MCBs and MCCBs in the sub main Distribution Board

I have never installed an MCCB, but aren't they a different size from an MCB? And, therefore, they need to be fitted to different types of boards.

Discrimination between MCBs (regardless of rating) is typically non-existent - so I wouldn't have MCBs upstream of other MCBs if you want to have selectivity. So I'd go for MCCBs (or HBC fuses) rather than MCBs for distribution circuits even if is the rating is low. Perhaps for final circuits too if the load incorporates MCBs or similar protective devices that you'd need to discriminate with.

The enclosures for MCBs and MCCBs can differ - which might influence your choice depending on what sort of maintainability might be required. E.g. MCB enclosures are normally a simple boxes with a single common lid - so to access one outgoing device you'd need to expose just about everything - so H&S usually means that the entire board would have to be isolated before connecting in a new circuit or replacing a protective device - thus losing power to all the other circuits. In critical situations, some of the higher ‘form factor’ enclosures available for MCCBs have internal partitions and separate lids that can allow some safe working on one outgoing circuit while leaving all the other circuits live.

Also consider actual availability - i.e. what can be reasonably obtained from suppliers as distinct from what's in a manufacturer's catalogue. MCBs with a breaking capacity over 10kA are rare beasts in the wholesaler, likewise MCCBs below 16A. Promises that things can be ordered as specials often have small print that you have to order some ridiculous quantity or cost a fortune. Not just for initial installation, but on-going repair and maintenance. If something business critical unexpectedly goes bang, local availability of spares can become a surprisingly important issue.

   - Andy.

Thought MCCBs would need a Panelboard?

AJJewsbury: 
 

Discrimination between MCBs (regardless of rating) is typically non-existent - so I wouldn't have MCBs upstream of other MCBs if you want to have selectivity. So I'd go for MCCBs (or HBC fuses) rather than MCBs for distribution circuits even if is the rating is low. Perhaps for final circuits too if the load incorporates MCBs or similar protective devices that you'd need to discriminate with.

The enclosures for MCBs and MCCBs can differ - which might influence your choice depending on what sort of maintainability might be required. E.g. MCB enclosures are normally a simple boxes with a single common lid - so to access one outgoing device you'd need to expose just about everything - so H&S usually means that the entire board would have to be isolated before connecting in a new circuit or replacing a protective device - thus losing power to all the other circuits. In critical situations, some of the higher ‘form factor’ enclosures available for MCCBs have internal partitions and separate lids that can allow some safe working on one outgoing circuit while leaving all the other circuits live.

Also consider actual availability - i.e. what can be reasonably obtained from suppliers as distinct from what's in a manufacturer's catalogue. MCBs with a breaking capacity over 10kA are rare beasts in the wholesaler, likewise MCCBs below 16A. Promises that things can be ordered as specials often have small print that you have to order some ridiculous quantity or cost a fortune. Not just for initial installation, but on-going repair and maintenance. If something business critical unexpectedly goes bang, local availability of spares can become a surprisingly important issue.

   - Andy.

I was of the opinion that, it does NOT matter whether it is a MCCB or a MCB as long as the MCB meets or exceeds the prospective short circuit current rating.

I think that in the overload region, selectivity can be achieved while this cannot be achieved for higher short circuit currents.

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?

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?

M.C.B.s appear to to be best suited.

Z.

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?

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.