# Thread: Designing of MCCB and MCB

1. Junior Member
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## Designing of MCCB and MCB

Please if someone tell me about the criteria while designing a feeder and branch circuit MCB and MCCB. I mean if am to design a circuit which consist of 4 sub circuit and each sub circuit feeding identical loads. The loads are 4 x 1.5 Ton A/c, a water kettel, Microwave, Refridgerator, exhaust fan and 4*36W lights*4. So my total load would be (4*2000 + 1000 + 750 + 500 + 100 + 4*144= 11KW or 20Amps 3 phase ). The supply here is 415/240V , 50Hz. Please help !

2. Senior Member
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Might be a little bit of a language thing going on that I'm not entirely sure what you're asking. I also don't know what's available to you as far as equipment or even what electrical standards you are following.

Personally I'd be inclined to a panel board with a main circuit breaker because in most cases here it is cheaper to buy them that way especially for small panel boards like you are asking about. I did not check your math but if you're 20 amps number is correct I'd be inclined to use a 60 amp panel just because that's probably the least expensive way to go.

In the US the national electrical code never requires a circuit breaker smaller than 15 amps so I would be inclined to make all the branch circuit breakers 15 amps. It's usually the smallest breaker you can get anyway for most panel boards although I have seen 10 amp Breakers.

Usually with 60 amp panels though there are a limited number of branch circuit space available so you might have to kick it up to the next size to get enough slots for all the branch circuit you want.

3. In places outside of North America, the decision to use an MCB (Miniature Circuit Breaker) vs MCCB (Molded Case Circuit Breaker) has mostly to do with your available fault current. MCBs are rated for much lower fault current capacity than MCCBs, generally no more than 18kA, as opposed to up to 100kA on some MCCBs. But most small DBs (Distribution Boards) are designed to use with MCBs up to and including 63A. Above that, it's always an MCCB as far as I know.

Here, very few MCBs are listed in a way that allows us to use them in other than as supplemental protection and even for those that are OK, there are no distribution boards that use them here.

4. Senior Member
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Also restrict design current to 80℅ of MCB/MCCB rating.

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