What are the points to be considered for MCB (miniature circuit breaker selection)?

1. Rated Current
2. Frame Size
3. Ultimate short-circuit breaking capacity
4. Operating short-circuit breaking capacity 
5. Rated working voltage
6.  Rated Insulation voltage
7. Rated impulse withstands voltage 
8. Utilization Category/ Characteristic: B,C or D curve
9. Number of Poles

First thing your load Current, then by knowing approximately your load current you will should be able to calculate the required short circuit current.

• MCB is miniature circuit breaker which is thermal operated and use for short circuit protection in small current rating circuit.
• Normally it is used where normal current is less than 100A.

MCB stands for Miniature CircuitBreaker. It is a vital circuit breaking component found in today’s modern electrical distribution system. It replaces earlier method of circuit breaking done via melting fuse wire. A melting fuse wire system is replaceable type of circuit breaking in which the fuse wire melts and permanently breaks the circuit upon an overload current event. Due to this hence it is quite cumbersome to each time replace and fix a new fuse wire. A miniature circuit breaker on other hand is reusable type of circuit breaking device that is nowadays widely used in homes and offices

I(L)x1.25=I(MAX) maximum current.

MCB specification is done on maximum current flow in circuit.