Circuit Breakers Explained: Protection, Classification, and Usage
What is Circuit Breaker?
Circuit breakers are key protection devices used to automatically cut off faulty circuits in electrical systems. Their core functions include overload protection, short-circuit protection, and electrical isolation.
Circuit breakers are classified by application into Miniature (MCB), Molded Case (MCCB), Air (ACB), Vacuum (VCB), and Residual Current (RCCB/RCBO) types.
They operate via thermal (overload) and magnetic (short-circuit) tripping mechanisms for fast disconnection.
In motor control systems, breakers serve as main protection switches, working alongside contactors (for remote control) and thermal relays (for overload protection).
Selection should consider rated current, breaking capacity, pole count, and tripping curve (e.g., type C for standard motor protection) to match load and system needs accurately.
Main Components of the Circuit Breaker System
Din Rail Breaker
DIN rail circuit breakers are circuit breakers installed on DIN rails, commonly used in distribution boxes, with compact structure and easy installation. They are mostly used for electrical protection in homes and industries.
Poles: 1P, 2P, 3P, 4P
Rated Current (In): 6A - 125A
Breaking Capacity (Icn): 4.5kA - 25kA (per IEC/EN 60898)
Rated Voltage (Ue): 230V-400V AC (single/three-phase) | 24V-60V DC
Tripping Characteristic: Type C (general loads), Type D (high inrush loads), Type K (motor-specific)
Terminal Type: Screw clamp terminals / Spring-loaded terminals
Molded Case Circuit Breakers
Molded case circuit breakers are used for medium and high current protection (such as industrial power distribution). The shell is made of insulating material to prevent electric shock and arc flash. It is suitable for high-power equipment and main power protection.
Poles: 3P, 4P
Rated Current (In): 100A - 6300A
Breaking Capacity (Icu/Ics): 25kA - 200kA (IEC 60947-2)
Rated Voltage (Ue): 400V-690V AC (50/60Hz) | 250V-1000V DC
Tripping Characteristic: Thermal-Magnetic (Fixed) / Adjustable Electronic (LSI Protection)
Terminal Type: Front/Rear Cable Entry, Lug Terminals
Motor Protection Circuit Breakers
Motor protection circuit breakers are specially designed for motors to prevent overload, short circuit and phase loss. They are often used in control cabinets to directly protect motors.
Poles: 3P, 4P
Rated Current (In): 0.4A - 630A
Breaking Capacity (Icu/Ics): 10kA - 150kA (IEC 60947-2)
Rated Voltage (Ue): 400V-690V AC (50/60Hz) | 24V-250V DC
Protection Functions: Overload, Short-Circuit, Phase Loss, Phase Imbalance, Locked Rotor Protection
Tripping Adjustment: Thermal-Magnetic/Electronic
Control Voltage: 24V-240V AC/DC (Optional for Shunt Release/Undervoltage Release)
Terminal Type: Spring Clamp/Screw Terminal
Air Breaker
Air circuit breakers are used in high current situations (such as main switches in distribution rooms), and the arc extinguishing medium is air. They are suitable for high-power industrial equipment and busbar system protection.
Poles: 3P, 4P
Rated Current (In): 800A - 6300A
Breaking Capacity (Icu/Ics): 50kA - 200kA
Rated Voltage (Ue): 400V-690V AC (50/60Hz) | 250V-1500V DC
Protection Functions: Overload, Short-Circuit, Ground Fault, Arc Flash Detection
Tripping Unit: Microprocessor-Based (Adjustable L, S, G, I<sup>2</sup>t, Zone Selectivity)
Control Voltage: 24V-48V DC / 110V-440V AC (Integrated for Shunt/Undervoltage Release)
Terminal Type: Horizontal/Vertical Busbar Connection
DC Breaker
DC circuit breakers are used in DC circuits (such as solar systems, electric vehicles). They are designed differently from AC circuit breakers and are specifically designed to cut off DC current.
Poles: 1P (single pole), 2P (double pole)
Rated Current (In): 16A - 4000A
Rated Voltage (Ue): 60V-1500V DC (supports high voltage models of photovoltaic systems)
Breaking Capacity (Icu): 10kA-50kA (when voltage ≤500V DC) | 5kA-20kA (when voltage >500V DC)
Arc Extinguishing: Magnetic blow-out arc extinguishing design | Vacuum arc extinguishing
Tripping Characteristic: Fixed thermal magnetic tripping | Adjustable electronic tripping
Polarity Configuration: Single polarity/Bipolarity
Terminal Type: Screw terminal/Plug-in modular terminal
Smart Breaker
Circuit breakers with remote control, monitoring, power management and other functions. Commonly used in intelligent power distribution systems, which can control and monitor power consumption in real time through mobile phones or systems.
Number of poles (Poles): 1P, 2P, 3P, 4P
Rated current (In): 6A - 630A
Breaking capacity (Icu): 10kA - 100kA (supports AC/DC mixed breaking)
Rated voltage (Ue): 120V-400V AC (single/three-phase) | 48V-1000V DC
Communication protocol: Wi-Fi, Bluetooth, Zigbee, LoRaWAN, Modbus TCP, EtherCAT
Monitoring function: Real-time current/voltage/power monitoring, temperature sensing, energy metering (kWh, PF, THD)
Protection function: Overload, short circuit, leakage (30mA-3A adjustable), arc fault (AFCI), overvoltage/undervoltage, phase imbalance
Control mode: Local manual operation, APP remote control, automated scene linkage (IFTTT), API integration
Data recording: Event log (up to 1000), energy consumption history (statistics by day/month/year), fault waveform capture
Terminals: Spring clamp terminals/screw terminals