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What is MCB?

MCB is the abbreviation of Miniature Circuit Breaker, and some people call it Micro Circuit Breaker or small circuit breaker.

MCB is the most widely used terminal protection electrical appliance in the introduction of building electrical terminal power distribution devices. It is used for single-phase and three-phase short-circuit, overload, overvoltage protection under 125A, including single-pole 1P, two-pole 2P, three-pole 3P, and four-pole 4P.

Circuit shorts or overloads can occur due to a variety of reasons, such as incorrect connections or overcurrent conditions. MCB is similar to fuse. The only difference is that the fuse needs to be replaced after it is blown, while the MCB can be easily reset by clicking or pressing a button when it is overloaded.


What is DC MCB?

The thermal protection in the DC MCB prevents overload current, which is only slightly larger than the normal operating current. When a high fault current occurs, the magnetic protection will trip the DC MCB, and the response is always instantaneous.

DC MCB can be used to protect a single load that uses DC power, and it can also be used to protect main circuits such as inverters and photovoltaic battery packs.


What is AC MCB?

The power grid alternates at a frequency of 60 Hz or 60 cycles per second; hence the name “alternating current”. The voltage alternates between +V and -V, changing 60 times per second. This means that at a certain point the voltage is 0v, 60 times per second. The AC MCB will “disconnect” the connection at this 0v point, extinguish the arc, and protect the wiring from too much current.

There are many types of AC MCB on the market. However, the correct MCB should be selected according to the place used.


Characteristic curve

MCB usually works at a current below 100 amperes and is divided into type B (trip 3-5 times the rated current), type C (trip 5-10 times the rated current), and Type D (10-20 times the rated current) Tripping).

Type B MCB

This type of MCB is designed to trip at 3 to 5 times the rated current. These MCBs are usually used to switch small inductive or resistive loads with very small surges. Therefore, they are very suitable for residential and light commercial use.

Type C MCB

This type of MCB is designed to trip at 5 to 10 times the rated current. These MCBs are usually used to switch high-inductive loads with high surges, such as in fluorescent lamps and small motors. Therefore, they are suitable for industrial and high-inductance commercial facilities.

D type MCB

This type of MCB is designed to trip at 10 to 20 times the rated current. They are usually used for extremely high inductive loads with high inrush currents. Therefore, they are suitable for X-ray machines, UPS systems, large winding motors, and industrial welding equipment.

GEYA GYM9 AC MCB Characteristic curve


GEYA GYM9 DC MCB Characteristic curve



The difference between AC & DC MCB

The arc extinguishing point of DC MCB is higher.

In DC, the voltage is continuous and the arc is constant, which is more difficult to disconnect than AC MCB. The DC arc will not self-extinguish. This means they can only be extinguished by cooling or mechanical interruption. Therefore, DC MCBs must include other arc extinguishing measures: they usually have mechanisms to extend and dissipate the arc to simplify interruption.

In AC, arc interruption is relatively simple, because the current is alternating and its value is zero in each cycle that is easy to interrupt. The number of cycles per second of alternating current has been standardized in every country, and in most cases, it is 60 Hz or 50 Hz. Grids usually provide alternating current, while specialized industrial or battery-based applications tend to use direct current.

Please note!

Since the protection mechanisms of AC and DC are actually the same, some models of MCB are designed to be used under two currents. However, it is important to verify that the current types of the power supply and MCB are always the same. If the wrong type of MCB is installed, it will not be able to effectively provide protection, and electrical accidents may occur!

Another important consideration is that the wires connecting the DC MCB and the electrical equipment to be protected must have sufficient rated current. Even if the DC MCB is selected correctly, a cable that is too small will overheat, melt its insulation and cause electrical failure.

DC circuits can only use MCBs marked with DC ratings. Never try to use an AC MCB in a DC circuit! The arc cannot be extinguished, the wires will overheat and cause a fire. Don’t assume that AC MCBs can be used in DC circuits just because the ampere and volts match your needs. Conversely, do not use DC-rated MCB in AC circuits. Note: MCBs with dual AC and DC ratings can be used (this will be indicated on the manufacturer’s label). If both MCB and MCB meet the rated values, they will be clearly marked on the MCB, please check these values carefully.


The application of DC MCB

Both mcbs are not better than the other “mcb”, and each power source is suitable for different types of applications: AC is ideal for power generation, long-distance power transmission, and the operation of high-power electrical equipment; while DC power is dealing with batteries, Solar energy installations or precision machinery are more practical, while direct current is easier to control.

DC MCBs are commonly used in the following applications:

  1. Vehicle electrical components are found in both gasoline and electric vehicles. Every car has a fuse box with DC MCB.
  2. Uninterruptible power supply (UPS) systems usually use batteries. Even if the UPS supplies power to AC equipment, it must store energy in the battery pack in the form of DC power
  3. DC motor
  4. Certain types of arc welders
  5. High-efficiency LED lights
  6. Battery-powered circuits, such as battery-powered circuits in homes with solar panels installed in rural areas without power grids. Photovoltaic solar panels convert solar radiation into direct current, which can then be used to power electronic devices. It is very important to use DC MCB to protect solar panels because even a small photovoltaic installation costs thousands of dollars. When a household user has solar panels, he or she can choose to use both DC and AC electrical equipment. For example, homeowners with solar panels can purchase DC LED lights. In this case, DC MCB must be used for protection. The remaining DC power can be converted into AC power by an electric inverter. Homeowners with multiple DC circuits have installed separate fuse boxes for DC and AC power, each with multiple MCBs.
  7. Electric cars do not rely on fossil fuels at all but use high-capacity rechargeable batteries to work. These batteries are used in turn with charging piles specifically designed for electric vehicles. Since the system can work under direct current, DC MCB must be used. It is very common for photovoltaic solar panels to work with electric vehicle charging piles because the entire system works under direct current and does not need to be converted to alternating current to charge the electric vehicle. This system provides completely environmentally friendly and sustainable energy for transportation.


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