How to choose A, B, C, OR D miniature circuit breakers MCB

There are four universal trip characteristics of miniature circuit breakers: A, B, C, and D. So how do we choose?


(1) TYPE A circuit breaker: 2 times the rated current, rarely used, generally used for semiconductor protection (generally use fuse); The so-called number of times the current, is the impact current, withstand a certain duration of the switch does not trip, its characteristics is to avoid the impact current.

Selection of tripping device of low-voltage circuit breaker: tripping device type of circuit breaker has over-current tripping device, under-voltage tripping device, shunt tripping device, etc. Overcurrent tripping device can also be divided into overload tripping device and short-circuit current tripping device, and has long delay, short delay, instantaneous points, overcurrent tripping device is the most commonly used.The action current setting value of overcurrent tripping device can be fixed or adjustable, usually by rotating or adjusting lever. Electromagnetic overcurrent tripping device has the same fixed and adjustable two. The electronic overcurrent tripping device is generally adjustable.

The breaking capacity of a circuit breaker refers to the ability to withstand the maximum short-circuit current, so the breaking capacity of a rotary circuit breaker must be greater than the short-circuit current of its protection equipment.Overcurrent trip according to the installation and can be divided into fixed installation or module, fixed for the installation of the factory trip and circuit breaker is processed into an organic whole, once after they leave the rated current of the trip is adjustable, and modular installation trip as a circuit breaker installed modules, can be adjustable, flexibility is strong.

Instantaneous type: 0.02s, for short circuit protection;

Short delay type: 0.1-0.4s, used for short circuit, overload protection;

Long delay: less than 10S, used for overload protection;

Currently commonly used DZ series air switch (small circuit breaker with leakage protection), common specifications are: C16, C25, C32, C40, C60, C80, C100, among them C represents to take off current characteristic is C, namely jump current, for example C20 expresses jump current is 20A, trip characteristic is C curve, install 3500W water heater to want to choose the circuit breaker of C20 commonly, install 6500W water heater to want to use the circuit breaker of C32.

Circuit breaker is used to protect the wire and prevent fire, so according to the size of the wire to choose rather than according to the power of the electrical selection. If the circuit breaker is too large, it will not protect the wire. When the wire is overloaded, the circuit breaker will still not jump, which will bring hidden dangers to the home safety.

1.5 square wire with C10 switch

2.5 square wire with C16 or 20 switch

4 square wire with C25 switch

6 square wire with C32 switch

For air switches used for motors with load, type D characteristics should be selected to avoid the high starting current of motor starting which is 5-8 times higher.

(2) B  type circuit breaker: 2-3 times the rated current, generally used for pure resistive load and low-voltage lighting circuit, often used for household distribution box, to protect household appliances and personal safety, less use at present.

(3) C type circuit breaker: 5-10 times the rated current, need to be in 0.1 seconds off, the characteristics of the circuit breaker is the most commonly used, often used to protect distribution lines and lighting lines with higher switching current.

(4) D type circuit breaker: 10-20 times the rated current, mainly in the use of electrical instantaneous current larger environment, the general family is less used, suitable for high sense of load and large impact current system, often used to protect equipment with a high impact current.

Post time: Nov-17-2021