Difference Between DC & AC MCCB

I'm not absolutely certain but I think if you use any breaker in the incorrect application (AC vs DC or vice versa), the trip characteristics will not be correct. There may be other issues.

It's probably best to contact the manufacturer of the breaker(s) you intend to use. They would be the definitive authority on the application of their breakers.

i think u should go though abt MCCB application?

Most MCCBs have a DC voltage rating, but you must read it and understand it. There are limits to the DC voltage level that are different from AC voltages, and some designs may require you to loop one pole of the DC through 2 sets of contacts on the breaker in order to attain enough dielectric separation. If your MCCB does not show a DC rating on the nameplate, you cannot assume it has one, it may not.

Current is current though.

"Current is current though."

This is true regarding how thermal overcurrent trip devices react.

However, some MCCBs have a magnetic instantaneous trip coil used for motor circuit protection as opposed to just cable protection. The instantaneous trip coil may or may not be capable of reacting the same in either an AC or DC application.

The MCCB should be selected for the particular application if predictable and repeatable results within specific tolerances are required.

well friends i am working for siemens and we are using AC MCCB in the DCDB and 48V battery charger panels.As pointed out by raph the MCCB are 3 pole and we are looping 2 poles and hence making only 2 poles out of 3 poles for DC MCCB.

The consultant were very critical of this so we approached the MCCB manufacturer ABB and they commented it can be used but with a derating factor of 0.7875.

Also as pointed out by Joe its a thermo-magnetic AC MCCB i.e instantaneous magnetic + thermal characteristics.

But friends the question is whether it will quench the arc properly for DC circuit?is there a significant change in the operating mechanism from DC MCCB?

If circuit breakers are designed anything like switches with regard to load interruption, you are right regarding your concern for the ability of an AC breaker to quench the arc of a DC load.

Generally, switches designed for interrupting an AC load do not require the contacts to separate as fast as for a DC load since AC goes through a zero crossing every half cycle. The arc will be extinguished each time the voltage goes through a zero crossing, provided the load is not highly inductive. The contacts only have to get far enough appart to prevent re-flash. Not so with interrupting a DC load. Not only do the contacts have to separate quickly, there also has to be a means of quenching (cooling) the arc to extinguish it since there is no zero crossing.