How to choose a miniature circuit breaker

Posted by elcb on April 7th, 2018

When selecting a miniature circuit breaker, the following conditions should be considered:
1) The rated voltage of the circuit breaker shall not be less than the rated voltage of the line;
2) The rated current of the circuit breaker and the current rating of the overcurrent release shall not be less than the calculated current of the line;
3) The rated short-circuit breaking capacity of the circuit breaker is not less than the maximum short-circuit current in the circuit;
4) Selective distribution circuit breakers need to consider the short-delayed short-circuit breaking capacity and delay protection level coordination;
5) The rated voltage of circuit breaker undervoltage release is equal to the rated voltage of the circuit;
6) When used for motor protection, the selection of the circuit breaker must take into account the starting current of the motor and make it inactive during the starting time; design calculations refer to "Industrial and Civil Distribution Design Manual";
7) Select circuit breakers should also consider the selective cooperation of circuit breakers and circuit breakers, circuit breakers and fuses.
Circuit Breaker: A mechanical switching device that can turn on, load, and break the current under normal circuit conditions, and can also be turned on, carry a certain amount of time, and cut off current under specified abnormal circuit conditions.
Miniature circuit breaker working principle
Miniature circuit breakers consist of operating mechanisms, contacts, protection devices (various trip units), and arc extinguishing systems. Its main contacts are either manually operated or electrically closed. After the main contact is closed, the free tripping mechanism locks the main contact in the closing position. The coil of the overcurrent release and the thermal element of the thermal release are connected in series with the main circuit, and the coil of the undervoltage release is connected in parallel with the supply. When the circuit is short-circuited or severely overloaded, the armature of the over-current release pulls in, causing the free tripping mechanism to act, and the main contact opens the main circuit. When the circuit is overloaded, the thermal element of the thermal release heats up to bend the bimetal and push the free tripping mechanism. When the circuit is under voltage, the armature of the undervoltage release releases. The free trip mechanism is also actuated.

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