When it comes to miniature circuit breakers, I’m sure most electricians are no strangers. But if we talk about the choice of Type-A, B, C, D miniature circuit breakers, may be a lot of electrical personnel are half-knowledge.
We all know that the miniature circuit breaker (MCB, Miniature Circuit Breaker) is a widely used in the electrical system of circuit protection equipment, mainly used to prevent damage to the circuit due to overload or short-circuit, can provide protection for the building electrical terminal power distribution devices.
It is suitable for AC 50/60Hz rated voltage 230/400V, rated current up to 63A line overload and short-circuit protection, but also under normal circumstances as a line of infrequent operation of the switching purpose. Miniature circuit breakers (small circuit breakers) are mainly used in various places such as industrial, commercial, high-rise and civil residences.
There are different types of miniature circuit breakers according to their action characteristics and applications, of which type-A, B, C and D are the most common ones. Each type of miniature circuit breaker has its unique characteristics and application scenarios, and understanding these differences is crucial to choosing the right miniature circuit breaker.
This article will detail the differences between type-A, B, C, and D miniature circuit breakers, as well as their respective application scenarios.
A-type Miniature Circuit Breaker
Characteristics:
A-type miniature circuit breakers are usually characterized by finer overload protection with shorter trigger times. Its action curve is designed for very low overload currents and is suitable for circuits that are more sensitive to changes in current.
Applications:
A-type miniature circuit breaker is mainly used in DC circuits, especially in electronic equipment and battery chargers that require high current fluctuation. It is also suitable for electrical systems with weak power, such as the protection of low-power appliances.
B-type miniature circuit breaker
Characteristics:
B-type miniature circuit breaker has lower overload protection action characteristics. Normally, when the current reaches 3 to 5 times the rated current, B-type Miniature Circuit Breaker will trip quickly.
Applications:
B-type miniature circuit breaker is generally used for purely resistive loads and low-voltage lighting circuits, commonly used in household distribution boxes to protect household appliances and personal safety, and is less used at present.
C-type miniature circuit breaker
Characteristics:
C-type miniature circuit breakers are suitable for medium-capacity loads, and their overload protection trigger current is usually 5 to 10 times the rated current. This type of miniature circuit breaker has a wide range of applications, especially in the case of equipment with high starting currents.
Applications:
C-type miniature circuit breakers are widely used where protection is required for motors, transformers and other electrical equipment with high starting currents. They are commonly used in industrial applications such as air conditioning equipment, elevators, pumps, etc., as well as in some factory electrical systems.
D-type miniature circuit breaker
Characteristics:
D-type miniature circuit breakers have the highest overload protection trigger current, usually 10 to 20 times the rated current. This type of circuit breaker is suitable for equipment with very high starting currents, such as large motors or industrial machinery.
Applications:
D-type miniature circuit breakers are mainly used to protect heavy electrical equipment, such as industrial pumps, cranes, compressors and other equipment, which generate high currents for a short period of time during startup and therefore require a D-type circuit breaker to provide effective protection. Generally less used in household.
Currently commonly used DZ47 series of small circuit breakers have the following specifications:
C1, C2, C3, C4, C6, C10, C16, C25, C32, C40, C60, C80, C100, C125A, etc., where C stands for the trip current characteristics of C, that is, trip current, such as C20 on behalf of the trip current of 20A, the trip characteristics of the curve of the C. 3500W water heater installation is generally used C20 circuit breaker, 6500W water heater installation General use of C32 circuit breaker.
Is C-type circuit breaker suitable for motor circuit?
As we all know, ordinary lighting circuits are usually protected by C-type MCB; motor circuits are usually protected by D-type MCB, but can C-type MCB be used for motor circuits?
First, let’s compare the differences between C-type and D-type circuit breakers:
C-type MCB: with overload protection and short-circuit protection, short-circuit protection tripping value is 5-10 times of the rated current;
D-type MCB: with overload protection and short-circuit protection, short-circuit protection tripping value of 10-20 times the rated current;
The overload protection function of both products is the same, and the difference only lies in the tripping range of short-circuit protection.
In the motor circuit, the general load no starting current, that is, the starting current is the rated current; but the three-phase motor starting current is about 6-8 times the rated current.
For example: 4kW three-phase motor, the rated current is 9A, but the starting current is calculated as 10 times the rated current, i.e. 90A.
When selecting the type, we usually choose D-type 16A micro-break as the protection device of this motor. Calculated by 10 times the action current, the short-circuit protection action current is 160A, which can avoid the motor starting current.
If we choose C type 16A micro-breaker as the protection device, according to the action current of 5 times calculation: the short-circuit protection action current is 80A, which can’t avoid the starting current of the motor.
Does it mean that C type circuit breaker can never be chosen?
Of course not. Technically, if C type 25A micro circuit breaker is chosen as the protection device, the action current of short circuit protection is calculated by 5 times of the action current, i.e., if C type 125A is chosen, the starting current of the motor can be avoided.
So, how to choose the right miniature circuit breaker?
Choosing the right miniature circuit breaker depends on the type of load, the amount of current and the starting characteristics of the appliance. Here are a few key factors to consider when making your selection:
Current capacity: When choosing a miniature circuit breaker, make sure its current rating meets the requirements of the appliance it is protecting. A current rating that is too small may result in frequent tripping of the breaker, while a current rating that is too large may not effectively protect the circuit.
Overload Characteristics: As mentioned earlier, different types of miniature circuit breakers have different overload protection characteristics. For equipment with high starting currents, it is more appropriate to choose C-type or D circuit breakers, while for general household appliances, B-type circuit breakers are more suitable.
Application environment: When choosing miniature circuit breakers, the specificity of the environment in which they are used should also be taken into account. For example, if it is used in industrial environments, you may need to choose to carry more current circuit breaker, while the family electricity is usually a simpler choice of B-type circuit breakers can be.
Code requirements: Different countries and regions have different codes and standards for electrical protection equipment. When choosing a miniature circuit breaker, you need to make sure that it complies with local safety standards and electrical codes.
Generally speaking, the principle of selecting circuit breakers is: the rated current of the circuit breaker needs to be greater than the load current, and then according to the nature of the load to choose to use C-type or D-type.
Although D-type circuit breakers are designed for motor loads, this does not mean that C-type circuit breakers cannot be used. In some cases, it is enough to adjust the calculation method and choose flexibly.
We should make a reasonable choice according to the specific application requirements and economic factors.
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