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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.

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  • Hi John

    Unless you have wooden floors down stairs that can be lifted to wire the ground floor sockets pretty much all of the wiring for up and down stairs is in the ground floor ceiling / first floor floor. If this is the access you are talking about you will need to at least partially rewire or install cables for down stairs at the same time. Certainly the ground floor lights will be in the ceiling.  I personally think an upstairs CU over complicates things unless this is a very large installation.

    Gary

  • in reply to aligarjon

    Downstairs floors are wooden, and so I think that cabling to sockets will be underfloor but will only know that for sure when I start to pull things apart.

    I've seen some evidence of steel conduit, so hopefully if this is in place, running replacement wires will be easy.  Probably won't be that lucky!

    It's not a huge installation, but access to the downstairs CU is problematic and I want to get to the stage where the existing cupboard contains only the distributor's equipment.  The use of two CUs is very much for convenience of doing work but I will have more circuits than is perhaps common.

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  • in reply to aligarjon

    Downstairs floors are wooden, and so I think that cabling to sockets will be underfloor but will only know that for sure when I start to pull things apart.

    I've seen some evidence of steel conduit, so hopefully if this is in place, running replacement wires will be easy.  Probably won't be that lucky!

    It's not a huge installation, but access to the downstairs CU is problematic and I want to get to the stage where the existing cupboard contains only the distributor's equipment.  The use of two CUs is very much for convenience of doing work but I will have more circuits than is perhaps common.

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