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Hello all

wondering what you guys think of an idea that one of my electricians presented me with this afternoon

location: semi industrial kitchen

number of circuits ran to distribution board x 12 (they will be connected to 30ma rcbo units)

now the original idea was to install the classic switch bank 2 x 6way grid banks (obviously there was always going to be an issue with the cookers and hobs)(not sure what the plan was there lol)

however the plan presented today was , why cant we install a metal clad 12way distribution board (removing the main switch) so basically abusing the box cover and dim rail and filling it up with mcbs . and once marked up would act as a good isolation / switching point for the client

but this is where i ummmed and rrrred and thought i might need to do some homework. below is my immediate concerns

1)400/415v present in switch bank (can be labelled)
2)12x circuits within one switch ( i guess this could be labelled)
3) 12x circuits neutrals and earths in same terminal block (although they can be installed in order and i guess the same as the main feed distribution board
4)cooker / hob circuits tend to be double pole switches (i won't have this) but now wondering why ? do they have to be ?


ive prob missed some info out of my description , but hoping you guys get the idea

what you guys think?

ta
 
Hi,i suppose the first two things you need to know,are the functionality required for the switching,and the MI for the individual appliances.

Also,why are you allowing a group of sparks to brain-storm?

The result,will only be friction and injury ;)
 
thanks guys , i will try find out what kit they actually going to fit as you right might mention switching requirements recommended by manufacture , and yep always bad idea letting the guys think hahaha
and i think the idea of switching all off is ok , but thinking that when chief finishes cooking they might isolate hobs and stuff but prob leave dish washers on etc so guessing all for one might be an issue (maybe)
 
I think the overcurrent and functional switching should be separate. If they are combined, in the event of a fault causing a trip the user will attempt to re-energise the circuit immediately, maybe a number of times. Whereas if the overcurrent and functional switching are separated an investigation must begin, and upon finding an mcb has tripped questions as to why are raised and the necessary skilled person - an electrician - called in to find out why.

See also what Hager say on the use of mcbs for functional switching:

Circuit breakers used as switching devices - http://www.hager.co.uk/news-exhibitions-case-studies/news/amendment-3-to-bs-7671-2008/latest-news/circuit-breakers-used-as-switching-devices/50427.htm
 
Agreed - if there is a fault people will be flipping the MCB back on again and again, and/or it will go bang right under their finger tips when they aren't expecting it (an MCB can make quite a bang when you close it onto a short circuit and the magnetic trip fires). Then they will say the wiring is dangerous because the switch exploded, or something like that. Feels like a bodge even if it's technically functional.
 
number of circuits ran to distribution board x 12 (they will be connected to 30ma rcbo units)

...

however the plan presented today was , why cant we install a metal clad 12way distribution board (removing the main switch) so basically abusing the box cover and dim rail and filling it up with mcbs . and once marked up would act as a good isolation / switching point for the client

3) 12x circuits neutrals and earths in same terminal block (although they can be installed in order and i guess the same as the main feed distribution board

what you guys think?

Words quote in bold my emphasis.

For the these 2 reasons, it will not work. If you have 12 individual RCBOs going to 12 MCBs (lines) and a single neutral bar, chances of any of the RCBOs holding are extremely slim. And would not comply with 521.8.2.

Even assuming you did it the other way round (say, 12 MCBs in the upstream "proper" DB, then used 12x RCBOs as the functional switch) then this would not comply with 521.8.2 (between the MCBs and the RCBOs).

(And 521.8.3 scuppers it on a technicality, even if the above doesn't).
 
I missed the bit about sharing a neutral bar!

But on reflection, why are you proposing MCBs anyway? If you just want the convenience and ease of wiring of a DIN rail panel, why not use DIN-rail mounted isolators? You can get 1-module DP types certainly up to 20A, I think I've seen 32A. Above that you would have to go to 2 module width but is that a showstopper? I'm talking about units like https://uk.rs-online.com/web/p/non-fused-switch-disconnectors/7907434/
 
I missed the bit about sharing a neutral bar!

But on reflection, why are you proposing MCBs anyway? If you just want the convenience and ease of wiring of a DIN rail panel, why not use DIN-rail mounted isolators? You can get 1-module DP types certainly up to 20A, I think I've seen 32A. Above that you would have to go to 2 module width but is that a showstopper? I'm talking about units like https://uk.rs-online.com/web/p/non-fused-switch-disconnectors/7907434/
 
I missed the bit about sharing a neutral bar!

But on reflection, why are you proposing MCBs anyway? If you just want the convenience and ease of wiring of a DIN rail panel, why not use DIN-rail mounted isolators? You can get 1-module DP types certainly up to 20A, I think I've seen 32A. Above that you would have to go to 2 module width but is that a showstopper? I'm talking about units like https://uk.rs-online.com/web/p/non-fused-switch-disconnectors/7907434/
 
I missed the bit about sharing a neutral bar!

But on reflection, why are you proposing MCBs anyway? If you just want the convenience and ease of wiring of a DIN rail panel, why not use DIN-rail mounted isolators? You can get 1-module DP types certainly up to 20A, I think I've seen 32A. Above that you would have to go to 2 module width but is that a showstopper? I'm talking about units like https://uk.rs-online.com/web/p/non-fused-switch-disconnectors/7907434/
 
I missed the bit about sharing a neutral bar!

But on reflection, why are you proposing MCBs anyway? If you just want the convenience and ease of wiring of a DIN rail panel, why not use DIN-rail mounted isolators? You can get 1-module DP types certainly up to 20A, I think I've seen 32A. Above that you would have to go to 2 module width but is that a showstopper? I'm talking about units like https://uk.rs-online.com/web/p/non-fused-switch-disconnectors/7907434/
 
I missed the bit about sharing a neutral bar!

But on reflection, why are you proposing MCBs anyway? If you just want the convenience and ease of wiring of a DIN rail panel, why not use DIN-rail mounted isolators? You can get 1-module DP types certainly up to 20A, I think I've seen 32A. Above that you would have to go to 2 module width but is that a showstopper? I'm talking about units like https://uk.rs-online.com/web/p/non-fused-switch-disconnectors/7907434/
 
nota bene that Lucien Nunes in post #18 has suggested specifically a switch-disconnector by Schneider Electric which combines the roles of load switching and supply isolation.

Other disconnectors (aka isolators) are usually only rated for infrequent load switching(make or break), and then only when the load current is small compared with its rating and there is not the risk of significant voltage transients causing arcing across the contacts which cannot be cleared.
 

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