As the most representative enterprise in Wenzhou, YUANKY has a long history of development and a complete industrial chain. Our products are also very competitive in the market.such as MCB.

MCB (Miniature Circuit Breaker, small circuit breaker) is one of the most widely used terminal protection devices in low-voltage distribution systems. With advantages such as small size, convenient operation and precise protection, it is widely used in the distribution lines of industrial, commercial and civil buildings, undertaking core functions such as circuit overload and short-circuit protection. The following is a detailed analysis of its functional features from multiple aspects such as core functions, technical characteristics, and application features.

I. Core Protection Function: Ensure the safe operation of the circuit

The core value of MCB lies in the safety protection of distribution lines and electrical equipment. Its protection function is mainly achieved through precise action mechanisms, specifically including the following two types of core protection:

1. Overload protection function

When the circuit is operating normally, the current is within the rated range. However, when there are too many electrical devices or the circuit is overloaded for a long time, the current in the line will exceed the rated value, causing the wires to heat up. If overloaded for a long time, it may cause insulation aging, short circuits and even fires. The overload protection of the MCB is achieved through a bimetallic strip thermal trip device: when the current exceeds the rated value, the bimetallic strip bends and deforms due to the heat generated by the current, driving the trip mechanism to act, causing the circuit breaker contacts to open and cutting off the circuit.

Its overload protection has an inverse-time characteristic, that is, the greater the overload current, the shorter the action time. For instance, when the current is 1.3 times the rated current, the operating time may last for several hours. When the current reaches six times the rated current, the action time can be shortened to within a few seconds. This not only avoids unnecessary tripping caused by short-term minor overload but also quickly cuts off the circuit in case of severe overload, achieving flexible and reliable protection.

2. Short-circuit protection function

Short circuit is one of the most dangerous faults in circuits, usually caused by damage to the insulation of wires or internal faults of equipment. At this time, the current surges instantly (possibly reaching tens or even hundreds of times the rated current), and the huge electrical force and heat generated can instantly burn out wires and equipment, and even cause fires or electric shock accidents. The short-circuit protection of the MCB is achieved through an electromagnetic trip device: when the short-circuit current passes through the coil of the electromagnetic trip device, a strong electromagnetic force is generated, attracting the armature to strike the trip mechanism, causing the contacts to quickly open and cut off the circuit.

The action time of short-circuit protection is extremely short, usually within 0.1 seconds. It can quickly isolate the fault point before the fault expands, minimizing the damage of short-circuit faults to the line and equipment, and protecting personal and property safety.

Ii. Technical Features: Precise, stable and reliable

1. High precision in movement

The protection action values of MCB have been strictly designed and calibrated to ensure precise operation within the specified current range. The current setting value of its overload protection (such as not operating at 1.05 times the rated current and operating within the agreed time at 1.3 times the rated current) and the minimum operating current of short-circuit protection (usually 5 to 10 times the rated current) both comply with international standards (such as IEC 60898) and national standards (such as GB 10963). During the production process, each MCB must undergo strict calibration to ensure that the action time error under different current conditions is controlled within the allowable range, avoiding “failure to operate” (not tripping during faults) or “false operation” (tripping during normal operation).

2. Long mechanical and electrical life

MCB needs to frequently withstand closing and opening operations as well as fault current impacts, thus having strict requirements for mechanical and electrical life. Mechanical life refers to the number of times a circuit breaker operates in a no-current state. The mechanical life of high-quality MCB can reach over 10,000 times. Electrical life refers to the number of times it operates under load at the rated current, usually no less than 2,000 times. Its internal key components (such as contacts, tripping mechanisms, and springs) are made of high-strength materials (such as silver alloy contacts and phosphor bronze conductive parts), and through precise processing and heat treatment techniques, their wear resistance, corrosion resistance, and fatigue resistance are enhanced to ensure stable performance even after long-term use.

3. The breaking capacity is adapted to the scene requirements

Breaking capacity refers to the maximum short-circuit current value that an MCB can safely break under specified conditions, and it is the core indicator for measuring its short-circuit protection capability. Depending on the application scenarios, the breaking capability of MCB can be classified into multiple levels, such as:

In civilian scenarios, MCBS with breaking capabilities of 6kA or 10kA are commonly used, which can handle short-circuit faults in households or small commercial premises.

