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Unfused spur.

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Hello All,


Could an unfused R.C.D. protected spur, from a complient ring final circuit, supplying a single outdoor socket via 1.5mm2 6242Y cable of max. length 300mm through a brick wall from an indoor socket outlet be considered compliant?


Z.
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  • 0
    It is satisfactory Andy, 1 mm2 and 1kA is safe for 13 milliseconds to 70 degrees. A B32 will easily break that.

    Not according to BS EN 60898 (or BS EN 61009) as far as I can tell. It seems a 6kA rated B32 can have an energy let-through of anything up to 45,000 A²s - even a 3kA device is permitted up to 18,000 - whereas a 1mm² conductor in a PVC cable (final temperature 160 degrees, k=115) can only withstand 13,225 A²s. As I say, by the book, some devices may well be faster in practice of course, and cables won't always be at their maximum operating temperature when the fault occurs, but it's hard for the likes of us to reliably determine that.  There must have been a a good reason we stopped using 1mm² c.p.c.s in 2.5mm² T&E after all - most manufacturers don't back changes that'll increase costs for no benefit.

     
    Hi Andy, what range do you mean by moderate to high, thanks :)

    I'd say above around 575A - on the basis that above that the 40ms a 30mA RCD should open within at that current may let through (I²t) more than the 13,225 A²s the 1mm² can officially withstand.


      - Andy.
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  • 0
    It is satisfactory Andy, 1 mm2 and 1kA is safe for 13 milliseconds to 70 degrees. A B32 will easily break that.

    Not according to BS EN 60898 (or BS EN 61009) as far as I can tell. It seems a 6kA rated B32 can have an energy let-through of anything up to 45,000 A²s - even a 3kA device is permitted up to 18,000 - whereas a 1mm² conductor in a PVC cable (final temperature 160 degrees, k=115) can only withstand 13,225 A²s. As I say, by the book, some devices may well be faster in practice of course, and cables won't always be at their maximum operating temperature when the fault occurs, but it's hard for the likes of us to reliably determine that.  There must have been a a good reason we stopped using 1mm² c.p.c.s in 2.5mm² T&E after all - most manufacturers don't back changes that'll increase costs for no benefit.

     
    Hi Andy, what range do you mean by moderate to high, thanks :)

    I'd say above around 575A - on the basis that above that the 40ms a 30mA RCD should open within at that current may let through (I²t) more than the 13,225 A²s the 1mm² can officially withstand.


      - Andy.
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