Most Popular Product – CNAISO MCB

1. Overview of MCB 

Miniature circuit breaker, referred to as MCB (Micro Circuit Breaker/ Miniature Circuit Breaker), is the most widely used terminal protection appliance in building electrical terminal power distribution devices. It is used for single-phase and three-phase short circuit, overload and overvoltage protection below 125A, including single-pole 1P, two-pole 2P, three-pole 3P, and four-pole 4P.

2. How MCB Work ?

Miniature circuit breakers are composed of operating mechanisms, contacts, protection devices (various releases), and arc extinguishing systems. Its main contacts are manually operated or electrically closed. After the main contact is closed, the free trip mechanism locks the main contact in the closed 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 power supply. When the circuit is short-circuited or severely overloaded, the armature of the overcurrent release is pulled in to make the free trip mechanism act, and the main contact disconnects the main circuit. When the circuit is overloaded, the thermal element of the thermal release will heat up and bend the bimetal, pushing the free release mechanism to act. When the circuit is undervoltage, the armature of the undervoltage release is released. Also actuate the free trip mechanism

3.Purpose of MCB ?

In civil building design, low-voltage circuit breakers are mainly used for line overload, short-circuit, over-current, voltage loss, under-voltage, grounding, leakage, automatic switching of dual power sources, and protection and operation of motors during infrequent starting. Principles In addition to complying with basic principles such as the use environment characteristics of low-voltage electrical equipment (see Industrial and Civil Power Distribution Design Manual), the following conditions should be considered:

1) The rated voltage of the circuit breaker should not be less than the rated voltage of the line;

2) The rated current of the circuit breaker and the rated current of the overcurrent release are not 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 line;

4) The selection of power distribution circuit breakers needs to consider the short-time delay short-circuit on-off capability and the coordination between delay protection levels;

5) The rated voltage of the undervoltage release of the circuit breaker is equal to the rated voltage of the line;

6) When used for motor protection, the selection of circuit breaker should consider the starting current of the motor and make it inactive within the starting time; see “Industrial and Civil Power Distribution Design Manual” for design calculations;

7) The selection of circuit breakers should also consider the selective coordination of circuit breakers and circuit breakers, circuit breakers and fuses.

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