Wiring additional consumer units -a design question

[vwes59]

Hi,
I've got to put in an additional consumer unit into quite a large property and rather than daisy chaining them back to a single MCB in the main board which is RCD protected, I wondered if this a better solution: The property is served by TNC-S with an isolator switch.

Connect new tails into Henley block before consumer unit.
Connect these tails to their own main switch with a 100ma time delay RCD.
Run SWA or equiv to Garage/Workshop where the new CU will be located (It's about a 10m run)
New board will have RCBO's for the new circuits, one of which will eventually be connected to another CU in a summer house (another 10m run or so).

I'm hoping this satisfies the regs. The time delay RCD will protect the distribution circuit, ensure it complies with the regs that state any circuit should be protected by an RCD and shouldn't interfere with the RCBO's, thus solving any possible discrimination issues. Also means that if for any reason these new circuits have a problem, they shouldn't affect the main house, and only trip an RCBO, the time delay RCD should only trip if there is a problem with the distribution circuit.

Have I missed anything, or misinterpreted the current regs ?

 

[Mikegh]

I'm not sure you should be attempting this

Rcds and swa , I dunno

What we do here is branch off after main isolation and main overcurrent protection

 

[vwes59]

I'm not sure you should be attempting this

Rcds and swa , I dunno

What we do here is branch off after main isolation and main overcurrent protection

Lets see if my Competent Persons assessor agrees shall we before you make assumptions as to whether I'm competent or no !! Answer the question, don't make comments about me.

 

[telectrix]

the SWA does not require RCD protection on a TN earthing system. only if it's TT.

 

[Mikegh]

Lets see if my Competent Persons assessor agrees shall we before you make assumptions as to whether I'm competent or no !! Answer the question, don't make comments about me.

Apologies there I jumped in assuming you were diy

 

[brianmoooore]

Apologies there I jumped in assuming you were diy

I have to admit that the 'lack of basic knowledge' aspect of the OP made me assume the same.

 

[Petej999]

Lets see if my Competent Persons assessor agrees shall we before you make assumptions as to whether I'm competent or no !! Answer the question, don't make comments about me.

What comments about you are you speaking of??

 

[loz2754]

the SWA does not require RCD protection on a TN earthing system. only if it's TT.

It does however need overcurrent and short circuit protection, which will not be afforded by an upstream RCD, and the main cutout cannot be used for this. Better to use a switch fuse after the tails split in my opinion.

 

[MJPD29]

Why have you got a time delay rcd on it?