Supply to Outbuilding

Discussion in 'Electricians' Talk' started by Parttimechippy, Jun 13, 2018.

  1. Parttimechippy

    Parttimechippy New Member

    Hi Guys,
    Need advice on power supply to outbuilding which I'm planning to build shortly before building an extension and loft conversion on main house (inc full re-wire.)

    How do I go about calculating what I will need in terms of cable size and presumably a small secondary consumer unit? what about earth?

    The building will be around 30m from house, 40m from consumer unit.
    We would like to 'camp' in the outbuilding so we are out of the house and still onsite for the build which will mean a toilet and maybe some kind of water heating (presuming any domestic electric shower is a no go - maybe a 2kw water heater - not expecting anything other than a trickle for a shower) plus 1 or 2 electric heaters. And of course lighting and sockets.

    Outbuilding will be timber frame, fully insulated (50mm celotex floor, 50mm celotex +100mm rockwool walls & ceiling) and just under 30sqm footprint. I'll be digging a trench to connect to mains drainage and will dig a smaller trench within this to 750mm+ for a water pipe below frost level. somewhere above this in the trench will go a power cable and outdoor cat6 (recommended distances?)

    From a quick search cable cost for 40m is;
    10mm - £3pm = £120
    16mm - £5pm = £200
    25mm - £7pm = £280

    So in my eyes, thats no big deal just get what I need. As I said, temporary living accommodation, anti-frost heating, a small water heater if possible and then in the future, maybe a carpentry workshop or maybe a man cave with guest accommodation.

    We have planning approved, building control appointed and an electrician lined up but I'm a belt and braces kind of guy and would like to cover this myself.
    Any advice welcome! Let me know if you need a list of appliances that might be used?
  2. Dr Bodgit

    Dr Bodgit Well-Known Member

    Ask your electrician. Seriously. He will need to sign off the design installation and testing.
  3. JP.

    JP. Screwfix Select

    Can you not liaise with the electrician Part? He will do all appropriate calculations and then come up with a cable csa. Under the sparks supervion you will be able to dig the trench etc etc, and then put cable in said, and then after the sparks approves you will be able to back fill etc..also you can drill holes through wall and stuff.
    Dr Bodgit likes this.
  4. Parttimechippy

    Parttimechippy New Member

    Yep and I will be but wanted to get a 2nd opinion
  5. JP.

    JP. Screwfix Select

    I think I would use brick and block construction for the out building tbqh.
  6. robertpstubbs

    robertpstubbs Active Member

    Have you recently changed name?
  7. Parttimechippy

    Parttimechippy New Member

    no name change for me. And I can't build in brick and block, I can build in timber. for £0 labour.
  8. Parttimechippy

    Parttimechippy New Member

    Attached is the planned trench,

    but my questions are more around whats needed on the electrical side. how is it calculated as for load / losses for distance etc

    and has anyone had experience with heating and water heating for outbuildings.


    Attached Files:

  9. robertpstubbs

    robertpstubbs Active Member

    I'll have some of that £0 labour.
    Parttimechippy likes this.
  10. JP.

    JP. Screwfix Select

    The 16mm swa cable is an excellent choice.
  11. Peterdevon

    Peterdevon Active Member

    10mm will do 14kw at 40m
  12. Bazza

    Bazza Well-Known Member

    The load/cable calcs should be done by your electrician. As said above, he/she will have to CERTIFY that he/she has done the DESIGN, TESTING and INSTALLATION of the electrics.
    Dr Bodgit likes this.
  13. Bob Rathbone

    Bob Rathbone Well-Known Member

    I have multiple outbuildings at my house and the supply was installed to a small outbuilding before the house was built. My solution was to run a ring in 16mm SWA with isolators on each leg to CCU's at strategic points. It works very well, little VD and very reliable. 16mm SWA to your temporary home should be large enough, fit a small electric shower and some heating, a 60A breaker on the 16mm supply will protect the cable adequately.
  14. Dr Bodgit

    Dr Bodgit Well-Known Member

  15. Bazza

    Bazza Well-Known Member

  16. Mr Rusty

    Mr Rusty Well-Known Member

    Have a look at SIPs. You can but them online and they seem a great way of building an insulated timber frame building. I'm plotting and scheming one at the moment.
  17. Parttimechippy

    Parttimechippy New Member

    Yep I've got a sparks, he's starting on the house in a couple of weeks after a holiday. just wanted to get an idea myself of what would be needed. Don't want to bother a 2nd sparky for a quote as I know who I will be using.

    I'll get him to do all the calcs. Just wondered if there some general rule of thumb for consumption, distance and what I need to consider when listing my requirements.

    As you all says its all under planning and B/C so will be done properly. Just trying to get ahead of the game and price it all up.

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