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Residential 3 Phase Supply to Single / 3 Phase

Discussion in 'Electrics UK' started by sparkypenguin, 18 Sep 2021.

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  1. sparkypenguin

    sparkypenguin

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    Hi all,

    I am currently in the process of building a self build and have a few questions about the distribution of power.
    I am not an electrician but do have a basic understanding of electrics.
    Also to confirm I will not be fitting this as I will be employing a qualified electrician when the time comes.

    I decided to go 3 phase for my incoming supply to allow for electric car charging etc and I am getting a 3 phase smart meter installed next week.
    I have been reading various posts and articles etc and I believe that the best way to go would be to use a 3 phase split distribution board as follows:-

    upload_2021-9-18_11-8-33.png

    Thus allowing me to use a combination of single phase and 3 phase equipment.
    Does this look acceptable and should I be adding a 4 pole isolator switch?

    Any help much appreciated.
    Mark.
     
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  3. chivers67

    chivers67

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    I'd just use a three phase Schneider board and use RCBO's or MCBs as appropriate. you can use 3 phase or single phase still? How many circuits and how big is the property?
     
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  4. flameport

    flameport

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    No, it's a total shambles.

    A standard 3 phase board and RCBOs as above.

    Install a foundation earth electrode while you still have the opportunity.
     
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  5. sparkypenguin

    sparkypenguin

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    TBH I thought that was a standard 3 phase board just with the incoming split into 2 sections, 1 for 3 phase and 1 for single phase?
    House will have approx. 36 circuits in total.

    Is there anything specific that makes it a total shambles?

    Will do.
     
  6. chivers67

    chivers67

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    How big is this property? For instance it might be best served with more than one DB if it's more than two floors - perhaps a top floor with it's own board fed by an SWA cable or something.
     
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  7. flameport

    flameport

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    The whole concept of it being split into two sections is entirely pointless and unnecessary.
    Upfront RCDs which will take out most of the circuits when there is a fault - also undesirable and unnecessary.
    If such a thing was actually wanted, it would have to be custom manufactured at substantial cost.
     
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  8. sparkypenguin

    sparkypenguin

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    It's 2.5 floors and your suggestion is a good idea (y) or would have been a few months ago but I've already had most of the cables installed and they all terminate in the garage (n).

    Now that you've pointed it out I do see what you mean. (y)

    Are Schneider boards good value for money and do I have to use the same make of MCB's etc?

    I have also been reading about how to identify and split the single phases over the house.
    Some suggest that you should identify the different phases by sleeving the live with the phase colour whilst others say live should always be brown?
    And some suggest that you should keep the different single phases away from each other, i.e. P1 ground floor, P2 first floor etc, whilst others say that it makes no difference?
     
  9. flameport

    flameport

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    Schneider make decent equipment. Other manufacturers are available.
    Whatever is chosen, it must all be from the same manufacturer. Schneider RCBOs in a Schneider board. Hager RCBOs in a Hager board.
    They must also be of the correct type for use in that specific 3 phase board - some manufacturers make different incompatible ranges, and some devices designed for use in a single phase consumer unit are not suitable for use in a 3 phase board even though they look similar.

    For single phase circuits it's not necessary to identify which phase is in use. Could be done if desired, black and grey sleeving is available. So are number and letter wire markers.
    Not necessary to keep phases separate per floor, per room or anything else.

    Generally recommended to split the total load of the property across all 3 phases, and not have any single type of circuit on a single phase. As an example, if there were 6 lighting circuits it would be sensible to have 2 on each of the 3 phases.
     
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  11. Adam_151

    Adam_151

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    I think you've picked up something unintential from the picture; while all the three phase cirucits are on the bottom section and the single phase circuits on the top, thats not an integral part of the arrangement shown, you could have both sections with a mix of tpn and spn. But as flameport states, its a poor arrangement, its the commericial equivelent of a domestic split RCD board (which has compromises that only make sense for small domestic properties) thus, you won't find anything like the picture on the shelf, but many manufacturers could provide a custom solution in line with the picture using their modular parts, and they probably exist as line numbers in the catalogue that are rarely ordered and are built to order....

    You'd be limiting yourself if you want to add EV charging etc, as you want to avoid sharing the RCD with anything else, and that arrangement doesn't permit that, plus in a larger property as this sounds like it is, the dual RCD arrangement is likely to be subject to nuisence tripping.

    The RCBO route is sensible to go for, but if cost is important, then you can save money by being careful what brand you go for, Schneider boards are very good kit, but both the boards and the RCBOs are on the dear side, Acti9 (and now the Acti9 Isobar P sub range of this ) is generally whats specified on high end commericial jobs (This was what was previously known as Merlin Gerin), I beleive the Schneider iKQ range is slightly better on price (previously Square D), Hager is good quality still but is more reasonably priced, I wouldn't recommend you go for any of the low end boards as in 15 years time when you need an extra RCBO you might not be able to find them
     
  12. sparkypenguin

    sparkypenguin

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    Thanks for clarifying (y)

    Does it matter if the 3 phases are balanced?
    I have read that it does not really matter as it's just like having 3 different houses one on each phase, however I have also read that it could lead to a high and dangerous neutral current?
    If I was drawing the full 18KW on one phase and nothing on the others would this matter?
    Do I need to fit some form of Neutral overload protection?
     
  13. sparkypenguin

    sparkypenguin

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    So something like this would be suitable?
    upload_2021-9-18_18-27-54.png .
    Using a Hager JK112BG Invicta3 Metal 12 Way Standard Type B Three Phase TPN Distribution Board With Glazed Door Without Incomer 125A.
    and just wire as a normal CU using all 3 phases for 3 phase stuff and splitting the single phase requirements over the 3 phases equally?
    Would that be OK for single phase and/or 3 phase EV charging?
     
    Last edited: 18 Sep 2021
  14. Adam_151

    Adam_151

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    Thats just an standard TPN board you have shown, The size you pick depends on how many cirucits, obviously a 12Way board will give you 12 TPN ways, or 36(3x12) SP ways, or any combination in between.Normal to leav at least 20% spare ways.
    You'll need RCBOs on most if not all of you SPN circuits, TPN cirucits may or may not need RCD protection, TP rcbos are an rare/unusual thing, so if you needed RCD protetcion to a three phase circuit, then stick a service centre on the top or bottom of the board and run the cirucit through 4 pole RCD in there. Or design so that you dont need an RCD at the board end.

    You'd of course want the incommer as well, thats a rookie mistake to make to order board without the incommer!

    Who is in charge of designing/installing the installation, because it sounds like you want to order a board without really understanding what you actually need.......
     
    Last edited: 19 Sep 2021
  15. winston1

    winston1

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    er no. If the neutral was disconnected by a breaker or fuse the line voltages could drift all over the place up to 415 volts.
     
  16. 333rocky333

    333rocky333

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    Neutral overload protection shuts off the supply, rather than disconnect the Neutral, I dont recall it being needed for the average install
     
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  17. 333rocky333

    333rocky333

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    Your drawing appears to show a TT system, if so i believe the incomer needs to switch all 4 poles including the Neutral
     
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