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EICR - main earth and neutral

Former Community Member
Former Community Member
Hi was conducting a EICR on a consumer unit today removed the cover and Main earth cable was 8 x single strand insulated cables istead of expected single 25mm also earth was the same??? it is in an apartment and has been running fine for

at least 20 years, just want to know what to input for csa?? and should I note it in observations under C3 CODE???? ANY ADVISE WELCOME THANKS
  • 0
    Not quite sure what you are describing.
  • 0
    Sounds like a split concentric cable which if this is the case then perfectly acceptable.
  • 0
    Have you took the cover off the DNO fuse holder rather than the consumer unit?


    Where is the suppliers meter?
  • 0
    To be frank and honest here i’m afraid  , any electrician or electricial inspector who doesn’t know what you are clearly describing should at best ask themselves - am i confident , knowledgeable , qualified and above all safe in what i’m doing .

    Carrying out an eicr without knowing what a split concentric cable is , leaves nothing but concerns .
  • 0
    If it looks a bit like this stuff. then as others have said,
    59d15a4653d6b028bdef62fe6ee9b319-original-splitcon.jpg


     It is split concentric cable - common for use by DNOs, not quite as good as SWA as there is not an overall earthed armour - half of the 'not really an armour' is neutral. but easy to work with and good for EMC. Can be buried, but needs to meet the same routing rules in walls like T and E to meet BS7671.

    CSA is normally stamped on the jacket, but if not, size from the live core, N has slightly more current handling capacity, being better cooled

    Mike
  • 0
    Also -
    raddish46:

    Hi was conducting a EICR on a consumer unit today removed the cover and Main earth cable was 8 x single strand insulated cables istead of expected single 25mm also earth was the same???



    I suppose we know what you meant, but...


  • 0
    Another example. Now discuss if this is permitted because I won't.
  • 0
    istead of expected single 25mm

    As it's an apartment, I wouldn't be at all surprised if it was fused down after the cut-out - and thus a smaller size could be expected (often 16mm² perhaps even 10mm² if the load was expected to be modest).


    Split-con often used to be used in place of SWA (as it's much easier to handle and terminate), but has a few disadvantages for modern requirements - firstly much of the "armour" is N rather than PE, so it's not suitable for avoiding 30mA RCD protection when concealed in a wall or similar - so basically treat it as if it were T&E rather than SWA. Also some care is needed with fault protection - since the plastic covering on the individual strands of the N mean that fault currents aren't necessarily shared between all of the strands if the fault occurs before the final terminal, unlike a normal stranded conductor, so you might want to think about  fault protection of conductors in parallel (e.g. appendix 10 of BS 7671).


       - Andy.
  • 0
    davezawadi (David Stone):

    Another example. Now discuss if this is permitted because I won't.




    You have already discussed it and the answer isn’t clear cut.

    https://communities.theiet.org/discussions/viewtopic/1037/25616


    I asked where the meter is with the intention of trying to determine if the cable should be classified as suppliers equipment or part of the consumers installation, the next question is what fuses are installed to protect this cable, is protected by the suppliers fuse or a fuse within the consumers installation?


  • 0
    Andy raises an interesting point - what do you need to consider for fault protection (adiabatic) in this case?


    It's entirely possible (and perhaps more likely) that a line to neutral or line to earth fault will only short line to a single strand of the neutral or earth (or perhaps a few strands).


    In a 25 mm2 split-concentric cable, the equivalent CSA of each neutral strand (11 x 1.7 mm) is 2.27 mm2, and that of each cpc strand (4 x 2.25 mm) is 4.0 mm2.


    Immediately you can see the neutral fault is the worst-case. So if you're using BS 88-3 fuses,


    The next step depends on which of the following scenarios you follow:
    1. The neutral strand is broken so fault current flows only one way.

    • The neutral strand is not broken, so roughly half the fault current flows in each direction and in the case of the downstream current returns down the other neutral strands.


    Supposing either is possible, then 1. is the worst-case from an adiabatic perspective.


    Using BS 88-3 fuses to protect the cable, the lengths of the cables are limited by the minimum prospective fault current:
    • for 63 A BS 88-3 fuse, the minimum prospective fault current is approx 900 A and max length of run is 2.8 m with 1 kA pfc at building network origin, or 24 m with 5 kA pfc at building network origin

    • for 45 A BS 88-3 fuse, the minimum prospective fault current is approx 430 A and max length of run is 34 m with 1 kA pfc at building network origin, or 55 m with 5 kA pfc at building network origin

    • for 32 A BS 88-3 fuse, the minimum prospective fault current is approx 160 A and max length of run is 135 m with 1 kA pfc at building network origin, or 156 m with 5 kA pfc at building network origin

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