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Extend new circuit from outhouse into another property with an existing supply, which is bad idea or not allowed?

Former Community Member
Former Community Member
So there is a wooden outhouse with a consumer unit of its own with RCBOs in it that gets it supply from Building A using a 10mm SWA. Building A has a 3 phase 100A power supply. 


Building B needs a new socket for some domestic appliances but has no sockets that can handle the demand in the room where it is required (dishwasher and washing machine).


Due to layout of land and location of consumer unit location for Build B (which has its own single phase existing electricity supply)  it is easier to run a SWA from the consumer unit of the wooden outhouse into Building A. So Building B is using electricity supply of Building A through the consumer unit of wooden outhouse. 


I know there are some concerns about earth bonding potential differences but what options do I have? Can I just get electricity supply from the outhouse to Building B and extend and use the earth of sockets already in Building B? 


Is something I am doing here not allowed?
  • 0
    FaeLLe:
    Chris Pearson:

    If building B is the house, I am curious to know why building A has a 3-phase supply.


    A few years ago Building A needed more power and since it has a seperate physical address the DNO put in a seperate 3 phase power supply.




    And a separate physical address is exactly what? I don't want to be nosey in this sort of forum, but the whole situation seems odd. It isn't a typical house with outbuildings.


  • 0
    AJJewsbury:

    I have copied the graphs though:

    >

    >

       - Andy.


    For interest, that set of graphs also appears as Figure 3.1 in the latest (4th) edition of the IET Electrical Installation Design Guide.

    And below it is a set of curves giving average winter weekday demand for a domestic household varying with number of occupants from 1 to 5.


  • 0
    I've identified the article - it was from the Spring 2002 (gulp!) Wiring Matters - which unfortunately I can't seem to find on-line at the moment Frowning2.

    Thank you.  My collection of pdfs goes back only to 2005.  They did nicer graphics in the old days. 

    It looks reasonable for its time. The drive for energy efficiency since 2002 has probably made a difference for the newer models. My dishwasher, for example, claims the 'standard' program to use a total of 11 L and 0.9 kWh for the entire 3h wash, and my preferred hardest-possible program is 19 L and 1.5 kWh. The washing machine claims around 0.5 kWh per wash on the standard (30 degC) setting that we normally use. Both of these are below half of what the charts claim, probably mainly because they now take so little water and avoid heating except for a few parts in the cycle (though perhaps comparing 30 and 60 degC washes is unfair).  The consumption became less than half as much when changing the 2004 washing machine in 2019. 

    So - even shorter durations of the high power would be expected in a modern machine. 


    The recent point about different addresses does add to the idea that it would be good to avoid mixing electrical supplies or making one 'address' depend on the other, e.g. if a property might be sold separately.  Is there good evidence from measurements to show that these few new loads would be too much if put on a separate circuit from the building's own supply?  Does the DNO refuse to increase the 60A?
  • Former Community Member
    0 Former Community Member
    Chris Pearson:
    FaeLLe:
    Chris Pearson:

    If building B is the house, I am curious to know why building A has a 3-phase supply.


    A few years ago Building A needed more power and since it has a seperate physical address the DNO put in a seperate 3 phase power supply.




    And a separate physical address is exactly what? I don't want to be nosey in this sort of forum, but the whole situation seems odd. It isn't a typical house with outbuildings.




    If there are two habitable buildings on a plot of land you can approach your council to request a seperate physical address (for vanity reasons or others).


  • Former Community Member
    0 Former Community Member
    davezawadi (David Stone):

    There were several overlaps in posting there, and I will go a bit further. Alcomax is right, we need simplicity. It sounds to me as if you need to get the 3 phase supply to the main house even if you need a trench which may not be as difficult as you assume. The options are to get the DNO to supply 3 phases to the house in place of the existing single phase (not ruinously expensive if you get someone with a digger to do the trenches) or to run this other cable which you say may be difficult but still only digging and careful threading under the tree roots. The new cable length needs to be considered too, and the new DNO supply may be easier than other options. I assume that the supply cable is underground, if overhead it is quite simple and cheap. You will find that most contractors will give you high prices for this kind of job, and probably suggest a lot of additional works are necessary to do the job at all. Most will run away from the two supplies problem I outlined earlier. I would expect the 10mm cable would run your new laundry fine, with satisfactory volt drop unless very long, in which case it is not the best place to put the laundry! The NICEIC is not the only contractor body, and not in any way any kind of requirement, so you can probably find a local electrician who may well be better and more reasonable to properly help you. Any questions may be asked here for solution from him or you.


    Regards

    David CEng etc.


    Not so easy David, they have the biggest oak tree in the town between the two buildings that is protected by a TPO.

    Pre-planning advise has said the council will only allow digging a trench if it is 25 meters under the soil or a semi circle with a circumference of 20 meters to avoid root disturbance. That too with strict limits on vibration created and speed of boring machines!


    Cost of project including surveys, specialist equipment and arobrists was around £30k....


  • Former Community Member
    0 Former Community Member
    So we did an "Earth continuity test" with the earth of the "power supply from the outhouse" and the earth from "the existing supply" in the building (using the gas and water pipes in the existing building).


    It seems like the earth continuity test passed and the earth of both the power supplies (outhouse and building) is bonded with the gas and water pipes of the main house. So the electrician inffered that the earthing systems of both buildings are connected?


    It is possible that the two PME earth systems are supplied by the same cable laid on the street and possible served by the same rods (or the earth is connected at the substation which is less than 50m from thouse).


    In light of this would it be safe to run a new circuit from the outhouse to the main house?


    Thanks!
  • 0
    It seems like the earth continuity test passed and the earth of both the power supplies (outhouse and building) is bonded with the gas and water pipes of the main house. So the electrician inffered that the earthing systems of both buildings are connected? It is possible that the two PME earth systems are supplied by the same cable laid on the street and possible served by the same rods (or the earth is connected at the substation which is less than 50m from thouse). In light of this would it be safe to run a new circuit from the outhouse to the main house?

    I don't see that that helps much. The continuity might be just down to the bonding of a metallic water or gas pipe - which might be replaced by plastic or have an insulating insert installed next week, or if the DNO's supplies do happen to to have a common N/PEN today, they might not next month or next year when the DNO upgrade the substation or tweak the layout of the distribution cables or re-configure a link box. Nobody will be able to make you any guarantees on that score - so you won't be able to take any precautions against the removal of such a link (to generalize one of the regs requirements). I think you'd still have to treat them as two separate supplies.


        -  Andy.

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