | Common breaker type |
|---|---|
| Home lighting circuits | MCB with RCD protection, or RCBO |
| Home sockets and outdoor circuits | RCBO, or MCB behind a 30 mA RCD |
| Offices and shops | MCB and MCCB |
| Industrial machines and feeders | MCCB |
| Main low-voltage switchboard | ACB |
| Medium-voltage substation | VCB |
| High-voltage grid substation | SF6 or SF6-free breaker |
| Solar PV and battery storage | DC-rated breaker |
Circuit Breaker Standards and Regulations
| Standard | Covers | Region |
|---|---|---|
| BS EN 60898-1 / IEC 60898-1 | MCBs for household and similar use | UK / international |
| BS EN 60947-2 / IEC 60947-2 | Industrial low-voltage breakers (MCCB, ACB) | UK / international |
| BS EN 61008-1 and 61009-1 | RCCBs and RCBOs | UK / EU |
| BS EN 62606 | Arc fault detection devices (AFDD) | UK / EU |
| BS EN 61439-3 | Consumer units and similar boards | UK / EU |
| BS 7671 (IET Wiring Regulations) | How electrical installations are designed, installed and tested | UK |
| IEC 62271-100 | High-voltage AC circuit breakers | International |
| UL 489, UL 943, UL 1699 | Moulded-case breakers, GFCIs and AFCIs | US and Canada |
| IS/IEC 60898-1 | MCBs, adopted by the Bureau of Indian Standards | India |
| EU Regulation 2024/573 | F-gases, including SF6 in switchgear | EU |
BS 7671:2018+A4:2026 was published on 15 April 2026, and the Amendment 3 model forms were withdrawn on 15 October 2026, so Amendment 4 is now the current version. Amendments are not retroactive, but new work and inspections are assessed against the current rules. Standards texts are available from the IEC and the IET, and workplace electrical safety is covered by the Health and Safety Executive.
SF6 and SF6-Free Circuit Breakers
SF6 insulates and quenches arcs very well, but it is a powerful greenhouse gas. Its global warming potential is about 23,500 times that of CO₂ over 100 years, so even small leaks matter. EU Regulation 2024/573 restricts F-gases in new switchgear in stages.
| Voltage category | Restriction on new switchgear starts |
|---|---|
| Up to 24 kV | 1 January 2026 |
| Above 52 kV up to 145 kV, and up to 50 kA | 1 January 2028 (F-gases with GWP of 1 or more) |
| Above 24 kV up to 52 kV | 1 January 2030 |
| Above 145 kV, or above 50 kA | 1 January 2032 (F-gases with GWP of 1 or more) |
What this means in practice:
- New equipment only. Existing SF6 switchgear does not have to be removed. From 1 January 2035, servicing must use recycled or reclaimed SF6 rather than virgin gas.
- Great Britain is not bound by the EU rule. GB switchgear holds an estimated 1 million kg of SF6 across more than 200,000 units, about 97% of it on distribution networks, according to the IET. A report for the Department for Energy Security and Net Zero published in October 2026 recommends a GB phase-out broadly aligned with the EU timetable, because no definitive date has been set.
- Alternatives exist. They include dry (clean) air, vacuum interrupters and natural-origin gases. The SF6 section of our switchgear guide covers how SF6-free switchgear compares.
Circuit Breaker Market in Numbers
Demand is rising because of grid upgrades, renewables, data centres and electrification. Mordor Intelligence values the global circuit breaker market at USD 21.61 billion in 2025, growing to USD 28.36 billion by 2030. These are market-research estimates, not official statistics.
Market reports disagree widely because they define the market differently. Do not combine figures from different reports.
| Publisher | 2025 size | Growth forecast |
|---|---|---|
| Mordor Intelligence | USD 21.61 billion | USD 28.36 billion by 2030 (5.59% CAGR) |
| Meticulous Research | USD 5.86 billion | USD 12.84 billion by 2036 (7.2% CAGR) |
Frequently Asked Questions About Types of Circuit Breakers
What are the main types of circuit breakers?
The main types are MCB, MCCB and ACB for overcurrent protection, RCCB/RCD and RCBO for earth leakage, and vacuum (VCB) and SF6 breakers for medium and high voltage. Specialist types include AFDD/AFCI, DC, hybrid and solid-state breakers.
