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How to choose low voltage circuit breaker correctly

Low-voltage circuit breakers have overload and short-circuit protection functions. According to their structure, they can be divided into frame circuit breakers (ACB), molded case circuit breakers (MCCB), and miniature circuit breakers (MCB). For MCB, the overload protection is realized by the inverse time limit characteristic composed of two metal plates with different thermal expansion coefficients combined into one metal plate. The larger the overload current, the shorter the action time, and the short circuit protection is Realized by electromagnetic release. Circuit breakers play a very important role in protecting the safety of lines and electrical equipment. So how to choose a low-voltage circuit breaker correctly, what factors need to be considered when choosing a low-voltage circuit breaker?
1. Choose the circuit breaker according to the use environment
1. For dusty environments, dust-proof circuit breakers should be used;
2. For environments with chemical corrosion, anti-corrosion circuit breakers should be used;
3. The altitude of the installation site exceeds 2000m, air cooling is required to be considered and the dielectric strength is reduced, and the circuit breaker used at high altitude should be selected;
4. For explosion and fire hazard locations, the requirements of the corresponding environment and specifications for circuit breakers should be met;
5. In high temperature (ambient temperature greater than 40 degrees Celsius), humid (relative humidity greater than 90%) places, you should choose anti-humidity products.


Choose according to normal working conditions
1. The rated frequency and rated voltage of the circuit breaker should be compatible with the nominal value of the circuit. In some cases, the maximum or minimum voltage that may occur in the loop under normal conditions is also considered.
The setting current of the circuit breaker is less than or equal to the allowable continuous ampacity of the conductor. It is to achieve protection of the circuit. If the setting value of the circuit breaker is greater than the allowable continuous ampacity of the conductor, during overload operation, the conductor may heat more than the maximum allowable during normal operation. Temperature, over time, will accelerate the aging of conductor insulation and deteriorate the insulation performance. When overvoltage occurs, insulation breakdown may occur, causing an electrical fire accident.


Choose according to short circuit conditions
1. The short circuit protection circuit breaker of the distribution line should cut off the power supply before the short circuit current causes heat and mechanical effects on the conductor and the connection;
2. The circuit breaker should be able to break the finite value of the expected short-circuit current periodic component at the installation site. The expected short-circuit current should be determined by calculation or measurement. When the sum of the rated current of the motor connected near the short-circuit point exceeds 1% of the short-circuit current. The effect of motor feedback current should be considered.

Knkong Electric

Date:2020-07-28 11:11

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