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MCBs and MCCBs in the sub main Distribution Board

Nick Parker

I have a sub main distribution board which feeds the final distribution boards and 10's of individual loads.

Now considering that I have an option of applying both MCBs and MCCBs as the outgoing circuit breakers.

MCBs - Standard ratings are available from 0.5A to 80A.

MCCBs - Standard ratings are available from 0.5A till 2500A.

Can I have a mix of MCB and MCCBs as the outgoing breakers in the overlapping area till 80A? (In otherwords, for loads upto 80A, MCB will be used and above which MCCB will be used).

Note that prospective fault current at the sub main is less than 20kA. At 20kA both MCBs and MCCBs are available.

I'm sure many would have used this configuration. Are there any cons with this arrangement?

 

 

 

 

 

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    Nick Parker: 
     

    davezawadi (David Stone): 
     

    Is this a real design or a student job? MCCBs are much more expensive than MCBs, can have many more features, and may not be suitable for other or discrimination reasons. They are not normally available to fit in the same enclosures as MCBs, so final circuits will have their own distribution board. What is the submain rating and what are the outgoing circuit ratings?

    2d4d5d916bad18374e645c6ee3197e6a-original-mccb_mcb.png

    Q1 Should be all MCCBs if the first box is a MCCB panel board. I don't understand why the outgoing MCCBs are so small for such a big  supply. I am assuming that the 400A MCCB is set at 400A.

    For example, a 63A MCCB should be supplying the 63A distribution board. The distribution boards then will have MCBs as you have shown in the diagram. 

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  • 0

    Nick Parker: 
     

    davezawadi (David Stone): 
     

    Is this a real design or a student job? MCCBs are much more expensive than MCBs, can have many more features, and may not be suitable for other or discrimination reasons. They are not normally available to fit in the same enclosures as MCBs, so final circuits will have their own distribution board. What is the submain rating and what are the outgoing circuit ratings?

    2d4d5d916bad18374e645c6ee3197e6a-original-mccb_mcb.png

    Q1 Should be all MCCBs if the first box is a MCCB panel board. I don't understand why the outgoing MCCBs are so small for such a big  supply. I am assuming that the 400A MCCB is set at 400A.

    For example, a 63A MCCB should be supplying the 63A distribution board. The distribution boards then will have MCBs as you have shown in the diagram. 

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