What are the four main types of circuit breakers?
By arc-quenching medium, the four classic types are air, oil, vacuum and SF6. Oil is now legacy and SF6 is being phased out for new EU equipment. For buildings, the four most common are MCB, RCD, RCBO and MCCB.
Which circuit breaker is used in UK homes?
A UK consumer unit normally holds MCBs for overload and short-circuit protection, with RCDs or RCBOs for earth leakage protection. Many new installations use an RCBO on each circuit. A qualified electrician should choose and fit them.
What is the difference between an MCB and an MCCB?
An MCB is a small, fixed-trip breaker for final circuits, usually up to about 63 A. An MCCB is larger, often has adjustable trip settings and a higher breaking capacity, and protects feeders and machines.
What is the difference between an RCCB and an RCBO?
An RCCB detects earth leakage only and needs a separate MCB for overload and short-circuit protection. An RCBO does both jobs in one device.
What is the difference between an RCD and a GFCI?
Both compare current to detect leakage. RCD is the UK and IEC term. GFCI is the North American term under UL 943, and it trips at a lower current (about 4 to 6 mA) than a 30 mA RCD.
Is an ELCB better than an RCCB?
No. The RCCB replaced the ELCB. Old voltage-operated ELCBs are obsolete, so ask an electrician to check any that are still installed.
What is the difference between a VCB and an SF6 circuit breaker?
A VCB breaks the arc in a vacuum, needs little maintenance and uses no greenhouse gas. An SF6 breaker uses a gas with excellent insulating strength but a very high global warming potential, so new SF6 equipment is being restricted in the EU.
What are B, C and D type MCBs?
They show the instant trip range: B at 3 to 5 times rated current, C at 5 to 10 times and D at 10 to 20 times. The right one depends on how much surge the load draws when it starts.
Why does my circuit breaker keep tripping?
Common causes are too many appliances on one circuit, a short circuit, earth leakage from a faulty appliance or damp, or an ageing breaker. Unplug appliances and reset it once. If it trips again, leave it off and call a qualified electrician.
Can an AC circuit breaker be used for DC?
Not unless it is rated for DC at that voltage. DC has no natural current zero, so the arc is harder to extinguish. Use breakers marked for DC.
Why is SF6 being phased out?
SF6 has a global warming potential of about 23,500 times CO₂ over 100 years. The EU is restricting it in new switchgear in stages from 1 January 2026. Existing equipment is not banned.
What is the difference between a fuse and a circuit breaker?
A fuse melts once and must be replaced. A breaker trips and can be reset, and larger breakers add adjustable settings and extra functions such as earth leakage protection.
Can I replace an MCB with a higher-rated one?
No. The rating must suit the cable and circuit. A larger breaker can let a cable overheat before it trips, so find the cause of the tripping instead.
Which circuit breaker is used for high voltage?
SF6 breakers have been standard at transmission voltages, vacuum breakers are widely used up to about 72.5 kV, and SF6-free designs are now entering high-voltage use as well.
Conclusion
Circuit breakers are grouped by voltage, arc-quenching medium, protection function and current type. In practice, MCBs, RCDs and RCBOs protect homes, MCCBs and ACBs protect larger low-voltage systems, and vacuum and SF6-free breakers protect the grid. Match the breaker to the load, the cable, the fault level and the protection needed, and leave the choice and installation to a qualified electrician.
To go further, read how breakers fit into a full switchgear assembly and how switchgear differs from a switchboard or panelboard. You can also browse our switchgear and circuit protection guides and the latest articles.
Sources
- Mordor Intelligence: Circuit Breaker Market
- Meticulous Research: Circuit Breakers Market
- Electrical Safety First: Key statistics on electrical fires
- SELECT: BS 7671 Amendment 4:2026, what is new
- Hager UK: Overview of BS 7671 Amendment 2 changes
- Electrical Safety First: Amendment 3 of BS 7671
- ABB: What you need to know about MCB trip curves
- EUR-Lex: Regulation (EU) 2024/573
- Umweltbundesamt: Factsheet on switchgear with F-gases
- ABB UK: SF6 phase-out dates
- IET: The future of British switchgear
- GOV.UK: Pathways to SF6-free distribution networks
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