In industrial scenarios, MCBS with higher breaking capabilities (such as 15kA and 25kA) are required to adapt to environments with dense equipment and large short-circuit currents.

The realization of breaking capacity relies on an optimized arc extinguishing system (such as a grid arc extinguishing chamber). During short-circuit breaking, the arc is quickly introduced into the arc extinguishing chamber, and the arc is divided into multiple short arcs through metal grids, reducing the arc voltage and rapidly extinguishing the arc to prevent damage to the internal structure of the circuit breaker due to high arc temperatures.

Iii. Structural and Operational Characteristics: Miniaturization and convenience

Compact in size and easy to install

MCB adopts a modular design, is compact in size (typically with standard modules such as 18mm or 36mm in width), and can be directly installed on the rails of standard distribution boxes or distribution cabinets, saving installation space. Its compact structure enables independent protection of multiple circuits within a limited power distribution space. For instance, in a household distribution box, multiple MCBS can be used to control different circuits such as lighting, sockets, and air conditioners respectively, achieving separate protection and management, which is convenient for fault detection and power consumption control.

2. Easy to operate and simple to maintain

The operating mechanism of MCB is designed humanized. The closing (” ON “position) and opening (” OFF” position) operations are achieved through the handle. The status of the handle is clearly visible, allowing for intuitive judgment of the circuit’s on-off state. After a fault TRIP, the handle will automatically be in the middle position (” TRIP “position), facilitating users to quickly identify the faulty circuit. When resetting, simply move the handle to the “OFF” position and then push it to the “ON” position. No professional tools are required and the operation is simple. In daily maintenance, MCB does not require complex debugging or inspection. It only needs regular checks to ensure that the appearance is intact and the operation is smooth, resulting in low maintenance costs.

3. Excellent insulation performance

To ensure electrical safety, the casing and internal insulating components of the MCB are made of high-voltage and high-temperature resistant insulating materials (such as thermosetting plastics and flame-retardant ABS), with an insulation resistance of ≥100MΩ, capable of withstanding a 2500V AC voltage withstand test (no breakdown or flashover within 1 minute). It can still maintain good insulation performance in harsh environments such as dampness and dust, prevent leakage or phase-to-phase short circuits, and ensure the safety of operators and equipment.

Iv. Expanded Functions and Adaptability: Meeting Diverse Demands

1. Diversify derived types

In addition to the basic overload and short-circuit protection, MCB can also meet the needs of different scenarios through functional expansion. Common derivative types include:

- MCB with leakage protection (RCBO) : It integrates a leakage detection module on the basis of a regular MCB. When a leakage occurs in the circuit (residual current exceeds 30mA), it can quickly trip to prevent electric shock accidents and is widely used in household socket circuits.

- MCB with overvoltage/undervoltage protection: Automatically trips when the grid voltage is too high or too low to protect sensitive appliances such as refrigerators and air conditioners from damage caused by voltage fluctuations.

- Adjustable rated current MCB: Adjust the rated current value through a knob, suitable for scenarios where the load current needs to be flexibly adjusted.

2. Strong environmental adaptability

MCB can operate stably under a wide range of environmental conditions, typically applicable within a temperature range of -5℃ to 40℃ (special models can be extended to -25℃ to 70℃), with a relative humidity of ≤95% (no condensation), and can adapt to the climate conditions of different regions. Meanwhile, its internal structure has a certain ability to resist vibration and shock, and can operate reliably in industrial sites or transportation vehicles (such as ships and recreational vehicles) with slight vibration.

The differences from other circuit breakers:

MCB (Miniature Circuit Breaker): Mainly used for circuit protection with low current (usually less than 100 amperes).

MCCB (Molded Case Circuit Breaker): It is used for circuit protection with higher currents (typically greater than 100 amperes) and is suitable for large equipment and power distribution systems.

RCBO (Leakage Circuit Breaker): It combines overcurrent protection and leakage protection functions, and can simultaneously protect the circuit from overload, short circuit and leakage.