Answer / shan80

it depend upon the value of current flows during short
circuit.
And the short circuit current depends upon the KVA rating of
transformer how supplies that particular load and transformer
percentage impedance.

Answer / jitesh patel

we must know load of perticular equipment.
For Ex. Our load in MVA is 50 MVA
Our system voltage(MCB,MCCB,ACB) is 440V.

I(Bre)= 50/(1.73x0.440)=65.6 =Approx 65KA.

Our load in MVA is 20 MVA
Our system voltage(MCB,MCCB,ACB) is 440V.

I(Bre)= 20/(1.73x0.440)=26.2 =Approx 25KA.

Answer / ali

100A MCCB Bteaking capacity calculation

Answer / mohammed rafi

All above said suggestions are mere copy paste of something from wiki answer.its totally wrong.
Aforesaid calculations are to calculate rated current.
Short circuit analysis is to be done to calculate breaking capacity.

Answer / ashok

it depends on the short circuit & full load of equipment

Answer / ranadhir roy

We need to find out the short circuit MVA & based on this shortcircuit MVA , we need to calculate shortcircuit current .

Answer / sunil sethi

All are ok, but In industries generally 5MVA transformer they are using for a company load, then if we consider 5MVA is our load then Icu is 5/(1.732x440)=0.0065ka , please clarify, Is it ok please answer .

Answer / t s gupta

Breaking Capacity of MCCB is pre-calculated permissible amount of fault current (value of current can flow from contacts before opening/tripping the MCCB without damaging) which may facilitate the safe operation of MCCB and distribution transformer both.
It shall be calculated/derived from the distribution Transformer MVA rating and %impedance = kVA*100/ system voltage of load side * % Impedance rating
e.g. 20 kVA transformer with 5% Impedance, secondary voltage 440V i.e. 0.440 kV
Fault current Isc = 20*100/.440*5 = 10kA approx.

Answer / hrusikesh dehury

we must know load of perticular equipment.
For Ex. Our load in MVA is 50 MVA
Our system voltage(MCB,MCCB,ACB) is 440V.

I(Bre)= 50/(1.73x0.440)=65.6 =Approx 65KA.

Our load in MVA is 20 MVA
Our system voltage(MCB,MCCB,ACB) is 440V.

I(Bre)= 20/(1.73x0.440)=26.2 =Approx 25KA.

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