Can we use AC MCB on DC Circuit?
I have seen many sites that they have mentioned that we cannot use AC MCB on DC circuits. is it really true? It is not true. Their explanation is wrong. Let me explain in details.
For Understanding, what inside an AC MCB? one thermal-based overload trip mechanism and another one are a magnetic-based trip mechanism for short circuit trip and these two contributing for tripping.
Does Overload trip of AC MCB Works DC circuits:
Yes, overload tripping is nothing but a bimetallic strip and it designed with withstand (No physical state change) underflow of normal rated current. when the current flow is higher than the rated current, the bimetallic strip melts and it releases the tripping mechanism and the circuit will be open circuit.
The same instant will happen while flowing DC current. In fact, DC current trip the MCB better than AC current. Hence, the overload function works on DC.
Does Short circuit work on AC MCB for DC current?
Yes, look at the picture there is a thin copper wound coil and a small piece of the plunger is placed inside the MCB, which is used to trip the circuit on the occasion of short circuit fault. It is magnetic tripping.
The functionality is simple, under normal rated current, the coil creates slight alternating magnetic field but that is not enough to pull the plunger top operate a trip mechanism. But during the fault condition, the coil creates a strong magnetic field and pull the plunger, trip the MCB.
But in the DC circuit, the steady magnetic field will be created. Under the fault condition, the MCB coil creates a steady magnetic field and which pulls the plunger, trip the circuit.
That’s all. The functionality is the same.
Hence we can use AC MCB for both AC and DC circuits.
I have used personally, It worked well.
Now you get another doubt, does earth fault function works on DC?
No, if the AC MCB has earth fault tripping means, that function does not work on DC. Since for earth fault, inside Current transformer does not generate output for DC current.