effective breaking capacity (KA)

I Have one thing to clarify my dear friends regarding the breaking capcity of MCB.To my knowledge there are MCBs with 35 KA and 50 KA also it available with ABB S 800 Series breakers which are mainly used in wind mill segment

Are you sure that it is only an MCB (Miniature Circuit Breaker)? It could be an MCCB (Moulded Case Circuit Breaker).

If an MCB can clear 35kA and 50kA it ca no more be called MINIATURE.

Please confirm.

@ Electricalexpert 65.

below are the concluding lines of your last thread.I was thinkin after takin the length of cable in to consideration the breaker's breaking capacity will be less because of the limiting impeadance of the cable,pls am not very experienced can u please elaborate on your point.Thank you

Alternately, if the downstream breaker is located after the cable, then you have to calculate the fault current at the end of the cable length, duly taking into account the impedance of the cable. Then the breaker's breaking capacity is equal to more than the fault level at the location.

Let me explain!

Suppoisng right under the MCCB the fault level is, say, If1, then the MCCB should have a breaking capacity more than If1.

But, after a length of cable, the fault level would be, say, If2, which is less than If1, then the MCCB's breaking capacity should be more than If2. That is what I meant too.

Thank you very much.

I felt after the length of cable,the breaking capacity of the present MCCB should be equal to If2,because if its higher than If2 the MCCB might not trip for a fault that is not as high as If2+x,instead it will allow fault current to pass through it.Pls correct me if am wrong.Thank you very much for your kind response.

Please understand that Breaking capacity is one thing and the Release Setting is another thing. Even when you have a 1000A, 50kA Breaking capacity MCCB, the short circuit instantaneous relesae settings can be set from 2000A itself. So, even when the current is more than 2000A the MCCB will trip. This is the sensitivity of the MCCB's release. Whereas the capacity is its "Strength". Any breaker is capable of breaking any current from its rated current upto its ultimate breaking capacity.

Even in the present case, the present MCCB can still have a breaking capacity equal to or more than If1 and the release setting can be set less than If2; that way it migt even trip for a fault downstream of the cable, provided time delay is available in the short circuit release. Otherwise it is not preferable to trip the present MCCB for faults at If2.

Thank you very much, your explanation sank deep into my my head.last week i posted a thread as regards earthing and no one has commented on it, can u please help me check it out and let me know what u think.Thanks

I will try to locate that thread. Or may be you can repost it.

how do i test the effectivness of an earth grid from its concrete test well?and is it necessary i take my earth conductor through the piles b4 driving it to the ground when the design shows that an earth mat will be made 1metre into the ground that will help to effectively earth all the associated equipment and machines.This earthing is actually meant for a 250MW gas power plant.The client insist i must earth all foundations b4 casting is done, but i feel i should stick to the design concept,which means i'll only take my earth conductor through foundations that will obstruct my earth mat in the future.

What is a pig tail.

Hi all

just to add MCB Miniature circuit breaker ==<100A

100--1000A it is moulded case CB MCBs

for short circuit like this it is MCB as you can also have >100A

then Take the cable reactance and use it with available short circuit

make sure you have cable damage curve while performing this .

good luck with calculations