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Single phase sub-main

GA

Evening, I'm seeking some advise pls. I have a 4core 25mm2 SWA and was going to use this for two single phase submains running from and to a common point, where the circuits will then go into separate consumer units. limited loads a garage and stable. The cable will have DP isolation and RCD protection on each circuit (2cores L+N per sub main) at the supply point. I'm also looking to run a separate earth cable of 25mm2 which would be common to both circuits and armouring of the SWA cable is also earthed and common. My question is I believe this to be complaint with 17th Ed; As I can't see anything saying its not. Second question, could I common the neutral for both submains and therefore use the fourth conductor in the SWA as an earth which would save installing the separate earth cable? Again, I can't see anything incorrect as limited loads to a couple of sockets and a few lights.  thanks for assistance. GA

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    QUOTE: “(b) the TT system is derived from a TN system, and unfortunately shares extraneous-conductive-parts with that system. Again, can't rely on that for protection against electric shock … but this time we definitely need to size our cpc's in a similar manner to TN systems for protection against overcurrent (earth fault current). Again, the RCD is not an overcurrent protective device according to BS 7671, it requires back-up of a suitable overcurrent protective device, and the cpc sized accordingly.”

    But if the stable has no extraneous-conductive-parts and is of wooden construction, perhaps with a blue plastic water pipe only, that puts a different complexion on things.

    Z.
     

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  • 0

    QUOTE: “(b) the TT system is derived from a TN system, and unfortunately shares extraneous-conductive-parts with that system. Again, can't rely on that for protection against electric shock … but this time we definitely need to size our cpc's in a similar manner to TN systems for protection against overcurrent (earth fault current). Again, the RCD is not an overcurrent protective device according to BS 7671, it requires back-up of a suitable overcurrent protective device, and the cpc sized accordingly.”

    But if the stable has no extraneous-conductive-parts and is of wooden construction, perhaps with a blue plastic water pipe only, that puts a different complexion on things.

    Z.
     

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