Adding RCBO or RCD to CU?

Discussion in 'Electricians' Talk' started by KlausK, Oct 10, 2020.

  1. KlausK

    KlausK Member

    Hi, I am fitting an external floodlight and understand that it would make sense to add an RCBO to the lighting circuit that this runs off - is this a notifiable event?

    I already have a mix of MCBs and RCBOs - with the RCBOs protecting my two socket circuits. I am wondering if it would be better to fit a 100A RCB and shuffle the MCBs along, to take a busbar coming out of the RCD? The biggest practical issue that I can see with that is that all of the RCDs that I have found have the live on their LHS and the neutral on the RHS. This would make the busbar pass immediately under the neutral outlet, with potentially disastrous consequences. First - am I talking total b*ll*cks? Would I even be permitted to do this myself? And are there any RCDs that have the live on the RHS?

    I realise that the answer to the first question may make the others irrelevant, but I'd like to make things better if I can - and I can't afford to replace the entire CU.
  2. terrymac

    terrymac Screwfix Select

    If you have RCBO protecting a socket circuit ,run a spur from it to a fused connection unit and connect your outside light to the fcu.
    And forget working on the consumer unit yourself.
  3. unphased

    unphased Screwfix Select

    I think you are completely confused about what you want to do. Much of what you ask shows a complete misunderstanding. Why would you, for example, want to use a 100mA RCD?
  4. KlausK

    KlausK Member

    Nice idea, but there's already an external light fitting in place, complete with a switch indoors (and no nearby socket). I was going to add the RCBO in the spirit of extreme caution.
  5. Banallsheds

    Banallsheds Well-Known Member

    He said 100 amp RCD not 100mA.
  6. unphased

    unphased Screwfix Select

    Oh. Why 100A then? 80A or 63A perfectly ok.
  7. KlausK

    KlausK Member

    I didn't say 100mA - I said 100A. 100A is a rough total of the current limit of the remaining MCBs. It's also the rating of the main switch for the CU.

    Accepting that I may be totally off track, as indicated by my first question.
  8. KlausK

    KlausK Member

    I'd be more than happy to go for a lower rated RCD, but I think my questions would be pretty much unchanged otherwise. MCBs are 32A + 16A + 5 @ 6A = 78A, so 80A would be fine.
  9. unphased

    unphased Screwfix Select

    You don't understand enough to be doing this. I would advise getting an electrician It took me 4 years of college and 17 years in the trade to know the answers. Can't explain all that in a forum post.
  10. unphased

    unphased Screwfix Select

    All we will do is fall out, like we are doing.
  11. KlausK

    KlausK Member

    OK, I'll leave it there then. Sometimes these conversations help and sometimes they don't but so far you haven't actually noted anything wrong in what I asked.

    Over and out.
  12. KlausK

    KlausK Member

    We haven't fallen out unphased, there's bigger fish to fry in the world at the moment. Just glad to be alive. Keep well :)
  13. unphased

    unphased Screwfix Select

    Sorry, I can't help you. You too.
  14. MGW

    MGW Screwfix Select

    I am lucky money was not a problem so fitted a whole new consumer unit, but I see what your thinking, looked at your profile to see if your are local so I could donate old units. But unlikely as I live in Mid Wales.

    So first question are you permitted, well the laws are so poorly written can't say, are you an ordinary person? If not then you and use any distribution unit, it does not need to be type tested, if not classed as a consumer unit then can you fit it? It would be up to the courts to decide, and unless you kill some one, it is unlikely to go to court, so the main thing is don't kill or injure anyone.

    So what is a RCB? think tipo and mean RCD, in my old house 1992 I fitted two RCD's each one feeding a Wylex fuse box with fuses swapped for MCB's this was well before 2004 and Part P. And well before RCD in the home was common, we were still replacing the old ELCB-v which I found last one in 2017 so guess still some around.

    So you can't really do it any more and comply with Part P and IET/BSi BS 7671, but you can do it. As to if you want to do it is another thing. I agree if seems completely daft to say you can't make your home safer by adding RCD protection because some silly law says you must register the work, however on a forum it is hard to say forget the law as will end up just getting banned.

    There is nothing stopping you from doing as I did and using an adaptable box to house the RCD, but clearly it will not comply, however much it seems sensible to add RCD protection the law says if you do it DIY then you must get the LABC to inspect and pass what you have done, in Wales that means £100 plus vat, so if short of cash then non starter.
  15. KlausK

    KlausK Member

    Thanks MGW - my daughter-in-law is a lass from Rhayader - lovely part of the world! :)

    Yes, the RCB was a typo - meant to say RCD, as I repeated all other times (typical!)

