Underground supply to garage & barn

Discussion in 'Electricians' Talk' started by Robn, Jun 28, 2016.

  1. Jitender

    Jitender Screwfix Select

    Don't know much about electrics, but would have the barn on a new supply and and a the carport as sub main.

    And have annex fed off from garage.

    Is it single phase coming into house?

    Is the main supply coming in from road at A?
     
  2. Robn

    Robn New Member

    Yes its single phase main supply coming in at A, the pole is about 10m back.
    With a new supply they'd need to run it underground past the house and the garage anyway, I presume to have the electric board do that and install a new meter in the barn, etc will be much more expensive than me digging it in myself? And then I still need to run B-C to get power to the gararge....
    I guess though it wouldn't hurt to get a quote for a new supply to the barn, I wasnt considering it as I assumed it would be too expensive..
     
  3. Jitender

    Jitender Screwfix Select

    WPD.jpg A quote from WPD (2013) for moving an electric supply. I assume new installations will be more expensive.

    Can do the trenching yourself. or they charge £23/m for rough ground
    £28/ for grass.

    £11/m for cable.

    i would contact them to get a quote.
     
    Last edited: Jun 30, 2016
  4. TP&N

    TP&N Active Member

  5. Jitender

    Jitender Screwfix Select

    Did you get a quote to install a separate supply?
     
  6. JP.

    JP. Screwfix Select

    Not cheap whatever way you look at things - I would be surprised if you could get away with 1.5k tbqh. However at the end of the day if it is all done properly then costs really have to take 2nd place..a pukka job is worth its weight in gold.
     
  7. Robn

    Robn New Member

    Hi Jitender, having seen your post in the end I didnt actually get a quote, as the new supply route was going to be way more expensive - mostly due to the £11/m cable charge => £1100, connection charge in the hundreds, as opposed to 100m of 16mm SWA at <£400

    Just to update, having consulted the electrician I usually use he worked it out and said 16mm SWA will be fine for a 40A load and the voltage drop is OK too, as its underground ~15C or less, the drop is 9V which is (just) less than the 4% regs (it's 11.6V drop at higher temp above ground, from the tables)

    Seems fair enough, as a two bed with oil heating the barn load wont be over 40A.

    Cheers
    R
     
  8. JP.

    JP. Screwfix Select

    Are you sure about 16mm guv?

    Surely 25mm is indicated
     
  9. leesparkykent

    leesparkykent Well-Known Member

    3% (6.9V) for lighting and 5% (11.5V) for power are the recommended values in BS7671. Your electrician has used the correct table however its based on ~20C not ~15C as you've indicated. Also on top of the length of the distribution circuit to the barn you need to consider the length, current, installation methods of final circuit and distribution circuits fed from the barn. IMO 16mm is undersized and your electrician should go back to the drawing board. If you are just after an installation that works and is cheaper than doing it properly then crack on with the 16mm ;)
     
  10. peter palmer

    peter palmer Screwfix Select

    Most lights are LED nowadays so whats the point in sticking to 3% when the lamp electronics reduce it to 12 volts anyway.
     
  11. Lectrician

    Lectrician Screwfix Select

    Most LED fittings have input voltages with ranges like 100-250v these days!
     
  12. Robn

    Robn New Member

    Hi Lee
    Sorry for the vagueness in the figures I was just quoting from my head, temperature/percentages etc.
    Believe me, I'm not the sort of person that likes to cut corners or not do something properly, but I'd have to make a point here. If what my electrician has recommended is inside the regs (and let's face it, there's plenty of wriggle room in there - this cable isnt going to melt/catch fire underground at 100A let alone 40A ) I can't see why you think 16mm is undersized. Sorry if I'm "just after an installation that works" - but who isn't? And it's binary - it works for the quoted load. If your idea of 'properly' is to over-spec the cable (and that results in a couple of hundred ££ extra for this job) - then surely you are doing your customers a disservice and causing unnecessary expense, for the dubious comfort blanket of 'a proper job'. I'm not a sparky, I'm an engineer and over-design is a problem in my field - extra materials, weight, expense, etc. I've been taught to trim to spec, and I don't see the need to over-design in this case (or any other).
    That said, I'm not trying to have an argument with you (and I am grateful for your input on this thread). Just don't see how something within the spec and within the regs can be not 'doing it properly'. And a bit of devil's advocate :p
     

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