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Cable calculations

MrJack96
Hi guys i wanted to calculate the maximum run when spuring of a ring final circuit is there any equations or is it just as simple as calculating VD to the furthest point in the ring and then VD to the end of the spur. The reason for the question is I want to spur of an existing socket using a 10meter run of 2.5 for an outside socket. Just want to Double check it’s sufficient 


thanks guys
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    Ah yes - there are two parts. one is about significantly unbalancing the ring with a point load if you have a lot of spurs from say 20% of the way round the ring.

    The other is that you have funb doing an  R1+R2 test  which is a ring round with cross-overs way to measure  (r1+r2 )/4 does not  really work well for circuits with spurs (or varying cable sizes or circuits feeding applances that provide equipotential bonding to plumbing either.).  In effect you have more than one far point on the ring, much as you can with a radial

    This does not mean you cannot wire something that way - of course you can have a short ring and a long spur, but you have to measure the r1 r2 in -situ or do some rather tedious sums properly.

    In many way on an existing system a measurement is better, as it also shows that the rest of the supply is indeed capable, and the ring really is a ring and so on.

    M.
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  • 0
    Ah yes - there are two parts. one is about significantly unbalancing the ring with a point load if you have a lot of spurs from say 20% of the way round the ring.

    The other is that you have funb doing an  R1+R2 test  which is a ring round with cross-overs way to measure  (r1+r2 )/4 does not  really work well for circuits with spurs (or varying cable sizes or circuits feeding applances that provide equipotential bonding to plumbing either.).  In effect you have more than one far point on the ring, much as you can with a radial

    This does not mean you cannot wire something that way - of course you can have a short ring and a long spur, but you have to measure the r1 r2 in -situ or do some rather tedious sums properly.

    In many way on an existing system a measurement is better, as it also shows that the rest of the supply is indeed capable, and the ring really is a ring and so on.

    M.
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