Single RCBO in CU

Discussion in 'Electricians' Talk' started by rogerk101, Dec 22, 2020.

  1. rogerk101

    rogerk101 Screwfix Select

    Hi All
    I have a regular old style Hager CU with a single RCD. Roughly half the circuits are RCD protected and the other half are not. I'd like to put my cooker circuit onto an RCBO and was wondering what an acceptable method would be for connecting the mains, cooker and RCBO neutrals. I obviously can't connect them on the RCD neutral bus bar, and not can they go on the nonRCD neutral bus bar, so they will have to be connected separately.
    Would a wago-style connector block be OK?
    Would the connector block need to be attached to the CU with a proper mounting?
    Are there any regulations about this?
    Anyone ever done this before?
  2. seneca

    seneca Screwfix Select

    The cooker neutral will go into the top of the rcbo won't it Roger, so that only leaves the rcbo neutral so i'd imagine there will be enough room at the load side of the isolator switch for that?
  3. Philip Hyde

    Philip Hyde Screwfix Select

    Fly lead would go in Non Rcd N Bar and Circuit N would go into N terminal on RCBO

    Attached Files:

    seneca likes this.
  4. Bazza

    Bazza Screwfix Select

    @rogerk101 its a new circuit, so notifiable work. Given the nature of your queries, I guess you aren’t able to self notify, or to certify this.
    You need a registered electrician to do this for you.
  5. Philip Hyde

    Philip Hyde Screwfix Select

    RogerK101 is it a new circuit or are you simple wanting to swap MCB for RCBO on existing cooker circuit?
  6. Sparkielev

    Sparkielev Screwfix Select

    You seem to be a knowledgeable guy am surprised you dont this
  7. Bazza

    Bazza Screwfix Select


    my thoughts are: why do you need to protect this particular circuit with an RCBO?
  8. rogerk101

    rogerk101 Screwfix Select

    Thanks for the replies and the guidance.
    It's not a new circuit ... just decided that I'd rather have the cooker protected and felt it better to do it with an RCBO than moving it across from the nonRCD side to the RCD side.
  9. MGW

    MGW Screwfix Select

    I really don't understand the question, why can"t the RCBO fly lead go to the non RCD neutral bus bar? I have mixed MCB with RCBO for years, two small problems, in some boards they will not physically fit, and in some boards the on for the MCB was reverse direction to RCBO but that was a distribution board not type tested consumer unit.

    As to NEW circuit that has always been a problem to define, I would have said fitting a FCU was generating a new circuit, but it seems this is not seen as a new circuit. The phrase is let the courts decide, and it seems unlikely there will ever be a court case to decide.
  10. CeSparky1

    CeSparky1 Active Member

    Its probably not really a new circuit, if your changing from an mcb to and rcbo then it would be an alteration...

    Having said that there is no point in having an rcbo if you dont then test the circuit and rcbo to make sure that it will function correctly. Do you have a multi function tester? I would seriously suggest if your going to open up your consumer unit given your question then I would highly recommend getting in a qualified electrician, it really should not cost that much. I charge £35 per hour, min one hour, even with testing will take less than an hour if you have everything ready to go and easy access. I know most electricians have a minimum charge of £50 or £60 but even so its not exactly expensive.
    Bazza likes this.
  11. MGW

    MGW Screwfix Select

    You can get a tester to check if RCD/RCBO works cheap enough, found one for £9 plug in with test button, even shows the L-N and L-E voltage, but to test it trips in 40 mS it jumps to around £250, personally since the 40 mS is only valid when load has no DC so even when it passes it still may not trip if some equipment goes faulty causing a DC leakage, I would say the £9 tester is good enough, if it trips, even if not in 40 mS then in the main your OK until next you have an EICR done.

    Clearly electricians must check it trips in 40 mS but as a DIY guy I would not be that worried. I was a little worried when I found all my RCBO's in spite of saying in big letters on box type B, are actually type AC, I ordered replacements for socket circuits type B but after 9 months still have not come, so cancelled order. I think the chance of a fault causing DC and RCBO to freeze and also a fault which needs the RCBO to trip is rather remote.

    If I was using a RCD then would be a little more worried, as covers many circuits, but for RCBO think the chance of two faults one freezing the unit then other needing it to trip at the same time is rather remote.

    I am surprised the RCD testers don't have a 6 mA DC injection to test if type A will still trip with DC.

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