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Modernising a Domestic Installation - Multiple Consumer Units

John R.

I'm buying a house where the electrical installation is, for want of a better description, a complete mess!

I'm assuming that the existing supply is PME and will check and also measure earth the loop impedance when I get full access.

Currently there's one consumer unit in the downstairs entrance which is old having only fuses and no spare ways.

The plan is to start by renovating upstairs, which will involve re-insulation and will provide great access..
So I think I may as well re-wire upstairs while access is available.

I reckon that the easiest thing to do will be to install an upstairs consumer unit, and at some later time, a new downstairs one.
This will also allow for shorter final circuit cable runs so simplify installation.

Hence to my current deliberations.  I think the following is correct.

(a) The 'main distribution board' needs to house CBs only to protect the cables to the CUs.  (CUs will include RCDs whether required or not)

(b) There's no requirement to have any RCDs in the 'main distribution board'.

(c) There may be merit - or even a requirement - to include SPDs in which case these would best be in the 'main distribution board'.

Does this make sense?  Any comments appreciated.

For background: in my early career I worked as an electrical building services designer for a consultancy.  That was a a long time ago, and that work was on commercial not domestic premises.

  • in reply to John R.
    John R. said:
    If you have one, I'd quite like a recommendation for which manufacturer's products to look at, particularly for the 'main distribution board'.

    If you now want fuses, you only need a couple, but perhaps allow for a third to peel off to the garage or outbuildings.

    A TPSN switch-fuse(-disconnector) could be used. Eaton Glasgows are built like a brick dunny - they pop up pretty regularly on eBay, if price is an issue.

  • in reply to Chris Pearson

    Thanks Andy and Chris

    I did actually see the Eaton boards on eBay having seen some silly prices elsewhere.

    I was looking at DIN rail mounted fuse holders able to take up to 25sq.mm cables.

    Ideally I need to find a board that will take SPDs too.

  • in reply to John R.
    John R. said:
    I was looking at DIN rail mounted fuse holders able to take up to 25sq.mm cables.

    If it helps at all, this is the kind of thing I used: https://uk.rs-online.com/web/p/fuse-holders/1444544 (although mine had a different brand label). The way the holder opens (the front rotates down to open) means that a lot of DIN rail modular enclosures don't fit (and of course you'd be limited to steel enclosures these days for domestics). 58x22 is the size of the normal BS 88 (BS 1361 as was) "cut out" fuses - so will take 63A, 80A, 100A etc.

    Ideally I need to find a board that will take SPDs too.

    You can get "main switches" with a built in SPD (e.g. https://www.tlc-direct.co.uk/Products/WYREC2SPD.html ) - which might be useful if you were going down the Henley blocks and several separate 1-way switch fuse route.

      - Andy.

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