Types of Circuit Breakers
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Types of Circuit Breakers: Classification, Working & Uses

A circuit breaker is an automatic switch that opens a circuit when it detects an overload, short circuit or earth leakage, and can be reset once the fault is cleared. Circuit breakers are classified by voltage level (low, medium, high), by arc-quenching medium (air, oil, SF6, vacuum) and by application. The most common types are MCB, MCCB, ACB, VCB, SF6 breakers, RCCB and RCBO.
This guide explains each type, how they are classified, where each one is used, and how to choose and test the right breaker.

What a Circuit Breaker Does

  • Spots overload and short circuits using thermal, magnetic, electronic, or mixed-trip logic.
  • Interrupts the fault at its rated voltage and breaking capacity (Icu/Ics) so the arc dies cleanly.
  • Goes back into service once the cause is fixed no toss-and-replace like a fuse.
  • Supports coordination with upstream/downstream devices so only the right breaker trips.

Classification of Circuit Breakers

Circuit breakers are classified in five main ways. Most engineers first split them by voltage level, then by the medium used to quench the arc.

By Voltage Level

Class

Voltage range

Common types

Low voltage (LV)

Up to 1 kV

MCB, MCCB, ACB, RCCB, RCBO, MPCB

Medium voltage (MV)

1 kV to 36 kV

VCB, SF6

High voltage (HV)

Above 36 kV

SF6 (live tank, dead tank, GIS); older air blast and oil breakers

By Arc-Quenching Medium

  • Air break (ACB): The arc is stretched and cooled in arc chutes in open air. Used in LV switchboards up to about 6300 A.
  • Air blast: A blast of compressed air blows out the arc. Once common in HV systems, now largely replaced by SF6.
  • Bulk oil (BOCB): The contacts sit in a large oil tank; the oil quenches the arc and insulates. Obsolete in new installations.
  • Minimum oil (MOCB): Uses a small volume of oil only for arc quenching. Still found in older MV and HV substations.
  • SF6: Sulphur hexafluoride gas absorbs the arc and restores insulation fast. The standard choice for 33 kV and above.
  • Vacuum (VCB): The arc is interrupted inside a sealed vacuum bottle. The standard choice from 3.3 kV to 36 kV.

By Installation

  • Indoor: Fitted in metal-clad or metal-enclosed switchgear panels, usually up to 36 kV.
  • Outdoor: Live-tank or dead-tank breakers in open-air substations, from 33 kV upward.

By Operating Mechanism

Spring-operated (most LV and MV breakers), pneumatic, hydraulic and magnetic-actuator mechanisms. Small breakers such as MCBs are switched manually and trip automatically.

By Type of Supply

Circuit breakers are either AC or DC. DC arcs have no natural current zero, so DC systems such as solar PV and battery banks need breakers with a specific DC rating.

Main Types of Circuit Breakers and Where They Fit

Type

Typical Ratings

Trip Principle

Best For

Quick Notes

MCB (Miniature Circuit Breaker)

Up to ~125 A, 240/415 V AC

Thermal-magnetic

Residential, small commercial sub-circuits

Choose curve B/C/D based on inrush: B for resistive, C for mixed, D for high inrush (motors).

MCCB (Moulded Case Circuit Breaker)

~16–1600 A, LV (up to 690 V)

Thermal-magnetic or electronic

Industrial feeders, large motors, panels

Higher breaking capacities, adjustable trip; good for selective coordination.

ACB (Air Circuit Breaker)

~630–6300 A, LV

Electronic trip, air arc-quenching

Main incomers, tie breakers in LV switchboards

Flexible protection (LSIG), draw-out designs for maintenance.

VCB (Vacuum Circuit Breaker)

MV (3.3–36 kV)

Magnetic/electromagnetic in vacuum

Medium-voltage distribution, motors

Long life, minimal maintenance, fast interruption.

SF6 Circuit Breaker

MV/HV

Gas arc-quenching

Grid, substations

High breaking performance; follow gas-handling procedures and regulations.

RCCB/RCD (Residual Current Device)

30 mA–300 mA

Differential current

People protection (earth leakage)

Trips on leakage; doesn’t protect against overload/short by itself.

RCBO (RCD + MCB)

Up to ~63 A

Combined differential + thermal-magnetic

Circuits needing both overload and earth-leak protection

Saves space, protects people, and wiring in one device.

MPCB (Motor Protection Circuit Breaker)

Up to a few hundred A

Thermal-magnetic tuned for motors

Individual motor feeders

Handles inrush, provides phase-loss, and overload protection.

Hydraulic-Magnetic Breaker

LV

Magnetic with hydraulic delay

Constant-current loads, high ambient temps

Trip point stable across temperature; useful in racks/data centers.

DC-Rated Breakers

LV/MV DC

Various

Solar PV strings, battery systems, EV DC

DC arcs behave differently—use a breaker with a DC rating, not an AC-only device.

Use this table as a starting point, then fine-tune with fault levels, selectivity, and installation standards.

