An MCB protects small final circuits up to about 125 A, an MCCB protects feeders and larger loads from tens of amps up to around 1,600 A or more, and an ACB is the main incomer breaker for large low-voltage systems from several hundred amps to several thousand. The three differ in current rating, breaking capacity, trip unit and the standard they are tested to. This guide explains the differences so you can specify the right one.
The three breaker types in brief
MCB (miniature circuit breaker): a small, DIN-rail breaker with a fixed thermal-magnetic trip. Used for lighting, sockets and small motor circuits in homes, offices and final distribution boards. See ranked miniature circuit breaker manufacturers.
MCCB (moulded case circuit breaker): a larger breaker in an insulating moulded case, with adjustable or electronic trip settings. Used for sub-main feeders, motor control centres, large equipment and as incomers on smaller panels. See ranked moulded case circuit breaker manufacturers.
ACB (air circuit breaker): a large, often withdrawable breaker whose contacts open in air with arc chutes. It has a stored-energy mechanism and an electronic trip unit, and it is used as the main incomer and bus coupler in LV switchboards, typically after a transformer.
Side-by-side comparison
| Factor | MCB | MCCB | ACB |
|---|---|---|---|
| Typical current range | Up to 125 A | About 16 A to 1,600 A, some frames higher | About 630 A to 6,300 A |
| Breaking capacity | Lower (Icn ratings such as 6 kA or 10 kA are common) | Medium to high, by frame and version | High, with high short-time withstand (Icw) |
| Trip unit | Fixed thermal-magnetic, curves B, C, D | Thermal-magnetic (fixed or adjustable) or electronic | Electronic, fully adjustable, often with metering and communication |
| Mounting | DIN rail | Fixed, plug-in or withdrawable | Fixed or withdrawable |
| Standard | IEC 60898-1 (household and similar); some also to IEC 60947-2 | IEC 60947-2 | IEC 60947-2 |
| Selectivity category | Not applicable | Usually category A | Usually category B (with Icw) |
| Typical use | Final circuits in distribution boards | Feeders, motors, sub-main panels | Main incomers, bus couplers, generator breakers |
| Maintenance | Replace when faulty | Limited | Periodic inspection; contacts and arc chutes can be serviced |
The current ranges above are typical of what manufacturers offer; always check the catalogue frame sizes.
IEC 60898-1 vs IEC 60947-2
The standard tells you who the breaker is designed for and how its breaking capacity is defined.
IEC 60898-1 covers circuit breakers for household and similar installations, intended for use by people without electrical training. Ratings are defined at fixed values, and breaking capacity is stated as Icn (rated short-circuit capacity). The standard also defines a service breaking capacity, Ics, linked to Icn.
IEC 60947-2 covers circuit breakers for industrial use, operated and maintained by skilled persons. It defines Icu and Ics, and for category B breakers Icw. MCCBs and ACBs are tested to this standard. Many MCBs are dual-certified to both standards, and in that case the IEC 60947-2 rating at a given voltage can differ from the Icn value.
When comparing offers, make sure you are comparing ratings from the same standard at the same voltage.
Breaking capacity: Icu, Ics and Icw
- Icu (rated ultimate short-circuit breaking capacity): the highest fault current the breaker can interrupt. After an Icu test, the breaker may not be fit for further service.
- Ics (rated service short-circuit breaking capacity): the fault current the breaker can interrupt and then continue in normal service. It is stated as a percentage of Icu: 25, 50, 75 or 100 %.
- Icw (rated short-time withstand current): the current a category B breaker can carry for a stated time (for example 1 second) without tripping. This allows downstream breakers to clear faults first, which gives selectivity.
The breaking capacity must be at least the prospective short-circuit current at the point of installation. For critical feeders, choose a breaker with Ics equal to or close to Icu so it can be returned to service after a fault.
Trip units
Thermal-magnetic trip units use a bimetal for overload protection and a magnetic coil for short-circuit protection. On MCBs the settings are fixed and the magnetic trip is defined by the curve:
- Curve B: trips at 3 to 5 times rated current. For resistive loads and long cables.
- Curve C: 5 to 10 times. General use, small motors and lighting.
- Curve D: 10 to 20 times. High inrush loads such as transformers and motors.
Electronic trip units measure current with sensors and offer adjustable long-time, short-time, instantaneous and earth-fault protection (often shortened to LSIG). They are standard on ACBs and available on most MCCB ranges. Advanced units add metering, event logs and communication to building or energy management systems.
How to choose
- Find the load current and prospective fault current at each point in the system.
- Final circuits up to about 125 A with modest fault levels: MCB.
- Feeders, motors and sub-main panels, or where fault levels exceed MCB ratings: MCCB.
- Main incomers from a transformer, large bus couplers or generator breakers: ACB, usually withdrawable with an electronic trip unit.
- Check selectivity between upstream and downstream breakers using the manufacturer's selectivity tables.
- Check the assembly: breakers installed in a switchboard should be part of an assembly verified to IEC 61439. See distribution cabinets and power distribution boxes.
For earth leakage protection on final circuits, add RCDs; see residual current circuit breakers.
What to check with a Chinese supplier
Breakers are high-volume products, and counterfeit or relabelled units exist. Check:
- Registration: the 18-character Unified Social Credit Code, with a business scope that includes LV electrical apparatus.
- Factory vs trader: ask whether the company assembles and tests breakers itself, and request a video of the calibration and short-circuit test equipment.
- Standards and reports: test reports to IEC 60898-1 or IEC 60947-2 from an accredited laboratory, stating Icn or Icu/Ics at your system voltage.
- Certificates: CB scheme certificates, CE marking for Europe, CCC for China, and ISO 9001.
- Markings: confirm that the rating label matches the report and the order.
Our scores show data completeness, not product quality; see the methodology. Then see the ranked list of circuit breaker manufacturers.
Frequently asked questions
Can I use an MCCB instead of an MCB?
Yes, an MCCB can protect a small circuit if its rating and trip settings suit the load, but it costs more and takes more space. MCBs remain the normal choice for final circuits in distribution boards.
What is the difference between Icu and Ics?
Icu is the maximum fault current the breaker can break; Ics is the fault current it can break and then stay in service. Ics is given as a percentage of Icu.
Why are ACBs used as main incomers?
They handle high rated currents, have high short-time withstand ratings for selectivity, and offer adjustable electronic protection. Withdrawable versions can also be removed for maintenance without dismantling the switchboard.
Is an MCB tested to IEC 60898-1 suitable for industrial panels?
It may be, but industrial specifications usually call for IEC 60947-2 ratings. Choose MCBs certified to both standards if they will be used in industrial assemblies.