Discrimination and additional CU question

[Sparkboy]

I need to install a cu in a kitchen but wanted to make sure I got the discrimination right and hopefully also inside regs.

Main CU is in basement and is dual RCD, can I use a 32amp mcb on one side of the rcd and run t&e 10mm to the new CU in kitchen and use just a main switch with additional MCBs.

or

come off the main switch in basement with an rcbo.

or

would I need to put 10mm swa from an isolator off the Henley block, and then put another dual rcd board in the kitchen?

Thank you.

 

[Darkwood]

Always best to keep the rcd protection local to the circuits where submains are concerned ... mechanically protected run if required to avoid use of rcd on sub supply then fit 17th edition board in kitchen.

You can do any of the methods above although the Henley option would require you to put a main isolator in order to have one common isolation point for all electrics, having rcd protection in the basement can clash with circuit design regulations but been domestic you need to offer the pro's and cons to the customer on this one as its dependent on the set-up etc.

Remember if using 10mm T&E you may need to add additional earthing unless you can prove by calculation that the earth in the 10mm complies using the adiabatic Equation.

 

[Octopus]

Why do you want a 2nd board in the kitchen?

 

[Sparkboy]

Why do you want a 2nd board in the kitchen?

Dunno it was in the tender....

@darkwood thanks for that, so they would all comply?

i completely understand the nuisance of potential tripping and having to go to the basement...

so a 10mm t&e with potential additional earthing depending on the adebiatic (not sure how to spell that) with a non rcd board with main switch and MCBs, but the 10mm being fed from a mcb on one side of the rcd would be ok?

thank you.

 

[Octopus]

So you think feeding a 2nd board, in a kitchen, from a 32A MCB is a good idea?

Come off the main switch??

SWA - overload protection?

 

[Sparkboy]

So you think feeding a 2nd board, in a kitchen, from a 32A MCB is a good idea?

No what I think would be a good idea is to run a separate ring for the kitchen for low consumption items depending on load planning, and then separate circuits for the heavy items.

I was just trying to work out all options and pricing for the client... 45 amp, 32 amp whatever.

I always struggle with discrimination!

 

[Sparkboy]

Come off the main switch??

yes add a third busbar, neutral block

SWA - overload protection?

wylex do a 45 amp isolator

 

[Darkwood]

Dunno it was in the tender....

@darkwood thanks for that, so they would all comply?

i completely understand the nuisance of potential tripping and having to go to the basement...

so a 10mm t&e with potential additional earthing depending on the adebiatic (not sure how to spell that) with a non rcd board with main switch and MCBs, but the 10mm being fed from a mcb on one side of the rcd would be ok?

thank you.

As we don't know the potential circuits, the sub-mains run, the spare ways in the existing and whether it is high integrity (has un-rcd protected ways available) we can only give hints, you as the competent designer and installer need to have a good grasp of the regs... yes happy to help with small guidance here but show some willing and refer to regs and quote them to us to show your understanding then we can guide you the right way .... when i say they all may comply its not as plain and simple as that, its down to each installation and the layout and design as to which is most suitable and or whether the options you mentioned comply...

As murdoch has already commented on is their any specific reasons why a dist board is required --- even if spec'd id be asking questions to why as this adds a large cost, unless the layout of the premises makes it the method of choice to have a local Dist board.

 

[Darkwood]

yes add a third busbar, neutral block

If the DB is not designed to be expanded as such you shouldn't be adding extra busbars etc, refer to manufacturers guidelines or ring them but if it is say a split board with no non-rcd ways usually they shouldn't be adapted as such its bodgit and against regs as most manufactures will state clauses regarding alterations and additions to their equipment.

 

[Sparkboy]

Thank you, will get the book out later, I only got the tender an hour ago, everything else was straight forward, but just wanted to know if the discrimination worked.

If the DB is not designed to be expanded

Yes that is a necessity!

knowledge is power a guys.

Sparkboy

 

[Engineer54]

It'll have to be a damned good reason before i'd start providing satellite CU's in a standard sized house!!