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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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  • 0

    mapj1: 
     

    Can these things really go permanently short circuit?

    Yes, or at least with the sort of fault currents you will see in a TT system they are not always enough to blow clear. I suspect in TNS, TNC-s there is enough PSSC to vaporise something smartly, so they will eventually fail to an open state .

    The same things have been found inside well designed electronics for years, and they do fail more or less dead short in the face of any event that takes the spot dissipation inside higher than it can handle.

    Mike.

    Even gas discharge tubes as found in the Wylex neutral S.P.Ds?

    Z.

Reply
  • 0

    mapj1: 
     

    Can these things really go permanently short circuit?

    Yes, or at least with the sort of fault currents you will see in a TT system they are not always enough to blow clear. I suspect in TNS, TNC-s there is enough PSSC to vaporise something smartly, so they will eventually fail to an open state .

    The same things have been found inside well designed electronics for years, and they do fail more or less dead short in the face of any event that takes the spot dissipation inside higher than it can handle.

    Mike.

    Even gas discharge tubes as found in the Wylex neutral S.P.Ds?

    Z.

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