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How to wire up a consumer unit

Arran Cameron

A semi-detached house has a prehistoric fuse box with rewirable ceramic fuses. It will shortly be replaced with a modern consumer unit. The existing circuits are:



 



1. Lights



2. Upstairs sockets



3. Downstairs sockets



4. Kitchen sockets



5. Cooker



6. Shower



 



The following circuits will be added to the consumer unit:



 



7. Central heating



8. Burglar alarm and CCTV



9. Outside lights



 



I have been informed that the best choice is a split load consumer unit with two RCDs and space for RCBOs. My intention is that circuit 8 has its own RCBO but what is the optimal way to allocate circuits to RCD A and RCD B? Also, should any other circuits have their own RCBO?


  • 0
    Then of course there’s the requirement to undertake a risk assessment to see if surge protection devices are required.


    Before you know where you are this could be specced up to a fifteen hundred quid replacement consumer unit and you’ll need a extension on the side of your home to accommodate it,

    devil
  • 0
    RCBOs offer optimal protection, there are double pole switching ones and there are ones which discriminate whether it`s the RCD element portion or the MCB element portion of the RCBO which trips too.
  • 0
    Where has this come from all of a sudden? If it had been in this forum, I am sure that I would have remembered it. ?
  • 0
    One year, one hour and twenty minutes between posts.


    You thought you had blinked and missed something, actually either someone posted and deleted it or Ebee has been carefully considering his response.


    Andy Betteridge
  • 0
    Having read the complete post before realising the age of the OP I thought the criticism of the lack of guidance was unfounded as I believe it all depends.


    Today I would normally go for an all RCBO board unless the cost was prohibitive for the customer. I would also apply some basic analysis to the impact of a trip on the customer and recommend an appropriate solution. So a maniac experimenter may well get a different recommendation to a partially sighted OAP which would probably be different to the young family with many young children a couple of showers and washing machines going flat out. Whether they would take that recommendation is of course debatable when someone proposes a cheap one RCD solution for cash and let's forget about Part Pee.
  • 0
    An installation with ten 30 mA RCBOs could have a couple of hundred milliamperes of current running around the plumbing and earthing system without any RCD trips, whereas as the budget installation with one 30 mA RCD upfront would have shut down.


    Installing RCBO consumer units when it is apparent that there is issues with excessive earth leakage due to failing installation to spread the earth leakage across multiple RCDs is a bit dodgy.


    In a TT installation even with double pole 30 mA RCBOs a 100 mA RCD main switch serves a purpose.


    Andy Betteridge
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    Sparkingchip:

    One year, one hour and twenty minutes between posts.


    You thought you had blinked and missed something, actually either someone posted and deleted it or Ebee has been carefully considering his response.


    Andy Betteridge 




     

    Oh Andy you banged me to rights. LOL. This new  forum . I did not realise this was an old thread, I did not notice the 2018 in the date. I thought I was replying to a recent one.

    Anyway seasons greetings for all years past present and future. I reserve the privilege of still being a daft git
  • 0

    Chris Pearson:

    Where has this come from all of a sudden? If it had been in this forum, I am sure that I would have remembered it. ?




    Thinking further, this thread was started a year before the old forum closed and whilst, presumably, most of us were still active over there.


    I thought that the slightly off-topic debate about how whether standards should be openly available was interesting. Whilst I agree that as a general principle, knowledge should be disseminated, BS 7671 is not the sort of book which you can read from cover to cover and suddenly become an electrician. You need to learn how to use it.


    Regarding Asperger's (how's that for thread drift!) we aren't supposed to use the name anymore because he was associated with the Nazi party. Similarly, you might once have had Wegener's granulomatosis, but not any more for the same reason.

  • 0

    Sparkingchip:

    An installation with ten 30 mA RCBOs could have a couple of hundred milliamperes of current running around the plumbing and earthing system without any RCD trips, whereas as the budget installation with one 30 mA RCD upfront would have shut down. . . 


    . . . In a TT installation even with double pole 30 mA RCBOs a 100 mA RCD main switch serves a purpose. . . 




    Indeed, and I wonder how many overlook that. With 10 RCBOs, you could have something just short of 300mA of earth leakage, and nothing would operate, everything being within spec. In a TT system, that would give you a maximum earth rod resistance of 166 ohms or so. 


    Regards,


    Alan. 

  • 0

    In a TT system, that would give you a maximum earth rod resistance of 166 ohms or so.



    Indeed - however BS 7671's wording doesn't seem to require that - relating the required maximum RA to each RCD individually rather than to the sum total of all the front-line RCDs. I have tried to mention that in my response to a DPC or two, but don't seem to have been able to convince anyone...


       - Andy.

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