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Socket outlet on a distribution circuit

Discussion in 'Electrics UK' started by equitum, 18 Jun 2021.

  1. equitum

    equitum

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    Hi I need to supply power /DB2 to a shed AKA summer house at 35M from house which is straight forward enough, however the customer also wants a twin s/o in the garden halfway. Rather than bring a cable back from DB2 (or another cable /circuit from DB1) I am considering putting the socket midway within the distribution supply cable (6mm2 swa clipped direct ) . The OCPD would be 40A. I can’t see any reason why not to but as slightly unconventional? wondering if I’ve missed anything ( I’ve taken into account VD, cable current carrying capacity, , max Zs etc and earthing considerations)
     
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  3. AndyPRK

    AndyPRK

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    you would need to have an RCD at the house end or use an RCD socket.
     
  4. equitum

    equitum

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    Yes good point because it means less selectivity on the (2) final circuits but that’s acceptable in this case and arguably better to have additional protection on the SWA than just ADS
     
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  5. EFLImpudence

    EFLImpudence

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    Normally it is not; that's why SWA is used.
     
  6. equitum

    equitum

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    Under what circumstances is additional protection of an SWA cable by a 30mA not preferable to ADS ? (Ignoring selectivity as outlined above )
     
  7. EFLImpudence

    EFLImpudence

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    It is usually not desirable for a distribution circuit to be RCD 'protected' because then all the circuits connected to it will be lost with one fault.

    One of the ways to avoid having to have an RCD on a cable is 'an earthed metallic covering' - so, conversely, if you have an RCD you don't need SWA.
     
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  8. equitum

    equitum

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    Yes agreed. Anyway back to the original question is there anything wrong with the design which would effectively be a radial socket circuit with a DB at the end feeding a 20A radial and 6A lighting cct in the outbuilding?
     
  9. JohnW2

    JohnW2

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    For what it's worth, nothing wrong that I can think of, provided that, as discussed, the socket on the distribution cable is somehow provided with RCD protection.

    Kind Regards, John
     
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  11. JohnW2

    JohnW2

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    Am I dreaming it, or did someone not fairly recently suggest that (for some reason I don't recall) an RCD socket is, strictly speaking, not an acceptable/compliant solution (despite being a common practice)??

    Kind Regards, John
     
  12. equitum

    equitum

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    Never heard that before John ? My only Thought is they meant where the cables supplying the socket are concealed in walls less than 50 mil not otherwise protected etc ?
     
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  13. JohnW2

    JohnW2

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    No, it wasn't that - the potential need for RCD protection of the cables is a separate issue.

    The suggestion came as a total surprise to me (seemingly essentially rendering RCD sockets useless!) and, as I said, I can't remember anything about the alleged reasoning/explanation - so I'll see if I can find it!

    Kind Regards, John
     
  14. JohnW2

    JohnW2

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    Found it :)

    The suggestion (from flameport) was that the Standard for RCD sockets appears to require that there is also additional upstream RCD protection (which, as he says, would essentially make nonsense of RCD sockets). He wrote:
    ... and then ...
    Kind Regards, John
     
  15. equitum

    equitum

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  16. JohnW2

    JohnW2

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    Yes, I think we discussed that ('possible oversight') at the time. However, as I've just written it seems that BS7288 may be 'the problem'.

    Kind Regards, John
     
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