A circuit breaker is an automatically operated electrical switch that interrupts current flow when a fault is detected. Different types of circuit breakers, such as MCB, MCCB, and ACB, are designed for different current levels and applications. This guide explains how circuit breakers work, compares the main types, and helps you choose the right one for your installation.
What Is a Circuit Breaker?
A circuit breaker is a protective device that automatically opens a circuit when it detects an overcurrent, short circuit, or, in some designs, a residual current. Unlike a fuse, a circuit breaker can be reset after the fault is cleared, and it can also be used as a normal on/off switch for the circuit.
Circuit breakers are used at every level of an electrical installation, from the main incoming supply to the smallest branch circuit. They protect wiring, equipment, and people from damage caused by overloads, short circuits, and earth faults.
For B2B buyers, choosing the right circuit breaker matters because it directly affects safety, equipment protection, coordination with upstream and downstream devices, and total cost. An incorrectly selected breaker can nuisance-trip, fail to protect, or be damaged by a fault it was not designed to interrupt.
How Does a Circuit Breaker Work?
A circuit breaker monitors current through a thermal element (bimetallic strip) and a magnetic element (solenoid). Under normal conditions, current flows through the contacts without interruption. Under overload, the bimetallic strip heats up and bends, releasing a latch and opening the contacts. Under short circuit, the high current activates the magnetic trip instantly.
Once the contacts open, the arc is extinguished by arc chutes, gas, or vacuum depending on the breaker type. The breaker remains in the tripped state until it is manually or remotely reset.
Main Types of Circuit Breakers
MCB — Miniature Circuit Breaker
MCBs are the most common breakers in residential and light commercial installations. They are modular, DIN-rail mounted, and rated for currents typically from 1 A to 125 A at 230/400 V.
Features: Compact, modular, easy to replace, fixed trip curve. Typical use: Branch circuit protection in homes, offices, and small distribution boards. Best for: Final circuit protection.
MCCB — Molded Case Circuit Breaker
MCCBs are larger breakers housed in a molded case, rated from 10 A to 1600 A at 400 V or 690 V. They offer adjustable trip settings and higher breaking capacities than MCBs.
Features: Higher current, adjustable trip, higher breaking capacity. Typical use: Main incoming breaker, large motor protection, distribution feeders. Best for: Industrial and large commercial installations.
ACB — Air Circuit Breaker
ACBs are large, open-frame breakers rated from 630 A to 6300 A at 400 V to 690 V. They are used as main incoming breakers in large switchboards and offer electronic trip units, communication, and full withdrawability.
Features: Very high current, electronic trip, withdrawable option, communication ready. Typical use: Main incoming breaker in large substations and data centers. Best for: Critical high-current applications.
VCB — Vacuum Circuit Breaker
VCBs use a vacuum interrupter to extinguish the arc and are common in medium-voltage switchgear at 3.6 kV to 40.5 kV. They are not part of the MCB/MCCB/ACB family but are often compared for completeness.
Features: Long life, low maintenance, environmentally friendly compared with SF6. Typical use: Medium-voltage power distribution, motor feeders, transformer switching.
Comparison of MCB, MCCB and ACB
| Feature | MCB | MCCB | ACB |
|---|---|---|---|
| Current range | 1 – 125 A | 10 – 1600 A | 630 – 6300 A |
| Voltage | Up to 400 V | Up to 690 V | Up to 690 V |
| Breaking capacity (Icu) | Up to 25 kA | Up to 100 kA | Up to 150 kA |
| Trip unit | Thermal-magnetic (fixed) | Thermal-magnetic or electronic (adjustable) | Electronic (adjustable) |
| Mounting | DIN rail | Panel or DIN adapter | Withdrawable or fixed |
| Communication | No | Optional | Standard (Modbus, etc.) |
| Cost | Low | Medium | High |
| Typical use | Branch circuits | Feeders, motors | Main incoming |
Key Specifications to Compare
- Rated current (In) — Maximum continuous current the breaker can carry.
- Rated voltage (Ue) — Maximum operating voltage.
- Breaking capacity (Icu) — Maximum short-circuit current the breaker can interrupt.
- Service breaking capacity (Ics) — Breaking capacity after which the breaker can still operate normally; usually 50%, 75%, or 100% of Icu.
- Trip curve — B, C, D, K, or Z for different load types.
- Number of poles — 1P, 2P, 3P, or 4P.
