Making and Breaking capacity of Circuit breaker

There are two types of currents which every electrical engineer must know before selecting a Circuit breaker.
These type of current are known as :-

1. Breaking current or Breaking capacity.
2. Making Current or Making Capacity.


You may visit also at link below for MCB Characteristics:-
http://electrialstandards.blogspot.in/2014/04/mcb-characteristics-and-applications-of.html

Breaking capacity :-

Breaking capacity of a circuit breaker or fuse is defined as the interrupting capacity of Circuit breaker or fuse that they can interrupt without destroying that equipment. The short circuit current which can occur under short circuit conditions should not exceed the rated breaking capacity of the apparatus. If breaking. Otherwise breaking of the current cannot be guaranteed.

Thus Breaking capacity of the circuit breaker refers to the maximum current in rms value the circuit breaker can interrupt.

Breaking capacity is also in the order of kA.

On MCCB’S Breaking current is specified on their name plate. Breaking current is what is taken in due consideration before designing any Electrical Systems.

Making Capacity:-

Making capacity of a circuit breaker is the maximum current which the breaker can conduct at the instant of closing. 

This making capacity is considered to the peak value of the first cycle when there is an imaginary short circuit between the phases.

When there is a short circuit in the line and the breaker is closed, the peak value of the first cycle is the most severe from an electrical perspective. 

Making current value is in kA. 

The making capacity is expressed as a peak value as the dc offset during fault conditions is taken into 

account.

The making capacity of the circuit breaker is usually greater than the breaking capacity of a circuit breaker as breaking an electric circuit is difficult due to arcing which occurs and which has to be quenched.

Making Current is usually 1.5 to 2 times greater than breaking current.

Though Making Current isn't specified on MCCB name plate but Making current is more important for design aspect and design companies must take due care of Making current before designing the MCCB.

To know about direction of fault current visit at:-
http://electrialstandards.blogspot.in/2014/04/fault-current-direction.html