Types of MCB (Trip Curves, Poles and Ratings)

MCBs are grouped by trip curve, number of poles and current rating. The trip curve decides how much surge current the MCB tolerates before it trips instantly.

MCB Types by Trip Curve

Curve

Instant trip at

Best for

Type B

3 to 5 × rated current

Lighting, heaters, resistive loads in homes

Type C

5 to 10 × rated current

Mixed loads, small motors, ACs, commercial circuits

Type D

10 to 20 × rated current

Motors, transformers, welding sets, high inrush loads

Type K

8 to 12 × rated current

Motors and transformers needing tight overload protection

Type Z

2 to 3 × rated current

Sensitive electronics, semiconductors

Types B, C and D are defined in IEC 60898-1. Types K and Z follow IEC 60947-2.

MCB Types by Number of Poles

  • SP (single pole): For single-phase circuits; switches the phase only.
  • SP+N / DP (double pole): For single-phase circuits; switches phase and neutral together.
  • TP (triple pole): For three-phase circuits without neutral switching.
  • TPN / 4P: For three-phase circuits where the neutral must also be switched.

Standard MCB Ratings

Common current ratings are 0.5, 1, 2, 4, 6, 10, 16, 20, 25, 32, 40, 50 and 63 A, and some ranges go up to 100 or 125 A. Breaking capacity is usually 4.5 kA, 6 kA or 10 kA. Always size the MCB to the cable, not just the load.

Types of RCCB

  • Type AC: Detects AC leakage only; for general residential use.
  • Type A: Detects AC and pulsating DC leakage; for appliances with electronics.
  • Type F: Adds mixed-frequency leakage detection; for inverter and VFD-driven appliances.
  • Type B: Also detects smooth DC leakage; for EV chargers, solar inverters and VFDs.
Sensitivity is 30 mA for protection of people, and 100 or 300 mA for fire protection.

MCB vs MCCB vs ACB vs VCB: Key Differences

Feature

MCB

MCCB

ACB

VCB

Voltage

LV (240/415 V)

LV (up to 690 V)

LV (up to 690 V)

MV (3.3 to 36 kV)

Current range

Up to about 125 A

About 16 to 1600 A

About 630 to 6300 A

About 630 to 4000 A

Breaking capacity

Up to about 10 kA

Up to about 150 kA

Up to about 150 kA

About 25 to 50 kA

Trip setting

Fixed

Fixed or adjustable

Fully adjustable (LSIG)

Via external protection relay

Arc medium

Air

Air

Air

Vacuum

Typical use

Homes, final circuits

Feeders, motors, panels

Main incomers, PCC panels

MV switchgear, substations

Maintenance

None; replace if faulty

Low

Periodic; draw-out design

Low; sealed vacuum bottle

Quick rule: For loads above about 100 A, move from an MCB to an MCCB. Above about 800 A, and for main incomers, use an ACB. Above 1 kV, use a VCB or SF6 breaker.

Which Circuit Breaker Is Used in a Substation?

The breaker used in a substation depends on the voltage level. Typical practice in Indian distribution and transmission substations:

Voltage level

Breaker usually used

Typical installation

11 kV

VCB

Indoor switchgear panels

33 kV

VCB or SF6

Indoor panels or outdoor

66 kV to 132 kV

SF6

Outdoor or gas-insulated switchgear (GIS)

220 kV and above

SF6

Outdoor or GIS

Station auxiliaries (415 V)

ACB, MCCB, MCB

LT panels

DC control supply

DC-rated MCB/MCCB

Battery and DCDB panels

Older substations may still run minimum oil, bulk oil or air blast breakers. Most utilities replace them with VCB or SF6 breakers during upgrades, since the older types need far more maintenance.

How to Choose the Right Breaker

  1. System voltage and frequency. Match the rated voltage and insulation level (LV, MV, or HV).
  2. Load type. Resistive, inductive, motor starting, transformers, or power electronics all have different inrush and fault signatures.
  3. Breaking capacity. Calculate prospective short-circuit current at the installation point; pick Icu/Ics accordingly with a margin.
  4. Trip curve and adjustability. For MCBs, select B/C/D curves. For MCCB/ACB, set long/short/inst/ground (LSIG) to coordinate cleanly.
  5. Number of poles. Single-pole, double-pole, three-pole, or four-pole, depending on supply and neutral switching needs.
  6. Coordination and selectivity. Ensure downstream devices trip first under downstream faults; check the manufacturer’s selectivity charts.
  7. Environment. Ambient temperature, altitude, enclosure rating, pollution degree, and maintenance access all matter.
  8. Standards and approvals. For low-voltage distribution, IEC 60898-1 (MCB for household) and IEC 60947-2 (MCCB/ACB/industrial LV) are common references. For MV/HV, look to the IEC/IEEE C37 series and utility specs.

