Distribution board or main switchboard

[Indy]

Hi,
With regards to bs7671 are there any rules regarding when to install a distribution board?
For example say we have a main switch board that is feeding pieces equipment separately but these pieces of equipment are quite local to each other would it then be better to take one feed from the main switchboard and then install a DB to feed the pieces of equipment or feed them separately from the main Switchboard ?


Thanks

 

[che12345]

Dear Mr. Indy
1. "...With regards to bs7671 are there any rules regarding when to install a distribution board? "
No. BS7671 is concern on the [safety] of the installation. There can be numerous [acceptable] alternative ways in achieving the optimal and safety end result.
2. "...say we have a main switch board that is feeding pieces (of) equipment separately but these pieces of equipment are quite local to each other would it then be better i)to take one feed from the main switchboard and then install a DB to feed the pieces of equipment or ii) feed them separately from the main Switchboard ? "
Usually alternative i) would be cheaper, the preferred. Consider 3. below.
3. Attention! alternative i) has this disadvantage: when the [branch MCCB*] on the (Main board)* or the [MCCB or isolator]** on the (incoming of the DB)** trips, ALL the pieces of local equipments would blackout! This can be serious;[unacceptable] if it is feeding all the lighting loads in a super-market, for example. Alternative ii) usually higher cost, circumvents the setback; if the loads are fed (separately) by [individual] MCB from the Main board.
Che Kuan Yau (Singapore)

 

[charz]

Can MCCB and MCB be put in the same sub distribution panel?

 

[che12345]

Dear Mr. charz (Electrical)19 Oct 21 07:23
" Can MCCB and MCB be put in the same sub distribution panel? "
Yes, can. It is very often the incoming is a MCCB, while the outgoings are MCB. Do you have any reason or what is your concern?
Che Kuan Yau (Singapore)

 

[charz]

Do you have any reason or what is your concern?

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.

My concern is the selectivity issues between the Upstream MCB to downstream MCB and the Upstream MCCB to downstream MCCBs / MCBs.

 

[che12345]

@ Dear Mr. charz (Electrical)19 Oct 21 10:44
"...1) I have a sub main distribution board ....Can I have a mix of MCB and MCCBs as the outgoing breakers.... Note that prospective fault current at the sub main is less than 20kA. At 20kA both MCBs and MCCBs are available....2(My concern is the selectivity issues between the Upstream MCB to downstream MCB and the Upstream MCCB to downstream MCCBs / MCBs...."
1. YES, you can have any number of MCCB and MCB in any board.
2. There are selectivity issue between MCCB and MCB, also between MCBs of different current ratings. Check out the information from the catalogue for detail on [selectivity]. It could be [partial] up to certain kA level or [full].
Attention: The manufacturer's table is good for [his product only]; NOT for other brands or a mixture.
Che Kuan Yau (Singapore)