Splitting supply to two consumer units after meter

Discussion in 'Electricians' Talk' started by Nitch1, Jun 21, 2021.

  1. Nitch1

    Nitch1 New Member

    Hi all,

    My consumer unit is currently connected directly to a double isolator which is fed through 25sqmm meter tails from the network, through a 60A fuse and the meter.
    I'd like to add another consumer unit for an extension, then have the network come and change the fuse to 100A.
    My plan is to do the following:
    1. Wire the isolator to a connector block
    2. From the connector block, pull two pairs of meter tails to two DIN enclosures, each will contain a 50A MCB for the live, neutral will go uninterrupted. The consumer units will then connect to the enclosures, earth will be wired directly to the existing connection.

    Any comments? Will this satisfy the network for the upgrading of the fuse?

    Many thanks
  2. jonathanc

    jonathanc Screwfix Select

    why do you need 100A supply?

    who is connecting up the second CU?
  3. Nitch1

    Nitch1 New Member

    The extension will have an electric shower in it, therefore more amperage is needed and I can't just connect it to the existing CU.
    The second CU will be done by an electrician.
  4. jonathanc

    jonathanc Screwfix Select

    leave it to the electrician to split the tails to the second CU. an electric shower isnt a reason to upgrade the main cutout
  5. Nitch1

    Nitch1 New Member

    Thank you, but I didn't ask who should do it, but about the soundness of the plan.
    An electrician will do all the work, however it is my experience that when I educate myself in advance and come prepared, tradesmen provide significantly better results.
    The tails from the isolator to the current CU run in the wall and are too thin to deal with the current of a cooker, heat pump and the shower running at the same time. The conduit they are in won't accommodate larger tails. Furthermore, the current CU is nearly fully populated.
    It is therefore simpler to have a separate feed for the extension.
  6. jonathanc

    jonathanc Screwfix Select

    What size are the meter tails in f you think they are too small?

    in any event I’m still not convinced you need to upgrade the cutout.

    A new cu with split tails is one approach but depending on the condition of the existing cu and tail you may prefer to upgrade that.

    Best to get your electrician appointed now so you can discuss with them. Get a couple around to quote?
  7. Nitch1

    Nitch1 New Member

    The ones running in the conduit (and in walls) from the isolator to the existing CU are 10sqmm. Not sure if they are rated 70 or 90 degrees, but either way that won't suffice as at base case scenario they can carry 75A before taking into account the conduit factor (bends and length).
    The existing CU is fairly new (5 years since construction) and just passed an inspection, absolutely doesn't require replacement.
    I will get my electrician in here, but as I wrote, I'd like to come prepared. Obviously you insist on answering questions not asked...
  8. Comlec

    Comlec Screwfix Select

    Let the electrician do the design after all it their signature that goes on the certificate.
    jonathanc likes this.
  9. jonathanc

    jonathanc Screwfix Select

    who fits a new CU onto 10mm tails without upgrading them???
  10. Nitch1

    Nitch1 New Member

    The same idiot who puts two flats and the communal areas on a single 3 phases meter with one MPRN. Took me a year and a half to sort that without being disconnected from power for 6 weeks as the network suggested.
    Mind you this wasn't an upgrade, new construction.
  11. jonathanc

    jonathanc Screwfix Select

    oh dear.... anyway

    without seeing your set up its hard to be certain but option 1) retain the 60A cutout and split the tails in henley blocks to new CU.

    option 2) upgrade the tails to existing CU and upgrade the cutout , split tails as above

    option 3) keep the existing tails and put 60A switch fuse on them ( to protect the 10mm2 tails to the existing CU), upgrade cutout and henley to split tails

    you may find that if you apply diversity, (i.e. you wont have the shower, heat pump and oven all on at once) upgrading the cutout isn't needed. (calcs needed)

    these are all ideas that your electrician may come up with. they wont use 50A mcb set up though
  12. Nitch1

    Nitch1 New Member

    Many thanks jonathanc, the switch fuse is what I was missing and is perfect to restrict the current to each of the CUs so the main fuse can be upgraded.
    Upgrading the tails is an unlikely option given the size of the conduit.
    Per the application of diversity, I'm afraid I'm married to an American, suggesting such a travesty will result in a major adverse effect on our marriage :D

    I'll run this by my electrician and we'll get going. Cheers
  13. Nitch1

    Nitch1 New Member

    BTW, here is are the current isolators, 25sqmm in, 10sqmm out and into conduit.

    Attached Files:

  14. jonathanc

    jonathanc Screwfix Select

    that was done on a price.... there's no way you could pull in larger SWA to your original CU???
  15. Nitch1

    Nitch1 New Member

    Do you mean pulling the SWA in the conduit or through another route?
    The latter is possible but not really preferred, the former brings in the question of unknown kinks on the way before even thinking about conduit factor.
  16. The Happy Builder

    The Happy Builder Screwfix Select

    Your electrical installation is a disgrace, personally as an electrician I would avoid getting involved with it.

    It’s actually bad enough to be disconnected by the DNO if you get them to do a site visit.

    The SWA needs terminating into a fused switch with new tails connecting it to the DNO isolation switch.
  17. Nitch1

    Nitch1 New Member

    Happy builder, is your issue just with the gauge of the tails or something else? Just curious
  18. The Happy Builder

    The Happy Builder Screwfix Select

    It’s unacceptable because:

    1. The suppliers fuse is being used to protect the SWA, which is not suitable for use as meter tails, so does not comply with the suppliers regulations.
    2. Presumably the SWA is more than three metres in length, which is more than the DNO allows, so does not comply with the suppliers regulations.
    3. The SWA is stripped back leaving single insulated cables exposed to touch, which does not comply with The Wiring Regulations.
    4. The SWA hasn’t been terminated correctly, which does not comply with The Wiring Regulations.
    It’s not going to kill you if you touch it, but it rough and unacceptable.
  19. The Happy Builder

    The Happy Builder Screwfix Select

    The cables have to be rated at 70 degrees even if it’s 90 degree cable, because the terminals can only run at 70 degrees.

    This installation should not have “passed” an inspection.
  20. The Happy Builder

    The Happy Builder Screwfix Select

    And that bit about “conduit factors” is utter tosh.

    You need to find a decent electrician and don’t try to tell him or her what to do, best of luck.

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