Real World Uses of Circuit Breakers

  • Apartments, villas, small offices: MCBs for lighting and socket circuits; RCBOs in wet areas or where people protection is a must.
  • Factories and process plants: MCCBs for feeders and large motors; an MPCB on each motor branch; add RCCB/RCBO where leakage protection is required or the environment is wet, dusty, or portable-tool heavy.
  • Commercial buildings and hospitals: ACBs as main incomers and tie breakers in LV boards; MCCBs on risers and big AHUs; RCBOs on critical circuits where nuisance trips would disrupt operations or patient care.
  • Data centers and telecom: Hydraulic-magnetic breakers or electronic MCCBs to keep trip points stable as rooms heat up.
  • Utilities and campuses (medium voltage): VCBs in MV switchgear for feeders and large motors; SF6 breakers in substations where the spec calls for them follow gas-handling rules and recordkeeping.
  • Solar, storage, and EV infrastructure: Use DC-rated MCB/MCCB for PV strings, combiner boxes, battery racks, and DC fast charge; mind polarity and choose devices designed to quench DC arcs.

Installation and Safety Tips That Save Headaches

  1. Torque terminals to spec and re-torque after thermal cycling on large conductors.
  2. Test RCD/RCCB “test” buttons monthly; verify trip times during commissioning.
  3. For motors, coordinate the breaker with contactors, overloads, and soft starters/VFDs to avoid nuisance trips on start.
  4. Keep spares for critical MCCBs/ACBs and document settings; label panels so field teams don’t guess.
  5. Periodically operate and inspect draw-out breakers (ACBs/VCBs) so that mechanisms don’t seize.

Types of Circuit Breaker Testing

Every breaker is tested at the factory and again in service to confirm it will operate when a fault occurs. The main tests are:

Test

What it checks

Test equipment

Timing test

Opening, closing and CO times; synchronism between poles

Circuit Breaker Time Interval Meter

Contact resistance (CRM)

Micro-ohm resistance of the main contacts

Contact Resistance Meter

Dynamic contact resistance (DCRM)

Wear of main and arcing contacts during operation

Operational Analyzer with DCRM and CRM

Operational analysis

Travel, speed, coil current and timing in one run

Circuit Breaker Operational Analyzer

High voltage withstand

Insulation strength

High Voltage Tester

Mechanical endurance

Performance over thousands of operations

Circuit Breaker Endurance Test System

Production testing

Routine tests on the assembly line

Circuit Breaker Test System

Railway VCB testing

Timing and contact checks on locomotive VCBs

Loco-VCB Analyzer

Conclusion

Choosing among the different types of circuit breakers isn’t about memorizing acronyms. It’s matching the device to the job: voltage, fault level, load behavior, and protection goals.
Start with MCB vs MCCB vs ACB for low voltage, step up to VCB/SF6 for medium and high voltage, add RCCB/RCBO where people protection is required, and use DC-rated devices for DC systems. Get those fundamentals right and your distribution stays safe, selective, and easy to maintain.
Test Every Breaker You Build or Maintain Crest Test designs circuit breaker test systems for OEMs and on-field analyzers for utilities, covering MCB, MCCB, ACB and VCB. Talk to our team about the right test setup for your breaker range.

FAQs:

A circuit breaker is a switch that automatically opens when it detects an overload, short circuit, or earth leakage. It prevents fires, protects equipment, and reduces downtime.
MCB, MCCB, ACB, VCB, SF6 breakers, RCCB/RCD, RCBO, MPCB, hydraulic-magnetic breakers, and DC-rated breakers for PV or battery systems.
There is no single fixed number, because breakers are classified in several ways. By voltage there are three classes: low, medium and high voltage. By arc-quenching medium there are six: air break, air blast, bulk oil, minimum oil, SF6 and vacuum.
Broadly, circuit breakers are either low voltage (up to 1 kV, such as MCB, MCCB and ACB) or high voltage (above 1 kV, such as VCB and SF6). They can also be split into AC and DC breakers.
By trip curve, MCBs are Type B, C, D, K and Z. Type B suits resistive loads, C suits mixed loads, and D suits motors and transformers with high inrush current. By poles, they are SP, DP, TP, TPN and 4P.
An MCB is for lower currents and simple branch circuits, with fixed trip settings. An MCCB handles higher currents and fault levels and often offers an adjustable thermal/magnetic (or electronic) trip for fine control and selectivity.
An MCB protects wiring from overload and short circuits. An RCCB protects people from electric shock by tripping on earth leakage, but it does not protect against overload. An RCBO combines both in one device.
VCBs are used at 11 kV and 33 kV. SF6 breakers are used at 33 kV and above, including 66, 132, 220 and 400 kV substations. ACBs and MCCBs protect the station’s 415 V auxiliary supply.
An MCCB covers roughly 16 A to 1600 A, so it is the usual choice from 200 A. Above about 800 A, and for main incomers, an ACB is preferred.
Match system voltage, calculate fault current for breaking capacity, select the correct trip curve/setting, ensure coordination with upstream/downstream devices, and account for environment and standards.
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