I had an electrical fault that tripped my RCCD that I was querying a couple of days ago but I have a another slightly related question. It would make sense to put the kitchen on its own ring, so in the future only the kitchen would be isolated if there was a fault but will I have shed loads of problems getting this approved. A guy at work is having a new consumer unit fitted and the electrician passing the work off has failed it because other work done donkeys years ago isn't up to current regs, too many junction boxes in the ring. If I now fit new wiring and an extra mcb in the consumer unit and go to get it approved can it be failed because the existing wiring in the kitchen is up to latest regs?
Replacing a consumer unit involves work on all the circuits it feeds, so does bring all those circuits under scrutiny. (That said, there's no limit on the number of junction boxes in a circuit, provided they're all sound and accessible, and that voltage drop and Zs requirements are met. Perhaps the tester thought that "good workmanship and proper materials" had not been used.)
The work, and the required electrical installation certificate, only concerns the new circuit, which must comply with BS 7671. The supply to the consumer unit, i.e. the suppliers works and meter tails must be suitable for any additional load. There's a space on the electrical installation certificate for comments about other parts of the installation, but, unless anything grossly dangerous is found, you're unlikely to have any difficulty. Make sure the main earth bonding to water & gas etc. is up to scratch though.
If your new circuit includes re-use of any existing wiring then the latter will need careful assessment to make sure it's OK.
For a kitchen ring, in particular, you must be aware of regulation
433-02-04, which says the following:
"For a ring final circuit protected by a 30 A or 32 A protective device complying with BS 88, BS 1361, BS 3036, BS EN 60898, BS EN 60947-2 or BS EN 61009-1 (RCBO) and supplying accessories to BS 1363 and wired with copper conductors, the minimum cross-sectional area of both phase and neutral conductors is 2.5 mm^2 except for two-core mineral insulated cables to BS 6207 for which the minimum is 1.5 mm^2. Such ring final circuits are deemed to meet the requirements of regulation 433-02-01 if the current-carrying capacity (Iz) of the cable is not less than 20 A, and if, under the intended conditions of use, the load current in any part of the ring is unlikely to exceed for long periods the current- carrying capacity (Iz) of the cable."
(Note the last three lines in particular.)
Also if the ring is feeding sockets which are likely to be used to supply portable equipment outdoors, it will need to be RCD protected (at
30 mA). This will apply if the kitchen is on the ground floor and there isn't any more specific provision for running extension leads outside.
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