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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?


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    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
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  • 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
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