Energy Level in MCB

It's, it's ability to break current. On some large CB's it will be 100's KA

Fuses and circuit breakers include these characteristics, among others:

Max or peak short-circuit interrupting capability
Max or peak let-through current
Max or peak let-through energy

These are related, but not 100% correlated with each other (because of time, for one thing). Current is related with magnetic forces that may attract/repel busbars/cables to each other. Energy is related with heating/melting/vaporizing the same.

Bussmann Fuses has good literature on this, and some videos as well.

Please stand corrected. It should be Energy Limitation Class. You see, when there is a short circuit, the MCB will trip after certain milliseconds. Won't it? Upto the time the MCB trips for a short circuit, the short circuit current 'I' Amperes will flow for a duration of 't' seconds. There will be I2t energy let through the MCB and the downstream devices connected to this MCB must be capable of withstanding this "let-through" energy from the MCB.

Modern MCBs have a feature called 'current-limitation' wherein due to contact arrangement, there will be repulsive forces between the contacts and it does not require a sensing and signalling from a release to effect tripping of the MCB during a short circuit.

The high repulsive forces generated during the short circuit themselves would cause opening of the contacts. Thereby, current interruption takes place much before the fault current reaches the peak value. This is called current limiting.

When an MCB has the current limiting feature, the let-thro energy from the MCB is reduced and the downstream devices are stressed to a lesser level during a short circuit.

Based on the let-thro energy MCBs are classified under what is known as Energy Limitation Classes.

Hope it is clear.

By the by, forgot topost earlier! Aren't you the same "guest" who, of late, has been throwing a series of questions on MCBs? what's the plan? Planning to start an MCB manufacturing unit?

Humm have been wondering????