- Standard — IEC 60898 (MCB), IEC 60947-2 (MCCB/ACB), or local equivalent.
Requirements may vary by application, market, and applicable standard. Confirm the relevant specification with your engineer or supplier before ordering.
How to Choose the Right Circuit Breaker
- Load type and current — Match In to the design load with margin.
- Trip curve — Select B for resistive loads, C for general motors, D for heavy inrush.
- Short-circuit level — Icu must exceed the available fault current at the installation point.
- Coordination — Ensure upstream and downstream breakers are coordinated (selectivity and back-up).
- Installation — DIN rail, panel, or withdrawable.
- Monitoring — Electronic trip and communication for critical feeders.
- Standard — Local or international standards.
- Spare parts — Availability of spare breakers and trip units.
Trip Curves Explained
Trip curves describe how quickly a breaker trips at a given multiple of its rated current. Common curves include:
- B curve — Trips at 3 to 5 In. Used for resistive loads such as heating and lighting.
- C curve — Trips at 5 to 10 In. Used for general motors and small transformers.
- D curve — Trips at 10 to 20 In. Used for heavy motors, transformers with high inrush, and X-ray equipment.
- K curve — Trips at 8 to 12 In. Common for motor protection with high inrush.
- Z curve — Trips at 2 to 3 In. Used for sensitive electronic loads.
How to Inspect Circuit Breaker Quality
- Marking and certification — Verify IEC or local standard mark and breaking capacity.
- Mechanical operation — Manual close and open several times; check smoothness.
- Thermal trip — Apply overload current and verify trip time against curve.
- Magnetic trip — Apply short-circuit current and verify instantaneous trip.
- Insulation — Hi-pot test between poles and to ground.
- Terminal integrity — Check terminal screws and tightening torque.
- Accessories — Verify auxiliary contacts, shunt trip, and under-voltage release if fitted.
What Information Should Be Included in an RFQ?
- Type — MCB, MCCB, ACB, or VCB.
- Rated current, poles, and voltage.
- Breaking capacity (Icu) and service breaking capacity (Ics).
- Trip curve and trip unit type.
- Mounting method and accessories.
- Standard compliance.
- Quantity, packaging, and destination port.
How to Choose a Reliable Circuit Breaker Supplier
- Type testing — IEC 60898, IEC 60947-2, or local equivalent test reports.
- Standard compliance — Third-party certification marks.
- Trip unit options — Wide range of trip units and accessories.
- Coordination tables — Selectivity and back-up data with other devices.
- Spare parts — Spare breakers, trip units, and accessories.
- Export experience — Documentation and packaging for international shipping.
Frequently Asked Questions
What is the difference between MCB and MCCB?
MCBs are smaller, modular breakers for branch circuits up to 125 A. MCCBs are larger molded-case breakers for currents up to 1600 A, with adjustable trip and higher breaking capacity.
Can I use an MCB instead of an MCCB?
Only if the current, voltage, and short-circuit level of the circuit are within the MCB rating. MCCBs are required for higher currents and fault levels.
What does Icu and Ics mean?
Icu is the ultimate breaking capacity, the maximum fault current the breaker can interrupt. Ics is the service breaking capacity, after which the breaker can still operate normally. Ics is always equal to or lower than Icu.
How do I select the trip curve?
Use B for resistive loads, C for general motors and small transformers, and D for heavy motors and equipment with high inrush current.
What is selectivity in circuit protection?
Selectivity means that, during a fault, only the breaker closest to the fault trips, while upstream breakers remain closed. Proper selectivity avoids widespread outages.
How often should circuit breakers be tested?
Thermal-magnetic breakers should be exercised and tested at least once a year. Electronic trip units should be tested and re-calibrated per the manufacturer’s schedule, typically every 3 to 5 years.
Are circuit breakers reusable after a short-circuit trip?
Yes, if the fault current was within the breaker’s Ics. After an Icu-level trip, the breaker may be damaged and should be inspected or replaced.
Source Circuit Breakers from BANGE Electric
BANGE Electric provides integrated electrical distribution and cable system solutions, including MCB, MCCB, and ACB, alongside busway, distribution boxes, switchgear, and cable trays. We support specification customization, consistent quality control, export packaging, and reliable international supply.
To receive a quotation, send us your breaker type, rated current, breaking capacity, trip curve, and destination port.