AC MCB VS DC MCB: What Their Difference

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

Miniature circuit breakers are the most widely used terminal protection appliances in building electrical terminal power distribution devices. It is used for single-phase, three-phase short circuit, overload, and overvoltage protection below 125A, including single pole 1P, bipolar 2P, three pole 3P, and four pole 4P.

Due to various reasons, such as incorrect connection or over-current conditions, a short circuit or overload may occur in the circuit. MCB is similar to a fuse. The only difference is that the fuse needs to be replaced after it is blown, while the miniature circuit breaker can be easily reset by clicking or pressing a button when overloaded.

1. What is DC MCB?

The thermal protection of the DC miniature circuit breaker can prevent overload current, which is only slightly larger than the normal operating current. DC miniature circuit breakers are always triggered instantly when exposed to large fault currents by the magnetic protection.

They may be used to protect loads that use DC power as well as main circuits like photovoltaic batteries and inverters.

2. What is AC MCB?

Alternating current, also known as 60hz or 60 cycles per second, is what drives the power grid. The voltage alternates between +V and -V, changing 60 times per second. A voltage of 0 volts occurs 60 times per second at a certain point. The AC miniature circuit breaker will disconnect at this 0v point, extinguish the arc, and protect the circuit from excessive current.

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

3. Characteristic curve

When a low current circuit breaker trips, it is classified as type B (ticking 3 to 5 times the rated current), type C (ticking 5 to 10 times the rated current) or type D (ticking 10 to 20 times the rated current).

  • Type B MCB

This type of miniature circuit breaker trips at 3 to 5 times the rated current. These miniature circuit breakers 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 miniature circuit breaker trips at 5 to 10 times the rated current. These miniature circuit breakers are usually used to switch high inductive loads with high surges, such as fluorescent lamps and small motors. Thus, high-inductance commercial and industrial facilities are well-suited for them.

  • D type MCB

This type of miniature circuit breaker trips at 10 to 20 times the rated current. They are usually used for extremely high inductive loads with high inrush current. Therefore, it is suitable for X-ray machines, UPS systems, large-scale winding motors, and industrial welding equipment.

4. Miniature circuit breakers – AC vs. DC

The DC miniature circuit breaker has a higher arc extinguishing point.

In DC, the voltage is continuous and the arc is constant, which is more difficult to disconnect than AC miniature circuit breakers. The DC arc will not be extinguished automatically. This means that they can only be extinguished by cooling or mechanical interruption. Therefore, DC miniature circuit breakers must include other arc extinguishing measures: they usually have mechanisms to expand and dissipate the arc to simplify interruption.

Because AC currents alternate and their values are zero during each cycle, arc interruption is relatively simple. In every country, the number of alternating current cycles per second has been standardized, and in most cases it is 60 Hz or 50 Hz. The grid usually provides alternating current, while specialized industrial or battery applications often use direct current.

Please note!

There are certain types of miniature circuit breakers that can handle both AC and DC currents because the protection mechanisms are the same. However, it is important to verify that the current power supply type and MCB are always the same. If the wrong type of MCB is installed, it will not be able to provide effective protection, and electrical accidents may occur!

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

Only miniature circuit breakers marked with a DC rating can be used for the DC circuit. Never try to use an AC miniature circuit breaker in a DC circuit! The arc cannot be extinguished, and the wires will overheat and cause a fire. Don’t think that AC miniature circuit breakers can be used in DC circuits just because the amps and volts match your needs. On the contrary, do not use DC rated miniature circuit breakers in AC circuits. Note: Dual AC and DC rated miniature circuit breakers can be used (this will be stated on the manufacturer’s label). If both MCB and MCB meet the rated values, it will be clearly marked on the MCB, please check these values ​​carefully.

5. Application of DC MCB

Two MCB DC miniature circuit breakers are commonly used in the following applications:

1) Both gasoline cars and electric cars have automotive electrical components. Every vehicle has a DC MCB fuse box.

2) Uninterruptible power supply (UPS) systems usually use batteries. Even if UPS is supplying power to AC equipment, it must store energy in the form of DC power in the battery pack

3) DC Motor

4) Certain types of arc welding machines

5) Efficient LED lights

6) Battery-powered circuits, such as the use of battery-powered circuits in households where solar panels are installed in rural areas where there is no power grid. 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 miniature circuit breakers 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 DC and AC electrical equipment. For example, homeowners with solar panels can buy DC LED lights. In this case, a DC miniature circuit breaker must be used for protection. The remaining DC power can be converted into AC power by an inverter. Homeowners with multiple DC circuits have installed separate DC and AC power fuse boxes, each with multiple miniature circuit breakers.

7) Electric vehicles do not rely on fossil fuels at all, but use large-capacity rechargeable batteries. These batteries are used in turns with charging piles specially designed for electric vehicles. Since the system can work under DC, DC miniature circuit breakers must be used. It is 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 into alternating current to charge electric vehicles. The system provides completely environmentally friendly and sustainable energy for transportation.

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