What is difference between AC MCB and DC MCB?


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.

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.

Difference Between AC MCB and DC MCB

  • In DC, the voltage is continuous and the arc is constant, which is more difficult to disconnect than AC miniature circuit breakers.

  • There are certain types of miniature circuit breakers that can handle both AC and DC currents because the protection mechanisms are the same.

  • 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

  • If the MCB is looked for the difference between AC MCB and DC MCB by only physical parameters than the AC MCB has labels of the terminals as LOAD and LINE terminals whereas the DC MCB will have positive (+) or negative (-) sign on its terminal

  • It is harder to break a DC MCB as compared to an AC MCB. AC MCB is extinguished with the help of zero crossings but a DC MCB is extinguished with the help of a mechanical interruption or with cooling. DC MCB’s open faster as compared to AC MCB’s.

  • Breaking a DC current is harder than breaking an AC current. When contacts open, an arc is drawn. N AC this is usually extinguished by the zero crossing, but DC arcs are not self-extinguishing. This means they can only be extinguished by cooling or mechanical interruption. DC switchgear – MCBs, switches, starters etc. – has to open faster and further than AC, and may incorporate Air blasts or moving mechanical shields to interrupt the arc.

  • 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.

Can AC MCB use for DC?

The AC current or signal is continuously changing its value for each second. The voltage of the AC signal changes its polarity from positive to negative in every second of a minute. The MCB will break at 0 Volts and the arc will be extinguished and as a result, the wiring will be protected from a huge amount of current. Whereas the DC signal is not alternating, it flows in a constant state and the value for the voltage is only changed when the circuit is turned OFF or the circuit input is decreased by some value otherwise the DC circuit will provide a constant value of voltage for each second of a minute. So, as there is no 0 Volt point in a DC state so the AC MCB will not work with DC states.

Application of DC MCB

  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

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