Types of Circuit Breakers: MCB, MCCB, RCCB, ACB, VCB

Circuit Breaker Classification: The Complete Hierarchy

Circuit breakers are the most critical protective devices in any electrical installation. They automatically disconnect a circuit when current exceeds safe levels — protecting cables, equipment, and most importantly, people. But "circuit breaker" is a broad category that includes devices ranging from a $3 MCB in a home distribution board to a $50,000 SF6 breaker in a 220 kV substation.

This guide classifies and explains every major type of circuit breaker, organized by voltage class and function. Whether you are an engineer specifying protection for a new building, a procurement manager sourcing switchgear, or a student learning power systems, this is the reference you need.

Circuit Breaker Types at a Glance

MCB — Miniature Circuit Breaker

The MCB is the most widely manufactured circuit breaker in the world. Every home, office, and retail store contains MCBs in its distribution board. Their function is straightforward: protect individual circuits (lighting, socket outlets, appliances) from overload and short-circuit faults.

How an MCB works

Every MCB contains two protection elements:

• Bimetallic strip (thermal): Heats and bends under sustained overcurrent, mechanically releasing the trip mechanism. Provides inverse-time overload protection — higher overloads trip faster.
• Electromagnetic solenoid (magnetic): A coil generates a magnetic force that instantly trips the mechanism when fault current exceeds the magnetic threshold (defined by the B/C/D curve). Operates in under 10 ms for high-magnitude faults.

MCB trip curves

Key specifications: Rated per IEC 60898 (residential) or IEC 60947-2 (industrial). Current range 1-125 A. Breaking capacity 6-10 kA. DIN rail mounting (18 mm per pole).

For a detailed MCB vs MCCB comparison, see our dedicated guide.

MCCB — Molded Case Circuit Breaker

MCCBs bridge the gap between MCBs and ACBs. They handle higher currents and fault levels than MCBs while being more compact and economical than ACBs. MCCBs are the backbone of industrial power distribution — every factory, warehouse, and commercial building uses them for feeder protection.

What makes MCCBs different from MCBs

• Higher current range: 16 A to 2,500 A (vs MCB's 125 A maximum)
• Higher breaking capacity: 18 kA to 200 kA at 400 V (vs MCB's 10 kA)
• Adjustable trip settings: Both thermal and magnetic thresholds can be adjusted to match specific circuit requirements
• Electronic trip option: LSIG (Long-time, Short-time, Instantaneous, Ground fault) programmable protection
• Accessories: Motorized operators, auxiliary contacts, alarm switches, undervoltage releases, shunt trips

For the ACB vs MCCB decision, see our comparison guide. For sizing assistance, see our circuit breaker sizing guide.

ACB — Air Circuit Breaker

ACBs are the largest and most capable low-voltage circuit breakers. They serve as main incoming breakers, bus-tie breakers, and generator breakers in switchboards. The name "air circuit breaker" indicates that the arc is extinguished in free air using arc chutes — metal plates that split and cool the arc until it extinguishes.

Key characteristics of ACBs

• Current range: 800 A to 6,300 A
• Breaking capacity: 42 kA to 150 kA at 440 V
• Draw-out mounting: The breaker can be withdrawn from its cradle for maintenance without disconnecting cables — essential for main breakers that cannot be de-energized for servicing
• Category B per IEC 60947-2: ACBs include short-time delay (S function) for time-graded selective coordination
• Full LSIG electronic trip: All ACBs use electronic trip units with comprehensive protection functions
• Communication: Many ACBs support Modbus, Profibus, or Ethernet for integration with building management systems

NAIJI Electric integrates ACBs as incoming and bus-coupler devices in our SLVA low-voltage switchgear panels.

RCCB — Residual Current Circuit Breaker

An RCCB (also called RCD — Residual Current Device, or GFCI/GFI in North America) protects against earth leakage faults — situations where current flows through an unintended path to ground, such as through a person's body or through damaged cable insulation.

