Author: Site Editor Publish Time: 2023-12-20 Origin: Site
The selection of circuit breakers should be based on specific usage conditions, choosing the category, rated working voltage, rated current, and setting current of the release, referencing the protection characteristic curves provided in product samples to select the protection characteristics. It's also necessary to verify the short-circuit characteristics and sensitivity coefficients.
Molded case circuit breakers, also known as device-type circuit breakers, have their grounding terminal, outer contacts, arc-extinguishing chamber, release, and operating mechanism enclosed within a plastic shell. Auxiliary contacts, undervoltage releases, and shunt releases often follow a modular design, making their structure highly compact. Typically, maintenance is not considered, suitable for branch circuit protection. Molded case circuit breakers usually include a thermal-magnetic tripping unit, and larger models may be equipped with solid-state tripping sensors.
The overcurrent release of molded case circuit breakers comes in two types: electromagnetic and electronic. Generally, electromagnetic molded case circuit breakers are non-selective and offer only long-delay and instantaneous protection modes. Electronic molded case circuit breakers offer long-delay, short-delay, instantaneous, and ground fault protection functions. Some newly introduced electronic molded case circuit breaker models also feature area-selective interlocking functionality.
They are commonly used for distribution feeder control and protection, as the main switch on the low-voltage side of small distribution transformers, terminal control for power distribution, and can also be used as power switches for various production machinery.
Miniature circuit breakers are the most widely used terminal protective devices in building electrical terminal distribution. They are used for single-phase and three-phase short-circuit, overload, overvoltage protection, and below 125A. These include single-pole 1P, 1P+N, two-pole 2P, three-pole 3P, 3P+N, and four-pole 4P models.
Their main contacts are operated manually or by motorized closing. Miniature circuit breakers consist of operating mechanisms, contacts, protective devices (various releases), and arc extinguishing systems. Their main contacts are operated manually or by motorized closing. After the main contacts close, the free-trip mechanism locks the main contacts in the closed position. The coil of the overcurrent release and the thermal element of the thermal release are in series with the main circuit, while the coil of the undervoltage release is in parallel with the power supply.
Protection and operation in non-frequent start-ups In civil building electrical design, miniature circuit breakers are primarily used for overload, short-circuit, overcurrent, undervoltage, low-voltage, grounding, leakage, dual power automatic switching, and for protection and operation in non-frequent motor start-ups, among other purposes.
