Upgrading the main fuse

Discussion in 'Electricians' Talk' started by Fabien, Sep 17, 2021.

  1. Fabien

    Fabien New Member

    Hi all, I'm new here and would be thankful for some advice...

    I'm thinking about installing a heat pump.
    Our house main fuse is a 64A one, and I'm told the pump would at max take 24 A.
    So I'm thinking about upgrading our main fuse.

    I'm thinking of asking for 100A to give ourselves some headroom, but 80A might also do.
    Power network asks about the meter tails...

    Would you guys be able to see from the photo if these tails are 16 or 25mm2? (I'm told they need to be 25 for 100A).

    The fuse board has a main circuit breaker of 100A so the rest of the setup looks OK?

    Are there any downside to getting a larger main fuse than what is strictly needed?

    Thank you very much in advance for your help!

    IMG_2779 copy.jpeg IMG_2781 copy.jpeg
     
  2. Coloumb

    Coloumb Screwfix Select

    You would really need to call the rec and get them to pull the fuse, until you eyeball it it could be anything regardless of what the stickers say. What do the other tails from the henly block supply?
     
  3. The Happy Builder

    The Happy Builder Screwfix Select

    What about the other consumer unit?
     
  4. Fabien

    Fabien New Member

    Thanks IMG_2782.jpeg !
    The other unit was added when the previous owner extended the house. Nothing much there, a few sockets / lamps, and towel rack / heat mat / jacuzzi.
     
  5. rogerk101

    rogerk101 Screwfix Select

    For the £10 or so that new 25mm2 tails would cost, I don't see the relevance of the electricity supply company's question ... as in, if it's already 25mm2 they they don't need to change them and if it's 16mm2 they do ... for the hefty price of £10!

    FWIW, upgrading your tails will seem like a walk in the park compared with the price of the heat pump. Mine cost me £12k.
     
  6. Fabien

    Fabien New Member

    Rogerk101:
    Apparently it’s a responsibility thing: the grid utility company is responsible for the entre cable and the fuse, but the meter and tails to it are my electricity companykss responsibility, while tails after the meter and fuse board etc are mine.
    So each is only willing to work on their own thing.
     
    rogerk101 likes this.
  7. Ind spark

    Ind spark Active Member

    The double insulated tails look 25mm.

    The single insulated tails could be 16mm, hard to tell, but they need replacing anyway.
     
  8. The Happy Builder

    The Happy Builder Screwfix Select

    The largest fuse that can be fitted in that DNO fuse holder is 80 amps, it says that on the side of it, so having a 100 amp supply requires a complete upgrade by the DNO with the fuse holder being replaced and possibly the incoming cable. You could be in for a few grand to do that.

    It’s also time you had a nice new consumer unit as well to replace that Siemens CU with Hager MCBs in it that lacks RCD protection, you could possibly install the heat pump onto the second CU, but it only has a 63 amp RCD main switch which is probably a Type AC which potentially creates issues, so to be honest you really need a new CU.
     

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