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Consumer Unit Single RCD incomer acceptable?

PG
Would the Forum like to comment/propose a reasonable, effective, compliant alternative approach?

Job description :-
  1. Relocate Cooker Isolation Switch.  Joint, run new section of cable and fit new Isolation Switch.

  • Add new S.O. to kitchen worktop layout by extending existing Kitchen RFC. Add Switched Fuse Spur for Extract Hood.

The property is an average sized 2 bedroom flat (no internal stairs), wired in the late eighties/early nineties, using a Crabtree SB6000 MCB C.U. The TN System wiring was carried out to a good standard, remains in good condition with all Zs low (well within ADS requirements). The C.U. has the following circuits – Cooker (32A), Kitchen RFC (32A), Boiler Flex Outlet (16A), lighting (6A), 1No unused space. Crabtree has advised that there are no available/suitable replacement MCBs or RCBOs.
I considered an option of not adding an RCD on the basis that there was no possibility of using the S.O.s for outdoor use and the alterations would not leave the installation in a worse state. An approach that was not fully compliant with current requirements but avoided selectivity questions. As I had added a S.O. and buried T&E cabling I felt that I had to add RCD protection in accordance with current requirements. This was achieved by inserting a 30mA, AC RCD in the C.U. tails (411.3.3 & 522.6.203).
This doesn’t follow the trend of separating the circuits on two RCDs or individual RCBOs but I felt that there wasn’t any danger or extraordinary inconvenience that would require some form of further division of circuits (314.1 & 314.2). I didn’t spot anything in 531.3 (Residual Current devices) or 536.4 (Selectivity between RCDs and downstream OCPD) that would prohibit the arrangement (I await correction ?).


Thanks

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  • 0

    Sparkingchip:

    Not wanting to replace a thirty year old consumer unit that is no longer fit for purpose when a 5-module consumer unit with a main switch and three RCBOs for less than a hundred quid plus labour will bring it up to current standards is just being tight.

    . .. .. . … .

    This arrangement is okay, but it’s not a job to be taking photos of to promote your work.


    Andy B.



    Andy, I agree that hardware cost differences are not large.
    As a rough estimate, taking the adopted single RCD solution as the basis for hardware cost;-
    The downstream two, single pole, RCBO option would be about £20 dearer.
    The new C.U. option would be about £35 dearer.
    Although the new C.U. is not significantly dearer from a hardware perspective, it would involve the extensive inspection and testing of the complete installation giving an overall project price increase of about £200.
    Quite significant when considering the original scope.
    There are a number of Registration Body, ESF documents that caution against “over-zealous” coding and unnecessary changing of C.U.
    For similar circumstance in the future, I think I’ll continue to hover between the single RCD and the downstream RCBOs.
    Thanks
Reply
  • 0

    Sparkingchip:

    Not wanting to replace a thirty year old consumer unit that is no longer fit for purpose when a 5-module consumer unit with a main switch and three RCBOs for less than a hundred quid plus labour will bring it up to current standards is just being tight.

    . .. .. . … .

    This arrangement is okay, but it’s not a job to be taking photos of to promote your work.


    Andy B.



    Andy, I agree that hardware cost differences are not large.
    As a rough estimate, taking the adopted single RCD solution as the basis for hardware cost;-
    The downstream two, single pole, RCBO option would be about £20 dearer.
    The new C.U. option would be about £35 dearer.
    Although the new C.U. is not significantly dearer from a hardware perspective, it would involve the extensive inspection and testing of the complete installation giving an overall project price increase of about £200.
    Quite significant when considering the original scope.
    There are a number of Registration Body, ESF documents that caution against “over-zealous” coding and unnecessary changing of C.U.
    For similar circumstance in the future, I think I’ll continue to hover between the single RCD and the downstream RCBOs.
    Thanks
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