Low voltage circuit breakers are categorized in multiple ways. I’ll introduce the common types, highlighting their structures, functions, and typical application scenarios to give you a comprehensive understanding.
- Miniature Circuit Breakers (MCBs)
- Structure and Operation: Miniature circuit breakers are compact in size. They usually have a simple toggle – type operating mechanism. Inside, there are bimetallic strips and electromagnetic tripping elements. The bimetallic strip bends when the current exceeds the rated value due to heat generated by the over – current, causing the breaker to trip. In case of a short – circuit, the electromagnetic element quickly activates and trips the breaker.
- Protection Functions: Primarily provide over – current and short – circuit protection. They are rated for relatively low currents, typically ranging from a few amperes to around 125 amperes.
- Applications: Widely used in residential electrical systems for protecting individual circuits such as lighting circuits, socket circuits in rooms. They are also used in small commercial and industrial applications for protecting small – scale electrical equipment and branch circuits.
- Molded Case Circuit Breakers (MCCBs)
- Structure and Operation: Molded case circuit breakers have a molded insulating case that encloses all the internal components. They have a more robust construction compared to MCBs. They can handle higher currents, usually from 16 amperes up to 2500 amperes or more. The internal structure includes advanced trip units, such as thermal – magnetic trip units for over – current and short – circuit protection, and some models may also have electronic trip units for more precise protection settings.
- Protection Functions: Offer over – current, short – circuit, and in some cases, earth leakage protection. They can be adjusted for different protection characteristics, such as long – time delay for overloads and instantaneous tripping for short – circuits.
- Applications: Commonly used in commercial and industrial low – voltage distribution systems. They are installed in switchboards, panelboards, and motor control centers to protect larger electrical loads like motors, transformers, and distribution circuits.
- Frame Circuit Breakers (also known as Air Circuit Breakers or ACBs)
- Structure and Operation: Frame circuit breakers are the largest and most powerful among low – voltage circuit breakers. They have a metal frame that provides mechanical support and protection for the internal components. They can handle extremely high currents, often ranging from 630 amperes to 6300 amperes or even higher. They use air as the arc – extinguishing medium. The operating mechanisms can be manual, electrical, or pneumatic. They have highly sophisticated trip units, including electronic trip units that can be programmed for various protection functions and settings.
- Protection Functions: Provide comprehensive protection against over – current, short – circuit, earth fault, and undervoltage. They can be set to have different tripping characteristics to coordinate with other protective devices in the electrical system.
- Applications: Used in large – scale industrial plants, power generation facilities, and high – rise building main distribution systems. They are installed as the main circuit breakers in switchgear and power distribution centers to protect critical electrical equipment and ensure the reliability of the overall power supply system.
- Residual Current Circuit Breakers (RCCBs) and Residual Current Circuit Breaker with Overcurrent protection (RCBOs)
- Structure and Operation: RCCBs are designed specifically to detect and respond to residual currents (leakage currents). They contain a sensitive current transformer that monitors the current flowing in the live and neutral conductors. When the difference in current between the two conductors (residual current) exceeds a preset value (usually 30 mA for personal protection), the breaker trips. RCBOs combine the functions of an RCCB and an MCB or MCCB, providing both residual current protection and over – current protection in a single device.
- Protection Functions: RCCBs protect against electric shock hazards by quickly disconnecting the circuit when a leakage current is detected. RCBOs offer additional protection against over – current and short – circuit, in addition to the leakage protection.
- Applications: Installed in residential, commercial, and industrial electrical systems, especially in areas where there is a high risk of electric shock, such as bathrooms, kitchens, outdoor electrical installations, and in circuits supplying portable electrical equipment.