Job description :-
- 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
