RCD as main switch to self contained flat supply CU

[craig1000]

Hi all just a quick one, what's are view on using 63a, 30 ma RCD as the supply to a self contained flat CU within a house?
Basically im doing CU change & remedial's after EICR, many circuits so gona need large CU or 2 * 10 way split load, 1 for the household standard circuits & separate for external he wants now & in future.
Separate CU in flat, am adding RCD protection to this bur also want to RCD protect the 16mm T+E going up so was thinking time delayed RCD. Thought's on coming direct off this with 16mm or as im going to be using wylex & largest mcb they do is 50amp, & have a 9.5kw shower up there (50 amp mcb), 1 ring (5 sockets) & 1 lighting circuit (350 watts) so would prefer to go to a 63amp supply to flat rather then the 50amp i can get.
would using the 63amp 30ma time delay RCD be OK or would you install mcb after it.
Was thinking of making the external a split load too & using one side for externals & other side for flat.
Can then use other CU for the rest of the house.
will be looking into the regs properly tomorrow but just thought id pop the question up & get some thoughts?

Cheers in advance!

 

[Deleted member 26818]

If the 16mm² T&E requires RCD protection, because it is concealed in a wall.
Then a time delayed RCD would not be acceptable.

 

[craig1000]

Hhhmmm ah ok then! As I said I shall be looking into regs tomorrow, new to domestic! Do you have any suggestions? I am assuming it needs rcd protection even though a distribution circuit as it is concealed within a wall? Don't want to use a normal one as the self contained flat shall need one on it's cu to prevent a-having to go to the main house garage to reset if it trips & b it tripping any of the house!

 

[Deleted member 26818]

Unfortunately, the RCD will have to operate within 40ms at a current 150mA and above, so a time delay won't cut it.
You could use SWA, flexishield (or similar) or perhaps some earthed conduit?

 

[craig1000]

Existing install Cable runs around garage & then disappears up through ceiling into bedroom or bathroom & then up to loft, before it reappears so re cabling it isn't an option as far as the customer is concerned, the usual well its working OK now, what's wrong with it. They don't want to pay to fix something that in there eyes isn't broken ;-(

 

[sedgy34]

So it's an exhisting cable you havnt installed? Rcbo it then to save any inconvenience

 

[malcolmsanford]

Whether it's an RCBO or a combination of RCD/MCB it still will have to technically, and to the regulations, be 30ma.

Craig you really are between a rock and an hard place, and in the real world. Rightly as you say how can you say to a customer that something that was installed before the 17th edition and as worked safely and without problems for all these years is now "not safe" and needs to be ripped out and replaced or that you have to now make the installation less efficient, though possible safer.

There really isn't any real get out via the regulations though in the introduction part of the regulations on page 4 can be read, as the entire book, in various ways.

Existing installations that have been installed in accordance with earlier editions of the Regulations may not comply with this edition in every aspect. This does not mean that they are unsafe for continued use or require upgrading


You are upgrading the protection devices as in doing a CU change, but your leaving the existing installation as is, so can you say that your distribution circuit is not affording RCD protection would come under may not comply with this edition in every aspect, or do you have to rigidly say that as your upgrading the CU to omit RCD protection from the existing T+E is a serious non compliance ??

For me there is no easy answer. IMO if the circuit which was installed --- years ago tests to be safe ie IR, Zs etc then why not omit the additional protection by RCD, after all the regs are not statutory, you would be leaving the circuit in this case worse than it is now, by inconvenience of a future trip, you have proved that the circuit is still fit to use and safe.

And I would imagine 999.999/1.000,000 there would never be a problem and no one would ever know , but unfortunately you may be the victim of the one time. I'm afraid it is your call. As the designer you could omit the RCD and give a rake of reasons and results why, but today the RCD is god and omitting it will leave you open to problems if something happened.

 

[richy3333]

If it's any consolation I had a similar(ish) situation recently. Existing supply cable from main DU to a sub CU. Renewing CU but not the cable. Existing cable not RCD protected. I queried situation with the NICEIC and they said that because the cable was existing and not part of my work then I could leave off the RCD protection - as MAlcolm more eloquently says above

Others may not agree, but if my Scam provider agrees with it and I have noted it in the customer file then that's good enough for me come assessment day.