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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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    this ought to be in the test your SPD thread but 

    you can not  must not  put a GDT between L and N, as once it has struck it will not go out, rather it will sue the energy of the mains to transition from spark to glow discharge to full blown arc with impact ionisation and melting of the electrodes over a millisecond or so, and then fail spectacularly - unlike the MOV type which has a limiting action conducting at high voltage , and then as the volts fall away, the current drops back to 9/10 of very little, at least unless it was damaged. 

    Its the same reason you do not short the ballast on a florry tube.

    Mike

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  • 0

    this ought to be in the test your SPD thread but 

    you can not  must not  put a GDT between L and N, as once it has struck it will not go out, rather it will sue the energy of the mains to transition from spark to glow discharge to full blown arc with impact ionisation and melting of the electrodes over a millisecond or so, and then fail spectacularly - unlike the MOV type which has a limiting action conducting at high voltage , and then as the volts fall away, the current drops back to 9/10 of very little, at least unless it was damaged. 

    Its the same reason you do not short the ballast on a florry tube.

    Mike

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