The miniature circuit breaker is mainly used for overload and short circuit protection in the line with rated voltage of 400V and below and rated current of 125A, as well as infrequent operation of motor and infrequent conversion of line.
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Miniature circuit breakers are widely used in industry, commerce, high-rise buildings and residential buildings because of their track installation, modular size, diversified functions, artistic modeling and safe use.
Nader various types of miniature circuit breakers
Main parameters of miniature circuit breaker
1. Rated voltage, the voltage value of miniature circuit breaker when working, and the rated voltage of miniature circuit breaker shall not be lower than that of circuit.
2. Rated current, the rated current of the miniature circuit breaker refers to the maximum current that the miniature circuit breaker can work normally for a long time. If the load current exceeds this value, the thermal trip element will heat up, bend the bimetallic sheet and push the free tripping mechanism to trip.
3. Shell rating current, which refers to the rated current of the maximum release installed in the frame or plastic shell with basically the same or similar geometric dimensions. The shell rating current and the rated current of the circuit breaker are different concepts. If the frame current is the same, the size of the products produced by the same factory is exactly the same. However, if the rated current of two circuit breaker releases is the same and the rated current of shell frame is different, their sizes will be very different.
4. Rated breaking capacity and ultimate breaking capacity.
(1) The rated limit short-circuit breaking capacity refers to the limit point of action caused by the maximum short-circuit current that the protection device can bear. The miniature circuit breaker with limit breaking can not be reused.
(2) The rated operation short-circuit breaking capacity refers to the ability of the protection device to act due to the short-circuit current it can bear in the normal operation process. It can be reused.
5. According to the tripping characteristics of circuit breakers, miniature circuit breakers are divided into B, C, D, etc., and their meanings are as follows:
Type B tripping characteristic: the tripping current is (3 ~ 5) In, which is suitable for household distribution system, household appliances protection and personal safety protection.
Type C tripping characteristic: the tripping current is (5-10) In, which is suitable for protecting distribution lines, lighting lines and motor circuits with high connecting current.
Type D tripping characteristic: the tripping current is (10 ~ 20) In, which is suitable for protecting equipment with high impulse current, such as transformer, solenoid valve, etc.
NDB1-63 Series Trip Curve Chart
Selection rules of miniature circuit breaker
General selection rules
1. The rated working voltage of miniature circuit breaker is greater than or equal to the rated voltage of line.
2. The rated current of miniature circuit breaker is greater than or equal to the calculated load current of the line.
3. The rated short-circuit breaking capacity of miniature circuit breaker is greater than or equal to the maximum short-circuit current that may occur in the line.
4. The setting current of instantaneous release of miniature circuit breaker is less than 0.8 times of single phase ground short circuit current at the end of line.
5. Considering the short-time delay short-circuit making and breaking capacity and the coordination between delay protection stages.
6. Determine the pole number of miniature circuit breaker according to the number of lines to be protected. For example, the general household electricity is single-phase, and the line is composed of a zero line and a live line. If both lines need protection, the circuit breaker with two poles is selected; if the zero line is not required to be protected, the one pole circuit breaker is selected.
NDB1-125 Series
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NDB1-125 Series wiring diagram
7. Determine the amperage of the miniature circuit breaker according to the load of the line. For example, if the carrying capacity of the line is 20A and the rated working current of the electric appliance is 10A, the selection of circuit breaker should be > 10A and < 20A.
8. The instantaneous protection type is determined according to the resistance type of the electric appliance in the circuit. There are three types of instantaneous protection, and the corresponding current protection multiples are B: 3 ~ 5In, C: 5 ~ 10In, D10 ~ 14In (in is the rated current). If it is only incandescent lamp, type B can be selected, type C can be selected for general power consumption, and type D can be selected for air conditioning protection.
Selection of small circuit breaker for conductor protection
The setting value of long delay current is less than the line load current.
The setting value of instantaneous action is less than (6-20) times of line calculated load current.
Selection of small circuit breaker for motor protection
Setting value of long delay current = rated current of motor.
Setting value of instantaneous action = (8-15) times of rated current of motor (for protective squirrel cage motor); setting value of instantaneous action = (3-6) times of rated current of motor (for protected wound motor).
Selection of suitable miniature circuit breakers by on-line tools
On Quisure.com, you can quickly and accurately select the required miniature circuit breaker model through parameters and purchase it.
Choose the right miniature circuit breaker at Quisure
The Ultimate MCB buying guide to help you make the right choice
MCBs, which are modern alternatives to fuses, play a crucial role in the safety and efficiency of your electrical systems. They are responsible for automatically breaking the circuit during overload and short circuit conditions, thereby preventing wire damage and fire hazards.
MCBs come in a variety of types, each designed for specific applications and offering different levels of protection. However, selecting the most suitable MCB for your project can be challenging, given the variety of types available on the market. This blog will serve as an ultimate guide to help you choose an MCB that perfectly meets your needs.
MCB Selection Guide
To select the right MCB, it&#;s important to understand key MCB specifications:
- Current Rating: This indicates the maximum current that an MCB can handle without tripping. If it&#;s rated for a current lower than required, it will trip too frequently, leading to unnecessary power interruptions. Conversely, if the MCB is rated for a higher current than necessary, it won&#;t provide adequate protection in the event of a short circuit or overcurrent situation. Typically, MCBs are rated for currents of up to 125A.
