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Power design for garden studio

Discussion in 'Electrics UK' started by FrankM45, 12 Jun 2019.

  1. FrankM45

    FrankM45

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    Am planning a garden studio build soon and interested in views and comments for planning power supply.
    Existing house is TN-S system; I'm thinking of 6mm 3 core SWA, about 20M run to studio, fed from either existing ring main in garage via a DP isolator, or spare way in CU, but the latter will be difficult to route from.
    The SWA at studio end would go to small CU with RCD, to power a number of sockets, lighting and an aircon unit. I haven't calculated the potential loading yet but it will not be above 10 -12A I would think.

    Is the TN-S ok to export or does it need an earth rod and therefore provide TT at the studio?
    Is a second RCD recommended at the garage end?
    Is feeding from the existing ring main OK if I cant utilise the spare way in CU?

    many thanks
     
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  3. Notch7

    Notch7

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    Its not good practice to have 2 RCDs inline -because there would be no discrimination. I think electricians recommend an rcd at the outbuilding end and an mcb at the CU.

    You must be asking because your electrician is away on hols at the mo (y)(y).
     
  4. John D v2.0

    John D v2.0

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    You wouldn't need a cu in the garage if it's fed off a ring.
    You would need to check voltage drop and disconnection times though at the far end of the circuit.
    Regarding exporting the supplier earth you would have to decide whether it's practical to extend the equipotential zone to include the outbuilding. Any extraneous parts? What is the floor construction?
     
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  5. FrankM45

    FrankM45

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    Thanks John D

    I was considering the CU so the supply for sockets, lighting and AC could be separated by it inside the unit. Also, there would be an RCD in the CU. I realise the overall loading on the supply is the same. The voltage drop and expected loading still to be calculated.
    There will be no extraneous parts and the floor will be concrete base with screed and probably laminate floor covering.
     
  6. chivers67

    chivers67

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  7. FrankM45

    FrankM45

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    Thanks Chivers - useful. Ive guessed the load as I'm not sure yet but at 3kw, the recommended size of (SWA) wiring is shown as 1.5mm or 2.5mm if longer length run.
    Ive noticed in the forums that most people recommend 6mm or 10mm wiring - is this overkill or a miscalculation on my part? as I said, I haven't calculated the potential load yet but it should be below 13A or thereabouts.

    Thanks
     
  8. ban-all-sheds

    ban-all-sheds

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    Neither, really, It's a form of contingency planning.

    When considered in the context of the cost of doing the work, digging the trennch, making good, the services of an electrician (which you are absolutely going to need), the cost of a larger cable is insignificant, so if your needs ever change, e.g. if you decide to take up pottery, or want a decent hot-tub, you won't need to dig it all up and do it again.

    Another option is to install a couple of ducts, one for power, and one for data.

    Do you live in England or Wales?
     
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  9. FrankM45

    FrankM45

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    no data needed so just one cable required
     
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  11. Taylortwocities

    Taylortwocities

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    If you are “tapping” it off a ring final, your maximum will be the 13amp fuse in the FCU!
    Separate switched fuse, separate from house CU. No RCD at house end. But your electrician will be telling you all that.
     
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  12. FrankM45

    FrankM45

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    Thanks TTC - yes I understand that.
     
  13. garyo

    garyo

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    As a starting point for guesstimation I'd want to be able to plug in a 3KW fan heater, plus some interesting power tools, lighting, IT stuff, so 3kw seems too low.
     
  14. ban-all-sheds

    ban-all-sheds

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    So it's notifiable then.


    Never?
     
  15. ban-all-sheds

    ban-all-sheds

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    Don't think it's a workshop.


    Apparently not.
     
  16. FrankM45

    FrankM45

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    Haven’t a clue what garyo’s post is about. I’ve no intention of plugging in a 3kw fan heater. I’ve also no intention of using power tools, interesting or not, it is not a workshop.

    I will not need data or network cabling as it’s wifi based. And yes I do know it’s notifiable.

    Current load is expected to be low.

    Thanks
     
  17. oldbutnotdead

    oldbutnotdead

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    WiFi? For recording? Entirely your decision of course, but while you're digging a trench up the garden throw a duct in for a couple of lengths of CAT5- the cost is buttons compared to the rest of the job and wired will nearly always be more stable and give better sustained high bit rates than wireless. And you might want to throw some alarm cables up the duct as well......
     
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