Circuit breaker

BreakerSymbols

AEG Circuit breaker type ME 800 (1)

Four 1 pole circuit breakers fitted in a meter box

Standard Trip Characteristic of a Thermomagnetic Circuit Breaker

LargeCircuitBreaker

Circuitbreaker

Circuit breaker

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overcurrent or short circuiting. Its basic function is to interrupt current flow after a fault is detected. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.

Operation

Circuit breakers are made in varying sizes, from small devices that protect low-current circuits or individual household appliances, to large switchgear designed to protect high voltage circuits feeding an entire city. The generic function of a circuit breaker, regardless of type, is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow.

Types of Circuit Breakers

Circuit breakers can be classified into several types based on their features and applications:

• Miniature Circuit Breaker (MCB): Used for low voltage applications, typically in residential and commercial buildings.
• Molded Case Circuit Breaker (MCCB): Used for higher current ratings and can be found in industrial applications.
• Air Circuit Breaker (ACB): Used for high voltage applications and can interrupt large currents.
• Vacuum Circuit Breaker (VCB): Utilizes a vacuum to extinguish the arc when the circuit is broken.
• SF6 Circuit Breaker: Uses sulfur hexafluoride gas to quench the arc and is used in high voltage applications.

Components

A typical circuit breaker consists of the following components:

• Contacts: Allow current to flow when closed and interrupt the flow when open.
• Arc Extinguishers: Devices that extinguish the arc formed when the contacts open.
• Operating Mechanism: Provides the means to open and close the contacts.
• Trip Unit: Senses the fault condition and initiates the operation of the operating mechanism.

Applications

Circuit breakers are used in various applications, including:

• Residential wiring
• Commercial buildings
• Industrial plants
• Power distribution networks
• Automotive electrical systems

Maintenance

Regular maintenance of circuit breakers is essential to ensure their reliable operation. This includes:

• Visual inspection for signs of wear or damage.
• Testing the trip unit to ensure it operates correctly.
• Cleaning and lubricating moving parts.
• Checking and tightening electrical connections.

Related Pages

• Fuse (electrical)
• Electrical wiring
• Power distribution
• Electrical engineering
• Short circuit
• Overcurrent

See Also

• Switchgear
• Relay
• Electrical safety

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