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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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    no, the gas tubes fail open, and if grossly overloaded the seals fail, gas escapes and air gets in raising the breakdown voltage higher. Hence the use of a GDT for the NE connection.

    I'd believe GDTs are unlikely to fail to short (certainly a lot less likely than the MOVs) - but if it's really impossible, why all the fuss banning them from L-PE connections on TT systems (CT2 etc)? (From what I can see the performance characteristics can be made pretty similar to MOV ones).

    … and how would that out-of-service flagging mechanism work - if the GDT fails would there reliably be enough energy in the surge to melt that solder blob?

        - Andy.

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  • 0

    no, the gas tubes fail open, and if grossly overloaded the seals fail, gas escapes and air gets in raising the breakdown voltage higher. Hence the use of a GDT for the NE connection.

    I'd believe GDTs are unlikely to fail to short (certainly a lot less likely than the MOVs) - but if it's really impossible, why all the fuss banning them from L-PE connections on TT systems (CT2 etc)? (From what I can see the performance characteristics can be made pretty similar to MOV ones).

    … and how would that out-of-service flagging mechanism work - if the GDT fails would there reliably be enough energy in the surge to melt that solder blob?

        - Andy.

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