AC-DC

Arc quenching is more difficult with DC than AC, so AC MCBs might not be sufficient.

An AC breaker limits the current value and the voltage / current phase shift by adding an arc resistance in the circuit, which is usually highly inductive. Thus it accelerates the arrival of a zero of current, which appears anyway naturally at every half cycle.

In DC, there is no natural zero of current, therefore the arc voltage must be much more important ( and at the end reach an infinite value) to force the current to zero.

Short circuit interruption in DC is much more difficult in DC than AC, this is why manufacturers have different designs.

Of course, all this is mainly related to voltage, a 690 Vac breaker should work easily at 12 V DC ... and even a bit more ;-)

But , at equal voltage, chances are high than an AC breaker simply never interrupts a DC short circuit if important .. and explodes .

Under normal current carrying condition, there shall not be any problem though. When breaking short circuit currents, in DC applications, the AC MCB is highly de-rated as DC current interruption is quite challenging (you know! no current zeroes in DC as in AC). Moreover, the instantaneous release setting may have to be reviewed.

IEC code allows use of AC MCBs in DC circuits and provides derating that is necessary.