How an RCCB works

The RCCB uses a toroidal current transformer that encircles all live conductors (phase and neutral). Under normal conditions, the magnetic fields from the outgoing and returning currents cancel each other out — the net flux in the toroid is zero. When current leaks to ground (through a person, through damaged insulation, through moisture), the returning neutral current is less than the outgoing phase current. This imbalance creates a net flux that induces a voltage in the sensing winding, which triggers the trip mechanism.

Sensitivity ratings

Critical limitation: An RCCB provides no protection against overcurrent. It will not trip on overload or short circuit. An RCCB must always be installed in series with an MCB or fuse that provides overcurrent protection. This is why RCBOs exist — to combine both functions.

RCCB types (by waveform sensitivity)

• Type AC: Detects sinusoidal AC residual currents only. The basic and most economical type. Not suitable for circuits feeding electronic equipment (VFDs, UPS, LED drivers) that may generate pulsating DC residual currents.
• Type A: Detects sinusoidal AC and pulsating DC residual currents. Required by modern electrical codes (IEC 60364) for circuits feeding electronic loads. Increasingly the default specification.
• Type B: Detects AC, pulsating DC, and smooth DC residual currents. Required for EV charging stations (Mode 3 chargers), VFD-fed motor circuits, and photovoltaic inverters. More expensive but essential for these applications.
• Type F: Specifically designed for circuits with frequency-controlled drives (VFDs), handling mixed-frequency residual currents.

RCBO — Residual Current Breaker with Overcurrent Protection

An RCBO combines the earth leakage protection of an RCCB with the overcurrent protection of an MCB in a single device. It is essentially an "MCB + RCCB in one body."

Why use an RCBO instead of separate MCB + RCCB?

• Individual circuit protection: Each circuit gets its own RCD protection. If one circuit develops an earth fault, only that circuit's RCBO trips — all other circuits remain energized. With a shared RCCB protecting multiple MCBs, any earth fault trips all circuits downstream of that RCCB.
• Easier fault finding: When an RCBO trips, you immediately know which circuit has the fault. With a shared RCCB, you have to disconnect circuits one by one to find the faulty one.
• Space saving: An RCBO is typically 2 modules wide (36 mm), compared to 2 modules for the RCCB + 1 module for the MCB = 3 modules total for the separate approach.

Key specifications: Current ratings 6-40 A (matching MCB ratings). Sensitivity 30 mA (personal protection). Trip curves B or C. Breaking capacity 6 kA or 10 kA. Available in Type A, Type B, and Type F variants.

The trend in modern residential and commercial installations is strongly toward RCBOs for every circuit rather than shared RCCBs — despite the higher per-circuit cost, the operational benefits of individual protection are significant.

VCB — Vacuum Circuit Breaker

When voltage exceeds 1,000 V, we enter the medium-voltage domain where fundamentally different circuit breaker technologies are required. The Vacuum Circuit Breaker (VCB) is the dominant technology for medium-voltage distribution at 1 kV to 40.5 kV.

How a VCB works

The VCB uses a vacuum interrupter — a sealed chamber at approximately 10⁻⁴ Pa — as the arc-extinguishing medium. When the contacts separate under fault conditions, a metal-vapor arc forms in the vacuum. Because there are virtually no gas molecules to sustain the arc, the metal vapor condenses on contact surfaces within microseconds of the current crossing zero. The vacuum recovers its full dielectric strength almost instantaneously — giving VCBs the fastest arc recovery of any medium-voltage switching technology.

Key VCB specifications

• Voltage: 1 kV to 40.5 kV (most common: 12 kV and 24 kV)
• Rated current: 400 A to 4,000 A
• Breaking capacity: 16 kA to 50 kA
• Mechanical life: 10,000 to 30,000 operations
• Maintenance: Sealed-for-life interrupter, no medium to replenish

NAIJI Electric manufactures a full range of VCBs including the ZW32-12 outdoor VCB, VN3-12E indoor VCB, and the flagship ZW32-12/T630-20G integrated VCB with built-in CT sensors and capacitor power supply for distribution automation. For a detailed comparison with SF6 breakers, see our VCB vs SF6 guide.