- Tripping Curve: MCBs come with different tripping curves &#; B, C, and D, indicating the breaker&#;s sensitivity to instantaneous overcurrent.
- B-Curve: Ideal for residential or light commercial applications like heaters and lamps. Trips between 3 to 5 times the rated current.
- C-Curve: Suited for commercial and industrial applications with moderate surges. Trips between 5 to 10 times the rated current.
- D-Curve: Best for circuits with high inrush currents like motors and transformers. Trips between 10 to 20 times the rated current.
- Breaking Capacity: The breaking capacity of an MCB is the maximum fault current it can safely interrupt without sustaining damage. Understanding this capacity is crucial as it determines the device&#;s suitability for specific installations. The breaking capacity of an MCB is typically expressed in kiloamperes (kA). For instance, a 10kA miniature circuit breaker is designed to safely interrupt currents up to 10,000 amperes. This capacity should exceed the maximum expected current in the circuit it protects. Common capacities include 6kA, 10kA, and 15kA.
- MCB Pole Types: The number of poles in an MCB indicates the count of live wires the device can protect. The most commonly used types are 1-pole, 2-pole, 3-pole, and 4-pole.
A 1-pole or single-pole MCB, typically utilized in residential settings, protects a single live wire. The 2-pole MCB, often found in commercial and industrial settings, safeguards two live wires. Although less common, the 3-pole MCB is used for three wires and is mainly seen in industrial applications. Lastly, the 4-pole MCB, which protects four live wires, is sometimes employed in extensive commercial and industrial applications.
- MCB Voltage Rating: This parameter defines the operating voltage range of an MCB, specifying the highest voltage at which the device can operate safely. Residential MCBs commonly have voltage ratings of either 240 volts (V) or 415 V. MCBs rated at 240 V are suitable for single-phase electrical systems, commonly found in household environments. Conversely, MCBs with a 415 V rating are intended for three-phase systems, typical in commercial and industrial settings. It&#;s essential that the MCB&#;s voltage rating is equal to or exceeds the nominal voltage of the circuit it is protecting.
The Ultimate MCB Selection Chart
The selection chart below categorizes MCBs based on application, current rating, tripping curve, and breaking capacity.
Application Area
Current Rating
Tripping Curve
Breaking Capacity
Residential (Lighting and Outlets)
6A, 10A, 16A
B-Curve
6kA
Residential (Heavy Appliances)
20A, 25A
B-Curve
6kA
Commercial (General Use)
16A, 20A, 25A
C-Curve
10kA
Commercial (Heavy Machinery)
32A, 40A
C-Curve
10kA
Industrial (Motors, Transformers)
40A, 50A, 63A
D-Curve
15kA
Specialized Equipment
As per requirement
B, C, or D Curve
6kA, 10kA, or 15kA
Multiple factors need to be considered in MCB Selection. It should start with calculating the total load of the circuit to determine the appropriate current rating. Then, consider the nature of the load (resistive, inductive, motor-based) to select the right tripping curve. In areas prone to surges or spikes, opt for MCBs with higher breaking capacities.
Conclusion:
Choosing the right MCB is vital for protecting electrical circuits from damage and ensuring safety. By using the ultimate MCB selection chart and considering factors like load, type of load, etc., you can select the most suitable MCB for your needs. Remember, while MCBs play a critical role in circuit protection, proper installation, and regular maintenance are equally important for sustained electrical safety.
Frequently Asked Questions (FAQs) :
Q1. What is the primary function of an MCB?
The primary function of MCB is to protect electrical circuits from damage caused due to current overload or short circuits. It automatically cuts off the electrical supply when excessive current is detected, thereby preventing damage to the circuit and ensuring safety.
Q2. How do I determine the right current rating for my MCB?
To determine the right current rating for your MCB, you should calculate the total current draw of the devices on the circuit and then select an MCB with a rating slightly higher than this total to ensure safety and prevent frequent tripping.
Q3. Can I replace an MCB on my own?
Replacing an MCB can be done on your own if you have basic electrical knowledge and the right tools. However, it&#;s crucial to ensure that the main power is off and to follow safety procedures. If you&#;re unsure, it&#;s always safer to consult a professional electrician.
Q4. Are all MCBs compatible with solar power systems?
Not all MCBs are compatible with solar power systems. Solar-specific MCBs are designed to handle the unique characteristics of solar panel outputs, such as higher DC voltages and current, and are necessary for safe and efficient solar system operation.
Q5. What is the breaking capacity of an MCB?
The breaking capacity of an MCB, also known as interrupting capacity, is the maximum current it can safely interrupt without getting damaged. This value, typically measured in Amperes (A), indicates the highest level of fault current that the MCB can effectively break in the event of a short circuit or overload.
Q6. Is it safe to buy MCB online?
Yes, it is generally safe to buy MCBs online, provided you purchase from reputable and certified retailers or manufacturers. Ensure that the MCBs are of the correct specifications for your needs and meet safety standards.
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