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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
    Do the rings have cable with only 1mm cpc?

    MCBs may not be compliant if this is the case.


    Terence.
  • 0

    Mark Mustard:

    I totally agree with the statement of using RCBO's entirely throughout the installation of a new board. As mentioned previously, if cost is not an issue then RCBO's would be a preffered option so as to minimise disruption of supply to the other circuits under any fault conditions. However, from experience, if I were to attend a fuse board with dual RCD protection and one of the RCD's had tripped and its associated MCB's were still in the on position, this would indicate without testing that you likely had a neutral to earth fault on that side of the board. If it was an individual MCB that had tripped then that would imply that the circuit was either overloaded or a short circuit fault had occurred. Wheras if an RCBO has tripped you are faced with the prospects of an earth fault, short circuit or overload! My point being, in some circumstances, having RCBO's can make fault finding a little more drawn out compared to a board with dual RCD protection. This however is my personal opinion, others may disagree and my approach is based purely on a visual inspection, prior to fault finding with a meter



    Are there any brands of RCBOs which indicate to show whether they have tripped due to Overload or to Unbalance (ie current to earth) so as to enable easier fault finding?


    Clive
  • 0

    Are there any brands of RCBOs which indicate to show whether they have tripped due to Overload or to Unbalance (ie current to earth) so as to enable easier fault finding?



    Certainly are - I've seen some Garo ones that trip to a 'centre' position for residual faults, all the way for overcurrent. Have flummoxed some people as they have to be switched from the centre position to fully off before they can be reset.

      - Andy.
  • 0
    MEM  61008 RCDs use the same tripping method. Centre off and tripped. To reset turn off then fully on again.


    This job appears to have been running for along time. I assume the house is now built? ..... lol.

    By the way, where have you put the smoke alarms and CO2 alarms? separate circuit or connected into existing circuits?

    I once put the house smoke alarms on the same circuit as the fridge freezer radial covered by a B16A RCBO. Still seems to be Ok.


    Legh


  • 0
    Clive, yes some RCBOs do differentiate as Andy AJJ states. The Garo ones and at least one other make do same, however an ordinary person might be confused by it - you ask `em and the are not sure. Like you I do prefer the all RCBO scenario but readily admit that mine (like many others) are a front end RCD covering all 12 circuits and has been like that since it was "in vogue" many years ago with no real problems encountered in practice (yet!)
  • 0
    The purpose of 30mA/40msecs earth leakage protection is to provide personnel protection in the event of contact with live parts.  So the ten RCBOs installed will still provide the required personnel protection to each circuit, even though the summed earth leakage may well exceed 30mA.


    Regards,


              Colin Jenkins.
  • 0

    Legh Richardson:

    By the way, where have you put the smoke alarms and CO2 alarms? separate circuit or connected into existing circuits?




    This is, IMHO, where "high-integrity" boards are useful (if not all RCBO). If the alarms are on their own circuit and RCBO, nothing other than a fault in the alarms or their own circuit will put them out of action.


    The counter argument is to use an adjacent lighting circuit so that the occupants are aware if the circuit has tripped.

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