Answer / mike evans

Circuit breakers are designed with withstand short circuit
currents for a short period of time, defined as Icw for a
period of 1 second. This is designed to guarantee
selectivity of breakers and other devices providing short
circuit current protection. The ultimate breaking capacity
of the breaker is the highest symmetrical short circuit
fault current that the breaker is designed to break, and the
breaker manufacture is required to guarantee this level of
performance for one time only. Ics or service breaking
capacity must be guaranteed at least 3 times.
Realistically, the value of Icu is not practical when
considering fault calculations in a distribution system, and
often manufacturers aim for achieving Ics=Icu.

Answer / ravikumar varatharaj

Icu - ultimate short-circuit breaking capacity
a breaking capacity for which the prescribed conditions according to a specified test sequence do not include the capability of the circuit-breaker to carry its rated current continuously
Ics - service short-circuit breaking capacity
a breaking capacity for which the prescribed conditions according to a specified test sequence include the capability of the circuit-breaker to carry its rated current continuously
Icw - rated short-time withstand current
The rated short-time withstand current of a circuit-breaker is the value of short-time withstand
current assigned
Icm - short-circuit breaking (or making) capacity
a breaking (or making) capacity for which the prescribed conditions include a short circuit

Answer / tad rybak

To my understanding Icm stands for Short Circuit Making
Capacity.
According to standard IEC 947-2 or BS EN60947, etc.
It is equal to 2.2 x Icu, where Icu means Ultimate breaking
capacity.

Answer / sagar

plz explain with exampie i cant understand

Answer / vyara

Ultimate or rated short-circuit breaking capacity
(Icn - EN 60898)
A breaking capacity for which the prescribed conditions,
according to a specified test sequence do
not include the capability of the MCB (Miniature Circuit
Breakers) to carry 0.96 times its rated current for the
conventional time.
Ultimate short-circuit breaking capacity
(Icu - EN 60947-2)
A breaking capacity for which the prescribed conditions,
according to a specified test sequence do
not include the capability of the MCB to carry its
rated current for the conventional time.
Service short-circuit breaking capacity
(Ics - EN 60898)
A breaking capacity for which the prescribed
conditions according to a specified test sequence
include the capability of the MCB to carry 0.96
times its rated current for the conventional time.
Service short-circuit breaking capacity
(Ics - EN 60947-2)
A breaking capacity for which the prescribed
conditions according to a specified test sequence
include the capability of the MCB to carry its rated
current for the conventional time.

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