SF6 Circuit Breaker

SF6 circuit breakers use sulfur hexafluoride gas as both the insulating and arc-extinguishing medium. SF6 has a dielectric strength 2.5x that of air at atmospheric pressure, enabling very compact designs. At medium voltage (12-40.5 kV), SF6 breakers are used in gas-insulated switchgear (GIS) and ring main units (RMU). At high voltage (72.5-800 kV), SF6 remains the only commercially proven technology.

However, SF6 is the most potent greenhouse gas known — with a global warming potential (GWP) of 23,500 and an atmospheric lifetime of approximately 3,200 years. The EU F-Gas Regulation is phasing down SF6 in new medium-voltage equipment, and many utilities worldwide are transitioning to SF6-free alternatives at 12-24 kV. Vacuum technology is the primary replacement.

Other Specialized Circuit Breaker Types

AFDD — Arc Fault Detection Device

An AFDD detects dangerous series arc faults — arcing in loose connections, damaged cables, or deteriorating insulation that does not create an earth leakage (so RCCBs cannot detect it) and draws less current than the overload threshold (so MCBs cannot detect it). AFDDs use electronic pattern recognition to distinguish dangerous arcing from normal switching arcs. Required by IEC 60364 in sleeping areas, care homes, and wooden buildings in many jurisdictions.

MCB+DC — DC Circuit Breakers

Standard AC circuit breakers rely on the natural current zero crossing (every 10 ms at 50 Hz) to extinguish the arc. DC circuits have no zero crossing — the arc burns continuously. DC circuit breakers use longer arc chutes, magnetic blowout coils, and wider contact gaps to force-extinguish DC arcs. Critical for solar PV arrays (up to 1,500 V DC), battery storage systems, EV charging, and DC distribution in data centers.

Transfer Switches (ATS)

While not strictly circuit breakers, Automatic Transfer Switches combine two circuit breakers with interlocking logic to switch between primary and backup power sources (utility and generator). Key specifications include transfer time (typically 100-500 ms for emergency systems, <10 ms for critical loads requiring static transfer switches).

How Circuit Breakers Work Together: The Protection Hierarchy

In a complete power distribution system, different breaker types form a coordinated hierarchy from the utility supply down to the final socket outlet:

1. Medium-voltage incoming: VCB or SF6 breaker at 11/33 kV protects the utility connection and primary side of the transformer
2. Transformer secondary (main breaker): ACB at 800-4,000 A provides main protection with Category B selectivity
3. Sub-main feeders: MCCBs at 160-630 A protect risers and distribution boards
4. Final distribution: MCBs at 6-63 A protect individual circuits (lighting, sockets, equipment)
5. Personal protection: RCCBs or RCBOs at 30 mA sensitivity protect against electrocution

Each level must be selectively coordinated with the levels above and below it — so that only the breaker closest to the fault trips. For help designing this hierarchy, see our circuit breaker sizing guide.

Source Circuit Breakers Direct from the Manufacturer

NAIJI Electric manufactures circuit breakers across the voltage spectrum: from low-voltage switchgear assemblies with MCBs and MCCBs, through medium-voltage switchgear panels, to individual vacuum circuit breakers, SF6 circuit breakers, and auto-reclosers. We supply complete protection solutions — not just individual devices — ensuring coordination across every level of your distribution system.

Contact NAIJI Electric — circuit breaker and switchgear manufacturer since 2001, factory direct, ISO/CE/CCC certified, 30-60 day delivery.

Related guides: MCB vs MCCB | ACB vs MCCB | VCB vs SF6 | Circuit Breaker Sizing | IEC 60898 vs IEC 60947