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Self-Build - Boundary Box help...

Discussion in 'Electrics UK' started by christianbeccy, 17 Oct 2021.

  1. christianbeccy

    christianbeccy

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    We're in the early stages of a self-build. We plan a 3ph connection, which will have to be to a Boundary Box at 35m from the base of the pole. This is still some way from the house, probably around 50m. Is this a concern?

    There is a closer pole that is probably shortens the distance between the Boundary Box and the house to about 20m, but it's £2000 more to connect here.

    Any help is appreciated.
     
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  3. flameport

    flameport

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    Further away = much larger cable required and longer trench, both of which will cost more.
    Nearer = smaller cheaper cable and shorter trench, but the connection cost is more.

    All depends on the relative costs of the two options.
     
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  4. christianbeccy

    christianbeccy

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    OK great, but with cost aside is the longer run detrimental in any other way?
     
  5. ericmark

    ericmark

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    The DNO are permitted to supply at a voltage of between 207 and 253 volts, and your permitted 5% on power and 3% on lighting, so it is the lighting which is real limit. My calculator only goes to 16 mm² so at 100 amp so will not work it out but would guess looking at least at 25 mm² so for 5 core looking at £20 per meter so 35 m = £700 and 50 m = £1000 however may need to go to 35 mm² which means £25 per meter so £1250 so likely cheaper for you to run cable not DNO.

    But although the likes of CEF may publish price of cable, in real terms it is negotiable, so not so easy to calculate. And not included price to dig trench.
     
  6. JohnW2

    JohnW2

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    Not that I can think of - if properly designed, the longer the run, the larger the cable will one use so as to get the voltage drop (and 'wasted energy' cost) down to the same level, so it shouldn't make any difference, other than in terms of cost (of both cable and its installation).

    Kind Regards, John
     
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  7. winston1

    winston1

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    You will not pay for the wasted energy though as the meter is at your end of the cable.
     
  8. JohnW2

    JohnW2

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    That's true - but, as far as 'the planet' is concerned, it is still a cost in terms of wasted energy (unless you can think of some benefit which derives from 'heating the soil').

    In any event, consumers in general will ultimately pay (in £s) for un-metered energy wasted in the distribution network, since the price they pay for metered electricity will take into account the energy for which DNOs and suppliers pay which is 'expended' upstream of consumers' meters.
     
  9. Harry Bloomfield

    Harry Bloomfield

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    I once saw a figure of 10 to 30% for the the overall network - Have you seen a different figure?
     
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  11. SUNRAY

    SUNRAY

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    One only has to look at the efficiency of the network transformers of 1% to 2% and the older versions may be nearer 5% to see some huge losses.
     
  12. SUNRAY

    SUNRAY

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    I doo of course mean 99% to 98% and 95%.
     
  13. Harry Bloomfield

    Harry Bloomfield

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    There is a lot more to the network, before the power gets to where it is used, than just the transformer and losses are additive.
     
  14. JohnW2

    JohnW2

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    I don't recall having ever seen 'a figure'.

    However, it's obvious that those who do the generating the electricity will expect to be paid for all the electricity that they generate and fee to the grid, regardless of whether that energy is put to useful use by an end-consumer or is dissipated ('wasted') somewhere between the generator and the end-consumer - and that cost "of everything generated" will be passed on by suppliers to the consumers.

    My blind guess would be that an 'appreciable proportion' of the energy would not get to consumers, so I would not argue with the ballpark you mention - although I would probably have guessed nearer to 10% than 30%.

    Kind Regards, John
     
  15. Harry Bloomfield

    Harry Bloomfield

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    It will of course vary with the load - transformers, up to a point, become more efficient as their load increases, where as cable efficiency is at maximum the lighter the load.
     
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  16. SUNRAY

    SUNRAY

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    Oh yes absolutely, again one only has to look at the wire strung up on pylons and although running at a tiny % of the current in an equivalent LV network the copper losses are very much still there.


    Iassisted with installing KWh in the LV side of a customers HV network and within a few weeks they started questioning the difference of a 3-4% between the 'new meters' and the 'Suppliers meters', the Transformers were ancient.
     
  17. christianbeccy

    christianbeccy

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    That's the answer I was hoping for. Thanks!
     
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