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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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    mapj1:.


    BUT it sounds like no RCD at the origin, so be aware it is not ideal, you need some sort of RCD covering the socket and in the current regs to rely on an RCD socket to do this is strictly a non-compliance.


    Mike




    This needs expanding, the issues of having RCD sockets rather than RCD protection at the consumer unit:



    • You are relying purely on an over current device to disconnect an earth fault, so the earth loop impedance must be lower than if the circuit was 30 mA RCD protected.

    • There may be an issue with cables concealed in walls.

    • There may be an issue with cables within metal stud walls.

    • As Mike says RCD sockets are strictly a non-compliance and the proposal is to add another one to the existing circuit rather than upgrading the circuit protection by adding a 30 mA RCD.

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  • 0
    mapj1:.


    BUT it sounds like no RCD at the origin, so be aware it is not ideal, you need some sort of RCD covering the socket and in the current regs to rely on an RCD socket to do this is strictly a non-compliance.


    Mike




    This needs expanding, the issues of having RCD sockets rather than RCD protection at the consumer unit:



    • You are relying purely on an over current device to disconnect an earth fault, so the earth loop impedance must be lower than if the circuit was 30 mA RCD protected.

    • There may be an issue with cables concealed in walls.

    • There may be an issue with cables within metal stud walls.

    • As Mike says RCD sockets are strictly a non-compliance and the proposal is to add another one to the existing circuit rather than upgrading the circuit protection by adding a 30 mA RCD.

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