Discussion in 'Electricians' Talk' started by rogerk101, Feb 21, 2021.

  1. rogerk101

    rogerk101 Screwfix Select

    Given that our hosts and their competitors don't seem to sell CUs prepopulated with RCBOs, I'm looking for the most cost effective way of buying, say, a decent 18 way metal CU with:
    • 100A DP mains isolator
    • SPD
    • 10 RCBOs (1 x 50A, 5 x 32A, 1 x 20A, 3 x 6A)
    • 4 blanks for future expansion
    Where would be the best place to buy something along those lines?

    Before any of the pro sparks suggest I leave this to my spark to buy, he'd rather not have to buy it himself because he is just below VAT threshold so prefers it purchases like this go through his customers' books rather than through his own.
  2. Pete Jones

    Pete Jones Active Member

    Midshires wholesalers
  3. MGW

    MGW Screwfix Select

    Got mine from Link, made an error, all the RCBO's said type B on box, but turned out to be curve B type AC.
  4. Philip Hyde

    Philip Hyde Screwfix Select

  5. The Happy Builder

    The Happy Builder Screwfix Select

    Screwfix sell all RCBO consumer units

  6. rogerk101

    rogerk101 Screwfix Select

    Thanks. Unfortunately that's only 8 RCBOs and being 12 way, there is no space for the remaining 2 RCBOs that I need and for the 20% spare capacity usually required in a new CU install.
  7. rogerk101

    rogerk101 Screwfix Select

    Philip Hyde likes this.
  8. rogerk101

    rogerk101 Screwfix Select

    They seem to sell Wylex CUs with mains isolators and SPDs but no RCBOs. :(
  9. Nomenklatura

    Nomenklatura Active Member

    But does he have no preferences?

    Sparks often do.
  10. Nomenklatura

    Nomenklatura Active Member

    I've seen that exceedingly annoying mix-up of MCB curve and RCD type as well. Makes finding devices a PITA.

    Full marks to the fools who decided to create the possibility for that confusion.

    Can you actually get type B or type F RCBOs?
  11. Bazza-spark

    Bazza-spark Screwfix Select

    I asked a similar question twice of the "experts" on Voltimum 18 months ago and still havent had an answer.
    Nomenklatura likes this.
  12. Comlec

    Comlec Screwfix Select

    I use Contactum boards from TLC-Direct. 16 Way Metal Consumer Unit - 100A Main Switch (tlc-direct.co.uk)
    Putting your requirements into my CU planner gives a 16way board with main switch, SPD, 10 RCBOs (B Curve type A), tails gland and tails = £270.69.
    rogerk101 likes this.
  13. rogerk101

    rogerk101 Screwfix Select

    Surprisingly the spark suggested BG.
    My only experience of BG was when I bought a fully populated 10 MCB dual RCD metal CU from our hosts a year ago, only to find that the MCB arrangement didn't match what they said on the box, and one of the two RCDs failed the time test when the spark that installed it came to testing it all. (This was a different spark from the one who is insisting on a new CU after a few too many C2s in an EICR he performed last week.)
  14. spinlondon

    spinlondon Screwfix Select

    Nomenklatura likes this.
  15. Nomenklatura

    Nomenklatura Active Member

    Might be better off enquiring of the sales or technical departments of major manufacturers
  16. spinlondon

    spinlondon Screwfix Select


    Thanks for your enquiry and Type B RCD’s have quite a bespoke application and, at the moment, our technical constraints do not allow the device to be compact enough to be in an 18mm modular width

    Therefore, you would need to use an mcb in conjunction with the RCD to provide this application to your circuit

    With best regards,

    Electrium Sales Limited
    Walkmill Lane
    Cannock WS11 0XE, United Kingdom
    Tel.: +44 1543 455000
    Fax: +44 1543 455001
    Nomenklatura likes this.
  17. Nomenklatura

    Nomenklatura Active Member

    I did wonder if that might be the case with Type B (and F).

    Maybe we should prepare ourselves for CUs to get a lot bigger, to allow 2-module devices. At least the opening up then of the possibility of 2-pole busbars would make wiring simpler.
  18. The Happy Builder

    The Happy Builder Screwfix Select

    Do you really need four spare ways in a consumer unit rated at 100 amps in addition to circuits with a total capacity of 248 amps?

    What size is the suppliers fuse?
  19. rogerk101

    rogerk101 Screwfix Select

    The current CU contains 10 MCBs and I'd like to replace each of them with an RCBO of the same overcurrent rating (as per the above list).
    The mains isolator takes 2 ways.
    The SPD takes 2 ways.
    That's 14 ways minimum.
    General guidance for the installation of a new consumer unit is to allow for 20% more circuits to be added; so 2 more ways required/desired in my case.
    I'd like a minimum of a 16 way CU to achieve the above.

    The main fuse is currently 100A, but the tails are 25mm2 so capable of more than 100A if ever the need arises for that ... not that that is likely. However, without spare ways what do I do if I suddenly decide I want to install a charger for an electric vehicle, or power a shed off its own circuit? I don't plan on drawing anything like 248A at the same time, but I don't know of a single house I've ever owned or worked on where all MCBs add up to be less than the maximum current rating of the RCD protecting them, or even the (usually 100A) mains isolator.

    If you are a professional spark and a customer asks you for 4 main ring circuits (upstairs sockets, downstairs sockets, kitchen sockets, annex sockets) each with their own 32A MCB, would you tell them they can't do that because they'll be exceeding their two 63A RCDs and their 100A mains isolator. I'm pretty certain every CU you have ever worked on has more current carrying capacity in the MBCs than catered for in the RCD(s) and mains isolator.
  20. MGW

    MGW Screwfix Select

    In my house the DNO fuse is 60 amp, so a 63 amp RCD would be fine even if feeding MCB's with total of 400 amp. With caravans I have seen a 10 and 6 amp MCB with idea your MCB should trip before the sites 16 amp, but with a house never seen it arranged so your trips will always fail before the DNO fuse.

    The CU type testing means 125 amp max, in real terms 100 amp, if you need more than 100 amp, then either split phase, or three phase, even with old economy 7 two independent supplies with 100 amp each, never seen a domestic with over a 100 amp DNO fuse.

    I have not seen a CU with a smaller than 100 amp isolator, the RCD may be 63A, 80A or 100A, but isolator always 100 amp, and you will not have any RCD's so that does not matter.

    As to electric vehicle, it seems to get better than type A RCBO you need more than one slot, so very likely will need some sort of RCD or DC detection built into the charging pod, so often not fed from consumer unit anyway.
    rogerk101 likes this.

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