MCCB AND MCB

[MOSTAFA86]

I HAVE A 63 MCB IN A MAIN PB IN GROUND FLOOR IS FEEDING A 63 MCCB IN A FIRST FLOOR ITS A VILLA AND BOTH ARE 3P.
MY QUES IS CAN A MCB FEEDS A MCCB OF? AND IF IT CAN WHAT ARE THE CONDITIONS NEEDED TO BE DONE AND IS THERE IS ANY ARTICLE ABOUT THAT IN NEC OR IEC PLZ INFORM ME

 

[ScottyUK]

As posted in thread240-317941,

It can, but why would you want to? Waste of money, and you won't get any benefit of the higher performance of the 63A MCCB.

Is the CAPS lock on your computer broken? Either buy a new keyboard or stop posting until you fix it.


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If we learn from our mistakes I'm getting a great education!

 

[MOSTAFA86]

i wanna an article or something from any electrical codes that say it is ok to have a mcb replace a mccb

 

[ScottyUK]

I doubt you will find one.


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If we learn from our mistakes I'm getting a great education!

 

[jraef]

The difference is that, compared to an MCCB, if there is a fault in the circuit the MCB has a MUCH lower capacity to withstand the physical forces created by the fault current flow without blowing up and becoming shrapnel. Most MCBs are not rated for more than 10,000A (10kA) interrupt capacity, many MCCBs are good for up to 65kA, some even to 100kA. So consequently an MCCB will cost a LOT more money and take up a lot more room, it has to.

But if your system from the utility has an Available Fault Current (AFC) that is lower than 10kA (or whatever) rating of the MCB, then the MCB will be OK. If that is the case, then as Scotty said, someone wasted money buying an MCCB to go down stream from it, an MCCB will always have a higher IC rating than an MCB. The interrupt capacity in the circuit however is only as good as the weakest link, in this case the MCB.

If on the other had the AFC is greater than whatever the MCB is rated for and someone in the past replaced an MCCB with it, as I might expect, then that will be a dangerous violation of whatever codes are enforceable in your neck of the woods. It bears some serious attention to detail.

In either case you will not find a publication telling you what you want to hear, because apart from the waste of money, there is no rule against having a device that is seriously overqualified for the task at hand. So if like I said, the AFC is below the interrupt capacity rating of the MCB, then there is nothing inherently wrong with having the MCCB down stream of it.

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— Kilgore Trout (via Kurt Vonnegut)
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[GEORGE2311]

Have a look on those ABB discrimination tables attached. The case of MCB and MCCB is of course posible.



G.F.
www.engineering-services.gr

 

[ScottyUK]

George, those tables all assume the MCCB is the upstream device. I can't find any information relating to the situation where the MCCB is the downstream device. It isn't surprising because no one would intentionally design a system with an MCB protecting an MCCB.


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If we learn from our mistakes I'm getting a great education!

 

[GEORGE2311]

Thanks ScottyUK for your comment, you are right.I thought we were talking about an MCCB feeding an MCB. For residential applications the opposite is possible but you throw away your money.

G.F.

http://www.engineering-services.gr

 

[MOSTAFA86]

Thanks for ur help , i found that if both have the same ka its ok to be connected but in a limited applications in lv zones.