    My house dates from 1967 and did not have any RCD initially. We had our kitchen re-fitted a few years back and the electrician suggested replacing a couple of the MCBs with RCBO (downstairs sockets and kitchen sockets). Since I was working on the outside light, I though I'd add some further protection for that, by essentially repeating the process for the downstairs light circuit. I may just add an RCBO, and think about adding a high current RCD to sit upstream of the MCBs, but I'll prob wait until COVID has passed, when I'll be more comfortable inviting an electrician into my house to check it out. I'll probably go for the guy who did my kitchen work, since I know and trust him.

    I've been dabbling with electrics since I was around 14 and I'm 60+ now - my father taught me a lot and I've picked up more along the way. But clearly I'm not formally trained, which is why I reached out on this site. Most professionals are happy to help, while others are more cautious and explain that things are best left to an expert. As I've seen elsewhere - a drop of water won't kill you, but a drop of 240v just might... Better safe than sorry! I have had the odd 240v kick - e.g. when I touched a wire to see if it was live. I was only a youngster then, and it's not something I'd like to repeat. I've got an old telephone dynamo, which can pump out 100V quite easily.

    Keep well - these are curious times we're living in. Wales is suffering badly :-(
  16. MGW

    MGW Screwfix Select

    Lucky not my part of Wales, but it has put the brakes on selling old house, I have some push bike dynamo's but their not actually dynamo's, I suspect 1930's they were, but mine are all alternators, but talk about a hub alternator and people look at you as if your daft, I would love to get one of those tubes that took batteries and find out how they worked.

    But yes stuff with my house is on hold, one because old house not sold, a little short on cash, and two I want to see what I am buying, three stuff simply not available, before lock down realised I had made an error, and fitted type AC RCBO's not type B as it said on the box, I want type A, but in real terms only the socket supply is likely to be a problem with shocks, so decided to just swap two RCBO's to type A, three weeks ago went to whole sale outlet and apologised for not picking them up, only to be told still on back order.

    So yes it seems better to wait, unless a MK consumer unit as it seems they have announced they are stopping making them. 1967 you just scrapped into having cpc to lights, rules changed in 1966. However using RCBO seems odd, even in 1979 when last house built the fuse box was Wylex and although you can get MCB's to replace the fuse, there was no provision to fit any RCD protection.

    BS 7671 has a design date when it applies from, if re-designed, then clearly the date of re-design applies. So when in mothers house in 2004 an electrician fitting a shower in a wet room offered to swap the old Wylex fuse box for a modern consumer unit with some RCD protection he should have also rewired the lights, as the wiring had been re-designed and now the lights needed and earth.

    It was around 2018 before rest of house was rewired, and the electrician doing the work ran off into the Welsh hills, I had to do a temporary fix to keep it running, as to whom would have been reasonable I am not sure, as did get a completion certificate so suspect the LABC would be to blame if anything had gone wrong?

    But having used the LABC I know the problems, we were lucky because work being done because of mothers disability no charge, but normally the start point for any work up to a valve of £2000 in Wales is £100 plus vat, so although in theory you can change a consumer unit DIY with a £200 charge for inspectors as the LABC can charge you if they use a third party inspector, it is simply not worth the effort, in theory you should turn off the DNO isolator, in practice rarely is there a DNO isolator, so do two wrongs make a right? I know many will draw the DNO fuse, but officially you shouldn't so if the LABC inspector says do not touch, which is likely, then DNO will either need to fit an isolator or you will have to get them to draw and refit fuse, not only the DNO charge, but also without power for extended time.

    So even if in theory you can DIY a consumer unit change, in practice it is not really an option, unless you break the rules and/or law. A whole house rewire is still under £2000 in most cases so doing that as DIY may work out OK, seems crazy to put clips on an extension lead to hold it off the work top in a kitchen changes it from being an appliance to being part of the fixed wiring, so need to inform the LABC and pay £100 plus vat. I think anyone would be daft to do that, but that is the law in Wales (Not England) it was made by the English, then we got devolution, so when the English repealed the law, it was not repealed in Wales. However clearly people turn a blind eye to the law, I suspect even a scheme member would only raise a minor works and would not raise a compliance certificate.

    But they we get to how much can you break the law? So a FCU with cables to a row of sockets it with BS 7671 definition a new circuit, but I will guess no one raises a completion certificate when they do it. So a garage consumer unit is no different to a FCU but they do it seems raise a completion certificate for that.

    So who cares? with owner occupied no one unless some one injured needing doctor or hospital or killed, other wise no one knows, rented then the EICR inspector should report defects, but if a good job, how would he know no completion certificate, I misplaced the completion certificate when I came to sell the house, so contacted the LABC for a replacement, 4 months waiting list, and would need to pay by the hour for some one to look for it, seems can get insurance instead, but then found it. However since they seem unable to trace the traceable records it seems the same would apply if it did not exist.

    When I has a house buyer survey done, it included a report on the electrics, not that I wanted that, but it said there was a disused fuse box left between false ceiling and original garage ceiling in the granny flat, it was not disused.

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