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Circuit Breaker

By / December 19, 2019

Circuit Breaker 

Circuit breakers are automatic electrical switches designed to protect circuits from damage caused by overloads or short circuits. They instantly interrupt current flow when unsafe conditions are detected, serving as reusable alternatives to fuses in residential, commercial, and industrial applications.

Key Features:

✔ Current Ratings – 15A to 600A options
✔ Voltage Compatibility – 120V to 600V AC/DC
✔ Trip Curves – Type B (3-5x), C (5-10x), D (10-20x) for different loads
✔ Mounting Styles – DIN rail, panel mount, or bolt-on
✔ Safety Certifications – UL 489, IEC 60947-2
✔ Specialized Types – AFCI, GFCI, DC solar, and motor protection

Common Applications:

  • Home electrical panels

  • Industrial control cabinets

  • Solar PV systems

  • Data center power distribution

Circuit Breaker: The Essential Electrical Safety Device

What is a Circuit Breaker?

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current—typically resulting from an overload or short circuit. Its basic function is to interrupt current flow after protective relays detect a fault condition, unlike a fuse which operates once and must be replaced.

How Circuit Breakers Work

Operating Principle:

  1. Normal Operation: Current flows through contacts kept closed by a mechanical mechanism.

  2. Fault Detection: Built-in sensors detect excessive current (overload) or rapid current surge (short circuit).

  3. Tripping Mechanism: When a fault is detected, the mechanism releases, forcing contacts apart.

  4. Arc Suppression: Special chambers extinguish the electrical arc formed when contacts separate.

  5. Reset: After fault correction, the breaker can be manually reset (unlike fuses).

Key Components:

  • Contacts (fixed and moving)

  • Operating mechanism

  • Trip unit (thermal, magnetic, or electronic)

  • Arc extinguisher/chamber

  • Terminals

Types of Circuit Breakers

1. Based on Voltage Level:

Type Voltage Range Applications
Low Voltage (MCB/MCCB) < 1,000V Homes, commercial buildings, small industries
Medium Voltage 1kV – 72.5kV Distribution networks, industrial plants
High Voltage > 72.5kV Transmission lines, substations
Extra High Voltage > 245kV National grid transmission

2. Based on Interrupting Medium:

A. Air Circuit Breaker (ACB)

  • Uses atmospheric air as arc quenching medium

  • Types: Air Break, Air Blast

  • Applications: Low voltage distribution, industrial control panels

B. Oil Circuit Breaker

  • Uses insulating oil as arc quenching medium

  • Types: Bulk Oil, Minimum Oil

  • Applications: Mostly older substations (being phased out)

C. SF6 Circuit Breaker

  • Uses sulfur hexafluoride gas (excellent insulating properties)

  • Advantages: Compact, low maintenance, excellent performance

  • Applications: Medium to high voltage systems, GIS substations

D. Vacuum Circuit Breaker (VCB)

  • Operates in vacuum (10^-7 to 10^-5 torr)

  • Advantages: Noiseless, fire hazard-free, long life

  • Applications: Medium voltage, industrial plants, commercial buildings

3. Residential Breakers (Common in Homes):

Type Function Trip Characteristics
MCB (Miniature Circuit Breaker) Overload/short circuit protection B, C, D curves for different loads
RCCB/GFCI (Residual Current Device) Protection against earth leakage Trips at 30mA, 100mA, 300mA
RCBO Combined MCB + RCCB Complete protection in one device
AFCI (Arc Fault Circuit Interrupter) Detects dangerous arcs Prevents electrical fires

Technical Specifications & Selection

Key Parameters to Consider:

  1. Rated Current (In): Maximum continuous current (e.g., 15A, 20A, 50A)

  2. Breaking Capacity (Icu): Maximum short-circuit current it can interrupt

  3. Rated Voltage: System voltage it’s designed for

  4. Number of Poles: 1P, 2P, 3P, 4P

  5. Tripping Curve:

    • Type B: General purpose (3-5x In) – lighting, sockets

    • Type C: Motor circuits (5-10x In) – small motors, transformers

    • Type D: High inrush currents (10-20x In) – welding, X-ray machines

Selection Guide:

  • Lighting circuits: Type B MCB, 6-16A

  • Power sockets: Type B or C MCB, 16-32A

  • Kitchen appliances: Type C MCB, 20-32A + RCCB

  • AC units: Type C MCB, 20-40A

  • Main switch: 63-100A based on total load

  • Industrial motors: Type D MCCB or motor protection breaker

Installation & Safety Standards

Global Standards:

  • IEC 60898: MCBs for household and similar installations

  • IEC 60947: Low-voltage switchgear and controlgear

  • UL 489: Molded-case circuit breakers (North America)

  • NEC/NFPA 70: National Electrical Code (USA)

  • IET Wiring Regulations (BS 7671): UK standard

Installation Best Practices:

  1. Proper Sizing: Match breaker to wire size and load requirements

  2. Labeling: Clearly label all circuits in distribution board

  3. Accessibility: Install in accessible locations (not behind furniture)

  4. Environmental Conditions: Consider temperature derating

  5. Qualified Electricians: Always use licensed professionals for installation

For More Details Contact us on 0304-1111-988

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