Electrical Question

Normally MCCBs are not designed to trip on unbalanced conditions. Maybe there are some specific designs which are meant for motor protection, which may have a built-in unbalanced trip system. In thermal trips, it is achieved by a differential slider mechanism, similar to thermal overload relays. In electronic releases, the microcontroller can be programmed to sense unbalanced currents and trip. As to what is the threshold, it is the designer who decides this. For thermal overload relays, there is a spec... the relay must NOT trip when two phases carry 100% and the third phase carries 90%. And it MUST trip when the the current in the third phase is reduced to Zero, at the same time the current in the other two phases is raised to 115%. This is as per IEC 60947-4. The same may be taken for motor-protection MCCBs also. Most designs do better than what the IEC specifies though.

And one mild suggestion...do not use all capitals in this forum..CR4 frowns upon this.

Generally MCCB will not trip when there is unbalanced current. MCCB have magnetic relay for over current /short circuit current protection & thermal relay for over load protection.For motor protection MCCB have only magnetic protection for over current & a seperate thermal relay used for over load & missing or unbalanced phase and a contactor for control & switching.

I suppose your MCCB is having a micro-processor based protection release in which you have got this unbalance protection.